From 59ecd86b4b9b57a217f6a15a5cf501b90d205118 Mon Sep 17 00:00:00 2001
From: bashrusakh <127580858+bashrusakh@users.noreply.github.com>
Date: Thu, 18 Jun 2026 08:43:16 +1100
Subject: [PATCH] perf: isolate chat streaming renders and reduce sidebar
 render cost (#1672)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

  Reworks the chat and session-sidebar render paths to cut render cascades, memory
  churn, and UI jank on large sessions and big session trees. Behavior is preserved;
  the changes are about *when* and *how much* the UI re-renders.

  ## Chat streaming
  - Freeze the streaming message's parts in the bulk turn projection during streaming,
    and re-inject live parts only in an isolated tail leaf, so a ~60/sec delta stream
    no longer re-runs the whole-session projection or re-renders unrelated rows.
    session with referential reuse of unchanged turns.
  - Memoize message rows with field-aware comparators instead of reference equality.
  - Replace the manual child-session polling in the task tool with the live SSE
    stream + a one-shot load, removing a fetch/settle state machine.

  ## History loading & scroll
  - Load an initial page fast, then prepend one older page in the background so the
    scroll container has headroom and "load older on scroll-up" fires before the user
    hits the absolute top.
  - Compensate scroll synchronously (in a layout effect, before paint) for prepends —
    including background prepends that don't originate from a user scroll — so the
    viewport stays stable instead of judder-correcting on the next frame.

  ## Markdown rendering
  - Render markdown synchronously *styled* on first paint (paragraphs, lists, code
    cards, tables, inline code) instead of raw escaped text; the async pass then only
    upgrades syntax-highlight colors. Eliminates the flash of full-width raw text.
  - Load KaTeX CSS eagerly with the main bundle instead of inside the lazy markdown
    chunk, avoiding a late stylesheet injection on first render.

  ## Sidebar
  - Hoist per-row recursive tree walks out of row comparators into per-group
    precomputed sets/keys; batch live-session lookups into a single map; add a
    group-level memo boundary.
  - Isolate rename drafts so per-keystroke typing doesn't repaint the row tree.

  ## Sync layer
  - Add a staleness guard so a slow message fetch can't repopulate a session the user
    navigated away from.
  - Throw on fetch failure for authoritative loaders so a transient blip can't read as
    an empty server response.

  ## Cleanup
  - Remove dead code (unused hooks, params, duplicated inline types) surfaced while
    reworking the above.

  ## Known issue
  - A rare, purely cosmetic first-paint width flash can still appear on large sessions;
    it has no behavioral or data impact and is tracked for a follow-up runtime trace.
---
 CHAT_PERF_PLAN.md                             | 540 ----------------
 RIGHT_SIDEBAR_PERF_PLAN.md                    |  53 --
 .../ui/src/components/chat/ChatContainer.tsx  |  84 +--
 packages/ui/src/components/chat/ChatInput.tsx |  36 +-
 .../components/chat/MarkdownRendererImpl.tsx  |  13 +-
 .../ui/src/components/chat/MessageList.tsx    | 121 +---
 .../chat/hooks/useChatTimelineController.ts   |  69 +-
 .../components/chat/hooks/useTurnRecords.ts   |  24 +-
 .../chat/lib/messageDisplayNormalization.ts   |  79 +++
 .../chat/lib/turns/projectTurnRecords.test.ts |  21 +
 .../chat/lib/turns/projectTurnRecords.ts      |  69 +-
 .../chat/lib/turns/streamingTailEntry.test.ts | 134 ++++
 .../chat/lib/turns/streamingTailEntry.ts      |  86 +++
 .../lib/turns/turnProjectionCache.test.ts     |  35 +
 .../chat/lib/turns/turnProjectionCache.ts     |  86 +++
 .../src/components/chat/markdown/decorate.ts  |   6 +-
 .../components/chat/markdown/markdownCore.ts  |  26 +-
 .../chat/message/parts/ToolPart.tsx           | 596 +++++-------------
 .../resolveFallbackTaskSessionId.test.js      |   9 +-
 .../parts/resolveFallbackTaskSessionId.ts     |  42 +-
 .../chat/revertedMessageDockState.test.ts     |  89 +++
 .../chat/revertedMessageDockState.ts          |  73 +++
 .../components/session/SessionFolderItem.tsx  |  14 +-
 .../src/components/session/SessionSidebar.tsx | 391 +++++-------
 .../session/sidebar/SessionGroupSection.tsx   | 455 +++++++++++--
 .../session/sidebar/SessionNodeItem.tsx       | 452 ++++++++-----
 .../sidebar/SidebarActivitySections.tsx       |  70 +-
 .../session/sidebar/SidebarProjectsList.tsx   |  53 +-
 .../sidebar/hooks/useProjectRepoStatus.ts     |  39 +-
 .../sidebar/hooks/useProjectSessionLists.ts   |  45 +-
 .../hooks/useProjectSessionSelection.ts       |  23 +-
 .../sidebar/hooks/useSessionActions.ts        |   4 +-
 .../sidebar/hooks/useSidebarBulkActions.ts    | 237 +++++++
 .../session/sidebar/sessionNodeItemUtils.ts   | 120 ++++
 .../ui/src/components/ui/ScrollShadow.tsx     |   3 +-
 packages/ui/src/index.css                     |   6 +
 .../ui/src/stores/useGlobalSessionsStore.ts   |  32 +
 packages/ui/src/styles/typography.css         |  15 +
 .../src/sync/scoped-blocking-requests.test.ts |  54 ++
 .../ui/src/sync/scoped-blocking-requests.ts   |  61 ++
 packages/ui/src/sync/session-actions.ts       |  75 ++-
 .../src/sync/session-message-records.test.ts  |  68 ++
 packages/ui/src/sync/session-ui-store.ts      |   8 +
 packages/ui/src/sync/sync-context.tsx         | 223 +++++--
 packages/ui/src/sync/use-sync.ts              |  62 +-
 .../ui/src/sync/user-message-history.test.ts  |  98 +++
 packages/ui/src/sync/user-message-history.ts  |  98 +++
 47 files changed, 3168 insertions(+), 1829 deletions(-)
 delete mode 100644 CHAT_PERF_PLAN.md
 delete mode 100644 RIGHT_SIDEBAR_PERF_PLAN.md
 create mode 100644 packages/ui/src/components/chat/lib/messageDisplayNormalization.ts
 create mode 100644 packages/ui/src/components/chat/lib/turns/streamingTailEntry.test.ts
 create mode 100644 packages/ui/src/components/chat/lib/turns/streamingTailEntry.ts
 create mode 100644 packages/ui/src/components/chat/lib/turns/turnProjectionCache.test.ts
 create mode 100644 packages/ui/src/components/chat/lib/turns/turnProjectionCache.ts
 create mode 100644 packages/ui/src/components/chat/revertedMessageDockState.test.ts
 create mode 100644 packages/ui/src/components/chat/revertedMessageDockState.ts
 create mode 100644 packages/ui/src/components/session/sidebar/hooks/useSidebarBulkActions.ts
 create mode 100644 packages/ui/src/components/session/sidebar/sessionNodeItemUtils.ts
 create mode 100644 packages/ui/src/sync/scoped-blocking-requests.test.ts
 create mode 100644 packages/ui/src/sync/scoped-blocking-requests.ts
 create mode 100644 packages/ui/src/sync/session-message-records.test.ts
 create mode 100644 packages/ui/src/sync/user-message-history.test.ts
 create mode 100644 packages/ui/src/sync/user-message-history.ts

diff --git a/CHAT_PERF_PLAN.md b/CHAT_PERF_PLAN.md
deleted file mode 100644
index 75e4980a..00000000
--- a/CHAT_PERF_PLAN.md
+++ /dev/null
@@ -1,540 +0,0 @@
-# Chat Session Performance Plan
-
-## Goal
-
-Reduce render cost and history-load latency when switching between chat sessions
-in `packages/ui/src/components/chat/`, especially on Windows desktop with
-projects that have a long-running chat history (50–500 messages per session,
-tool-heavy workloads where each tool call returns 10–200 KB of output).
-
-The plan is **strictly behavior-preserving**: every change keeps the visible
-behavior 1:1 with the current build. Differences are only in the cost of doing
-the work, not in the UX, layout, limits, persistence, or order of operations.
-
-The two scenarios this targets:
-
-- Switching between sessions in the sidebar (especially in/out of a session
-  with a long history) — the main window currently blocks the main thread
-  for 200–500 ms on first paint while `JSON.parse` + `materializeSessionSnapshots`
-  + `projectTurnRecords` run synchronously over the full initial page.
-- Returning to a session you visited a few minutes ago — the in-memory LRU
-  (`SESSION_MESSAGE_RECORDS_CACHE_MAX = 40` desktop) helps, but the second
-  visit to a session outside that window still pays the full network + parse
-  cost.
-
-A secondary goal is to avoid hammering the OpenCode server with large
-single-shot fetches; we want smaller, more frequent, deduped requests.
-
-## Upstream context
-
-Before implementing, I scanned open/closed PRs for overlap and lessons:
-
-- **#1651 — "perf: migrate chat rendering to virtua"** (`b920fd6f`, MERGED).
-  Already moved chat history to `virtua` virtualization with `bufferSize: 900`
-  and `MESSAGE_LIST_VIRTUALIZE_THRESHOLD = 5`, plus deferred Prism highlight,
-  mermaid/file annotation, table listeners, stable plugin lists. This plan
-  builds on top of that.
-- **#1650 — "perf: instant startup via cache hydration + decoupled readiness"**
-  (`c62f0d1c`, MERGED). Instant startup + decoupled readiness — orthogonal.
-- **#1503 — "fix(chat): do not force scroll in thinking block during streaming"**
-  (OPEN). Scroll behaviour during streaming — not in our hot path.
-- **#1584 — "feat: improve long user message collapse, scrolling, and navigation"**
-  (DRAFT). Touches long user messages; no direct conflict with this plan.
-- **#1621 — "feat: comprehensive scrolling and navigation improvements"**
-  (DRAFT). Broad scroll/navigation PR; no direct conflict.
-- **#1282 — "Optimize large-session sidebar trees, switching UX, and chat
-  scroll restore stability"** (CLOSED by maintainer). Introduced session-
-  switching instability, selection/chat desync, optimistic transitions.
-  Lesson: keep this plan focused on render-cost reduction and stable memoization;
-  do NOT add optimistic transitions, backend search endpoints, scroll-
-  restoration loops, or pagination on top of an unstable base.
-- **#1448 — "feat: implement unified multi-server sidebar"** (DRAFT). Rewrites
-  large parts of `SessionSidebar`. Independent of this plan.
-
-There is currently NO open PR targeting the same render-cost or history-load
-problems for the chat panel. We can proceed without coordination.
-
-## Current Architecture Notes
-
-### Data flow on session switch
-
-1. `ChatContainer` subscribes to `currentSessionId` from `useSessionUIStore`.
-2. `useSessionMessageRecords(currentSessionId, directory)` reads from the
-   directory-scoped sync store via `React.useSyncExternalStore`. Snapshot
-   cache: `SESSION_MESSAGE_RECORDS_CACHE_MAX = 40` desktop, `4` vscode/mobile.
-3. `useChatTimelineController.turnWindowModel` is rebuilt via
-   `buildTurnWindowModel(messages)` on first open of a session; cached per
-   sessionId in module-level `turnModelCache` (max 30 desktop, 4 constrained).
-4. `MessageList.baseDisplayMessages` reverses + dedupes + normalizes each
-   message via `getNormalizedMessageForDisplay` (per-message `WeakMap` cache).
-5. `useTurnRecords` projects turn records via `projectTurnRecords` (O(N) over
-   messages + per-turn work for summary/activity/diffStats/changedFiles).
-   `previousProjectionRef` stabilizes across re-renders, but there is no
-   module-level projection cache — returning to a session after the component
-   unmounts pays the full projection cost again.
-6. `useChatTimelineController` runs the `useLayoutEffect` on `[sessionId]`
-   that resets `isLoadingOlder`, `pendingRevealWork`, `activeTurnId`.
-
-### Render hot path (current cost map)
-
-- `ChatContainer` (990 lines) subscribes to the full directory `permission`
-  and `question` records via `useDirectorySync((s) => s.permission ?? {})` and
-  `useDirectorySync((s) => s.question ?? {})` (`ChatContainer.tsx:436-443`).
-  Any `permission.asked` or `question.asked` event for any session in the
-  same directory re-renders `ChatContainer` and re-runs the `permissionsMap` /
-  `questionsMap` / `scopedSessionIds` / `sessionPermissions` / `sessionQuestions`
-  / `sessionIsWorking` chain. Same for `useSessions(directory)` — every
-  `session.updated` event for any session in the directory re-renders the
-  container.
-- `MessageList.reviewTransferDirection` (`MessageList.tsx:1151`) does
-  `useGlobalSessionsStore((state) => { const currentSession = state.activeSessions.find(...) })`
-  — runs `find` + `some` over the entire global active list on every global
-  store change.
-- `MessageList` already has a `useStableEvent(getAnimationHandlers)`,
-  `useStableEvent(scrollToBottom)`, and a module-level `timelineCache` for
-  the virtua cache snapshot — those are the right pattern, just not applied
-  uniformly.
-- `ChatMessage` (1182 lines) is `React.memo`-wrapped with
-  `areRenderRelevantMessagesEqual` plus `areRelevantTurnGroupingContextsEqual`.
-  `MessageBody` (2121 lines) is NOT `React.memo`-wrapped but is only
-  rendered through `MessageRow` → `ChatMessage` and only re-runs when
-  `areRenderRelevantMessagesEqual` returns false.
-
-### The 1.5 MB problem
-
-The OpenCode server (separate repo, `anomalyco/opencode`) responds to
-`GET /api/session/{sessionID}/message` with
-`Array<{ info: Message, parts: Part[] }>` (the v1 wire shape preserved in
-the v2 SDK). On a typical tool-heavy session of 150 messages, this array
-serializes to ~1.5 MB of JSON. The bulk is `ToolStateCompleted.output: string`
-(confirmed in `node_modules/.bun/@opencode-ai+sdk@1.17.7/.../types.gen.d.ts:357-373`).
-
-The OpenChamber web server (`packages/web/server/index.js:1115`) installs
-Express `compression()` middleware BEFORE the OpenCode proxy
-(`packages/web/server/lib/opencode/proxy.js`), so the response IS compressed
-on the way out (5x reduction on typical JSON, so ~300 KB on the wire). The
-proxy explicitly sets `accept-encoding: identity` (`proxy.js:629`) which is
-a no-op against the upstream OpenCode server (it has no compression
-middleware — `server.ts` uses raw `@effect/platform-node` NodeHttpServer).
-
-So the **wire cost is ~300 KB after gzip**, not 1.5 MB. The real cost is the
-**client-side main-thread blocking**:
-
-- `JSON.parse` on 1.5 MB of structured data: ~50–200 ms in V8.
-- `materializeSessionSnapshots`: O(N) sort/filter, ~10–20 ms for 150.
-- `projectTurnRecords`: O(N) with per-turn work (summary/activity/diffStats/
-  changedFiles/indexes), ~30–100 ms for 150.
-- `useChatTimelineController.useLayoutEffect` re-resolves pending scroll
-  requests and updates `historySignals` — fast but runs synchronously.
-
-Total main-thread block on first paint: **200–500 ms**. The user-perceived
-"long load" is mostly this.
-
-### Limit constants (current)
-
-| Constant                              | Value                             | Location              | Purpose                                 |
-| ------------------------------------- | --------------------------------- | --------------------- | --------------------------------------- |
-| `INITIAL_MESSAGE_PAGE_SIZE`             | 150 (desktop), 30 (vscode/mobile) | `use-sync.ts:25-27`     | First page on session switch            |
-| `HISTORY_MESSAGE_PAGE_SIZE`             | 200                               | `use-sync.ts:28`        | Scroll-up pagination                    |
-| `MESSAGE_REFETCH_LIMIT`                 | 200                               | `session-actions.ts:27` | Refetch after revert/abort              |
-| `RECONNECT_MESSAGE_LIMIT`               | 30                                | `sync-context.tsx:193`  | Reconnect bootstrap                     |
-| `SESSION_MATERIALIZATION_MESSAGE_LIMIT` | 30                                | `sync-context.tsx:194`  | Materialize on `message.updated` recovery |
-| `DEFAULT_MESSAGE_LIMIT`                 | 200                               | `sessionTypes.ts:78`    | Declarative ceiling; not enforced       |
-
-For 99% of sessions, users read the latest 30–50 messages and rarely scroll
-beyond. The 150-initial / 200-history combination fetches ~3x more than the
-visible window on first paint.
-
-### Already optimized (do not touch)
-
-- `MessageList` virtualization with `virtua` at threshold 5, bufferSize 900
-  (PR #1651).
-- `MessageRow` / `ChatMessage` / `TurnBlock` `React.memo` with custom
-  comparators.
-- `getNormalizedMessageForDisplay` per-message `WeakMap` cache.
-- `MarkdownRenderer` lazy-loaded via `lazyWithChunkRecovery`; Prism highlight
-  and mermaid deferred (PR #1651).
-- `expandedToolsStateCache` and `collapsedToolsStateCache` module-level LRU
-  bounded at 4000 (`ChatMessage.tsx:39-95`).
-- `aggregateLiveSessions` / `aggregateLiveSessionStatuses` bail via
-  `areSessionListsEquivalent` and `areStatusMapsEquivalent`; consumed through
-  `useLiveSyncSelector`.
-- `useStickyProjectHeaders` IntersectionObserver.
-- Targeted field cloning in `handleDirectoryEvent` (sync/DOCUMENTATION.md).
-- `turnModelCache` for `buildTurnWindowModel` (30 desktop, 4 vscode/mobile).
-- `timelineCache` for virtua snapshot (max 16 sessions).
-- `session-prefetch-cache` 15s TTL dedup of `syncSession` requests.
-- `syncSessionInflightByKey` for in-flight dedup.
-
-## Proposed Architecture
-
-### Bugfix Layer 0 — Fix rapid project-switch race in sidebar
-
-**Observed bug:** When connected from desktop to an OpenChamber server, with
-multiple trees in the sidebar and large sessions (~200k context), rapidly
-switching between recent sessions in different projects causes the focus to
-follow the **fetch completion order** instead of the user's final click. The
-sequence is: user clicks 1, then 2, then 3; UI briefly shows 3; when fetch 1
-finishes it jumps to 1; when fetch 2 finishes it jumps to 2; when fetch 3
-finishes it finally lands on 3.
-
-**Root cause:** `useProjectSessionSelection` (`useProjectSessionSelection.ts`)
-has auto-selection logic that runs when `activeProjectId` changes. Combined
-with uncancelled async fetches and cross-project store updates, stale fetch
-completions update the sidebar session lists, which re-triggers selection
-fallbacks and overwrites the user's explicit choice.
-
-**Fix — four parts:**
-
-1. **Layer 0a — Generation guard in `useEnsureSessionMessages`.**
-   Track a per-hook generation counter. When the effect fires for a new
-   `sessionID`, increment the generation. Ignore the result (do not apply
-   store mutations) if the generation is stale by the time the async fetch
-   completes.
-
-2. **Layer 0b — Generation guard in `syncSession` / `loadMessages`.**
-   Add a module-level `Map<sessionKey, number>` tracking the latest requested
-   generation per session. Before every store write inside `syncSession` and
-   `loadMessages`, check that the request is still current. This prevents
-   fetches 1 and 2 from mutating state after the user has already selected 3.
-
-3. **Layer 0c — Debounce `handleSessionSelect`.**
-   In `useSessionActions.ts`, wrap the actual navigation in a short timeout
-   (~80ms). The first click executes immediately; rapid subsequent clicks
-   cancel the pending navigation and reschedule for the latest target. This
-   coalesces 1→2→3 into a single `setCurrentSession(3)` call.
-
-4. **Layer 0d — Explicit-selection guard in `useProjectSessionSelection`.**
-   Track the timestamp of the last explicit user selection. Suppress the
-   auto-select fallback in the layout effect for ~500ms after an explicit
-   click, so fallback logic never overwrites an active user choice.
-
-**Effect:** Rapid project switching becomes deterministic: the UI stays on the
-last clicked session and only loads its content. Stale fetches are silently
-ignored instead of fighting for focus.
-
-**Files:** `sync-context.tsx`, `use-sync.ts`, `useSessionActions.ts`,
-`useProjectSessionSelection.ts`.
-
----
-
-### Layer 1 — Narrow subscriptions in ChatContainer
-
-**Problem:** `ChatContainer.tsx:436-443` subscribes to the **full directory**
-`permission` and `question` records. Any permission/question event for **any**
-session in the directory causes a ChatContainer re-render, even if the event
-is for an unrelated session. Same for `useSessions(directory)` at line 427
-— every `session.updated` event re-renders the container.
-
-There are already session-scoped hooks (`useSessionPermissions(sessionID)`,
-`useSessionQuestions(sessionID)` at `sync-context.tsx:2151,2165`), but they
-don't aggregate across descendant subagent sessions — which
-`collectVisibleSessionIdsForBlockingRequests` (`ChatContainer.tsx:458-464`)
-handles for the `sessionPermissions` / `sessionQuestions` / `sessionIsWorking`
-chain.
-
-**Fix:** Replace the broad directory reads with scoped subtree selectors. The
-subtree is the current session and all its descendant subagent sessions.
-
-Add to `sync-context.tsx`:
-
-- `useScopedSubtreeIds(sessionID: string | null, directory?: string): Set<string>`
-  — returns the set of session IDs in the current subtree (current session +
-  all descendants by `parentID`). Reference-stabilized: a new Set is only
-  returned when the actual membership changes, using the same "compare
-  contents, reuse reference" pattern as `areSessionListsEquivalent`.
-
-- `useScopedBlockingRequests(sessionID: string | null, directory: string, kind: 'permission' | 'question')`
-  — combines `useScopedSubtreeIds` with the existing `useSessionPermissions` /
-  `useSessionQuestions` patterns to return a flat array of blocking requests
-  scoped to the subtree only.
-
-- `useParentSession(sessionID: string | null): Session | null` — returns
-  the parent Session via a pre-computed `Map<sessionId, Session>` that only
-  changes when the target session or its parent changes. Replaces the O(N)
-  `.find()` at `ChatContainer.tsx:564`.
-
-`ChatContainer` then:
-- reads `useScopedBlockingRequests` instead of the full `allPermissions`/
-  `allQuestions` → `permissionsMap` → `scopedSessionIds` → `sessionPermissions`
-  / `sessionQuestions` chain.
-- reads `useParentSession` instead of `sessions.find(...)`.
-- stops subscribing to `useSessions(directory)` entirely (the subtree selectors
-  provide all needed session data scoped to the active subtree).
-
-**Effect:** Third-party sessions in the same directory stop re-rendering
-ChatContainer. Streaming events for unrelated sessions no longer invalidate
-the chat's blocking-requests chain.
-
-**Files:** `ChatContainer.tsx`, `sync-context.tsx`.
-
----
-
-### Layer 3 — Module-level projection cache
-
-**Problem:** `useTurnRecords` keeps `previousProjectionRef` for in-component
-stabilization, but a session that unmounts and remounts loses that ref. Full
-re-projection cost is paid every time you return to a session.
-
-**Fix:** Add a module-level LRU keyed by `sessionKey`. The cache key must
-capture the exact identity of the message list to avoid stale projections:
-
-```ts
-// Includes: sessionKey, message count, last message id,
-// AND the count of parts on the last message (detects streaming deltas
-// that add parts to an existing message without changing id or count).
-type CacheKey = `${sessionKey}|${length}|${lastMessageId ?? ''}|${lastMessagePartCount ?? 0}`
-const projectionCache = new Map<CacheKey, { projection: TurnProjectionResult }>()
-```
-
-Including `lastMessagePartCount` is critical: during streaming, new parts are
-appended to the same last message — the message ID and total message count
-stay the same, but the projection must be recomputed.
-
-Cap at the same limits as `turnModelCache` (30 desktop, 4 vscode/mobile)
-to bound memory.
-
-`useTurnRecords` consults the cache before running `projectTurnRecords`; on
-hit, returns the cached projection and refreshes LRU order; on miss, runs the
-full projection and writes the result.
-
-**Effect:** Returning to a session within the LRU window is zero projection
-work. Combined with `MessageList.timelineCache` (which already caches the
-virtua snapshot), the first paint after a remount is essentially "rebuild
-only what's strictly session-specific (resolvers, refs)".
-
-**Files:** `useTurnRecords.ts` (small extension) + new helper
-`lib/turns/turnProjectionCache.ts`.
-
----
-
-### Layer 4a — Start message fetch synchronously in setCurrentSession
-
-**Problem:** `session-ui-store.setCurrentSession` currently only calls
-`setState` (Zustand). The actual message fetch is started by
-`ChatContainer.useEffect` at `ChatContainer.tsx:787-792`, which runs on the
-render AFTER the state update — adding one React commit cycle (~30–80 ms)
-of latency before the network request starts.
-
-**Fix:** Start the fetch directly from `setCurrentSession` on the same tick
-as the state update, using the existing imperative access layer.
-
-The approach uses `session-actions.ts`, which already has module-level refs
-(`_sdk`, `_childStores`, `_getDirectory` — `session-actions.ts:33-35`) set by
-SyncProvider at mount time. Add a `fetchMessagesForSession(sessionID: string)`
-function there that duplicates the core path from `useSync().syncSession`:
-checks the child store for existing messages, fetches from SDK if needed,
-calls `materializeSessionSnapshots`, and writes to the directory store.
-
-`setCurrentSession` then calls `fetchMessagesForSession(targetId)` immediately
-after `set({ currentSessionId: id, ... })`. The `syncSessionInflightByKey`
-in `use-sync.ts` doesn't cover this new path, so the function also uses the
-existing `_ensureMessagesLoading` Set in `sync-context.tsx` (line 2668) for
-dedup.
-
-The existing `ChatContainer.useEffect` at line 787 stays as a safety net for
-sessions restored from URL or other non-sidebar entry points.
-
-**Effect:** Fetch starts on the same tick as the state update, ~30–80 ms
-earlier than the current "wait for React commit → useEffect → fetch" path.
-
-**Files:** `session-ui-store.ts` (one new call in `setCurrentSession`),
-`session-actions.ts` (new `fetchMessagesForSession` function).
-
----
-
-### Layer 5 — Small wins
-
-- **`reviewTransferDirection` pre-computed map.** In
-  `MessageList.tsx:1151-1164`, replace
-  `useGlobalSessionsStore((state) => state.activeSessions.find(...))` with
-  a selector that reads a pre-computed `Map<sessionId, ReviewTransferDirection>`
-  maintained by `useGlobalSessionsStore` (built once per active-sessions
-  change, in the same reducer that updates `activeSessions`). Same selector
-  shape from the component's perspective, but no `.find()` + `.some()` on
-  every global store change.
-
-- **`parentSession` lookup.** Part of Layer 1 (see `useParentSession` hook
-  above). The pre-computed `Map<sessionId, Session>` is maintained in
-  `sync-context.tsx` and read via the hook, eliminating the O(N) `.find()`
-  in `ChatContainer`.
-
-**Files:** `MessageList.tsx`, `useGlobalSessionsStore.ts`.
-
----
-
-### Layer 6a — Reduce initial payload
-
-Lower the page sizes to match typical user reading patterns:
-
-- `INITIAL_MESSAGE_PAGE_SIZE`: 150 → 50 (desktop), 30 stays (vscode/mobile).
-- `HISTORY_MESSAGE_PAGE_SIZE`: 200 → 100.
-- `MESSAGE_REFETCH_LIMIT`: 200 → 100.
-- `DEFAULT_MESSAGE_LIMIT` in `sessionTypes.ts`: stays 200 (it's a ceiling,
-  not a fetch target).
-
-**How the "load more" indicator still works with a smaller initial page:**
-`historyMeta` in ChatContainer is built from `sync.hasMore(currentSessionId)`,
-which reads `meta.current` (set immediately after the first `loadMessages`
-call, before the component renders). If the server returns a cursor,
-`sync.hasMore()` returns `true` → `historyMeta.complete = false` →
-`hasMoreAboveTurns = true` → scroll-up indicator appears correctly.
-The `messages.length >= defaultLimit` fallback is never reached in practice
-because `historyMeta` is populated before the first render of the chat.
-
-Effect on the 1.5 MB problem:
-
-- Initial fetch payload: 1.5 MB → ~500 KB parsed (50 messages).
-- JSON.parse cost: 100–200 ms → 30–70 ms.
-- projection cost: 30–100 ms → 10–30 ms.
-- Combined main-thread block: 200–500 ms → 50–150 ms.
-
-User cost: one extra round trip when scrolling past the 50th message. The
-scroll-triggered `loadMore` is already in place and is the right UX for "I
-want to see older messages" — the previous behavior of "fetch 150 and ignore
-100" was wasted work for the common case.
-
-**Files:** `use-sync.ts`, `session-actions.ts`.
-
----
-
-### Layer 6b — Progressive mount
-
-`use-sync.syncSession` starts the initial 50-message page synchronously.
-After the first page resolves, if the cursor indicates more messages, a
-second fetch of `HISTORY_MESSAGE_PAGE_SIZE` (100 messages) is dispatched
-via `loadMessages(sessionID, { before: cursor, mode: "prepend" })` — the
-prepend mode already exists in `loadMessages` (`use-sync.ts:373`). This
-second page is non-blocking; the user sees the first 50 messages immediately.
-
-On the client side, `useTurnRecords` and `useChatTimelineController` must
-re-run projection when the prepended messages arrive. Two options:
-
-- **Simple:** Let the full re-projection run on the second page arrival
-  (50→150 messages). With Layer 6a, projection of 150 messages is ~10–30 ms —
-  fast enough that a one-time re-project on the second page is acceptable.
-
-- **Optimal:** Extend `updateTurnWindowModelIncremental` (currently handles
-  only +1 message appends — `windowTurns.ts:76-84` checks
-  `nextMessages.length !== previousMessages.length + 1`) to handle batch
-  prepends. This requires:
-  1. A new `updateTurnWindowModelBatchPrepend` that verifies the new messages
-     are all prepended (all existing message references match at the tail)
-     and projects only the new messages into turn windows.
-  2. A corresponding `updateTurnProjectionIncremental` in `projectTurnRecords.ts`
-     that merges the new turns into the existing projection.
-
-  Because `updateTurnWindowModelIncremental` is designed for single-message
-  streaming deltas (not batch prepends), this is non-trivial additional work.
-  Given Layer 6a alone reduces the main-thread block to ~50–150 ms, start
-  with the simple approach and measure before committing to the incremental
-  path.
-
-**Net effect:** The first 50 messages mount within the same time as today
-(possibly faster, because parsing 500 KB < parsing 1.5 MB). The next 100
-arrive ~200–400 ms later. From the user's perspective, the chat becomes
-interactive immediately.
-
-**Files:** `use-sync.ts`, `ChatContainer.tsx` (small — no change to `loadMore` UX).
-
----
-
-## What I do not propose to touch (and why)
-
-- `useChatAutoFollow` and the scroll-restoration logic in
-  `useChatTimelineController` (the `prePrependScrollRef` / height-delta
-  compensation). PR #1282 closed because of scroll-restore regressions;
-  these are working and tested.
-- The event-pipeline coalescing and `message.part.delta` reducer path.
-  Already correct (sync/DOCUMENTATION.md).
-- The Markdown renderer and Prism highlight deferral. PR #1651 already took
-  the low-hanging fruit.
-- The `key={currentSessionId}` on `<ChatViewport>`. Forces a full remount,
-  which is expensive, but a previous PR attempt (Layer 2 in the sidebar
-  plan) regressed scroll/follow. Keeping the remount for now.
-- The OpenCode server response shape. It's in `anomalyco/opencode`, which
-  AGENTS.md forbids us from touching.
-- The SDK's internal `JSON.parse` step. Replacing it with a streaming
-  parser requires owning the fetch call (the SDK doesn't expose the
-  `ReadableStream`), and the response is a single JSON array, not NDJSON —
-  so streaming buys us the same "first N visible, rest in background"
-  pattern that Layer 6b already implements.
-- Tool output lazy-load. Would need a server-side endpoint like
-  `GET /api/session/{sid}/part/{partID}` that the OpenCode server does
-  not currently provide.
-
-## Expected effect
-
-- **Initial session switch on a 150-message tool-heavy session:**
-  main-thread block 200–500 ms → 50–150 ms. ~3x faster.
-- **Wire payload on the same session:** 1.5 MB parsed → 500 KB parsed.
-  After gzip, ~300 KB → ~100 KB.
-- **Returning to a session within the LRU window:** zero projection work
-  (Layer 3), zero scroll-cache rebuild (existing `timelineCache`).
-- **Returning to a session outside the LRU window:** same as initial, but
-  the 15s `session-prefetch-cache` TTL catches sessions visited twice in
-  rapid succession.
-- **Server load:** the OpenCode server processes 1/3 the volume per
-  session-switch, and the warm second page in Layer 6b is deduped
-  against the inflight request. Strictly less load than today.
-
-## Files Touched by the Plan
-
-- `CHAT_PERF_PLAN.md` (new, this file)
-- `packages/ui/src/sync/sync-context.tsx` (Bugfix Layer 0a — `useEnsureSessionMessages` guard)
-- `packages/ui/src/sync/use-sync.ts` (Bugfix Layer 0b — `syncSession`/`loadMessages` guard; Layer 6a — constants)
-- `packages/ui/src/components/session/sidebar/hooks/useSessionActions.ts` (Bugfix Layer 0c — debounce)
-- `packages/ui/src/components/session/sidebar/hooks/useProjectSessionSelection.ts` (Bugfix Layer 0d — explicit-selection guard)
-- `packages/ui/src/components/chat/ChatContainer.tsx` (Layers 1, 6b)
-- `packages/ui/src/components/chat/MessageList.tsx` (Layer 5a)
-- `packages/ui/src/stores/useGlobalSessionsStore.ts` (Layer 5a — pre-computed map)
-- `packages/ui/src/sync/sync-context.tsx` (Layer 1 — new hooks: `useScopedSubtreeIds`, `useScopedBlockingRequests`, `useParentSession`)
-- `packages/ui/src/sync/session-ui-store.ts` (Layer 4a — call fetch from `setCurrentSession`)
-- `packages/ui/src/sync/session-actions.ts` (Layer 4a — new `fetchMessagesForSession`, Layer 6a — constants)
-- `packages/ui/src/sync/use-sync.ts` (Layer 6a — constants, Layer 6b — progressive fetch)
-- `packages/ui/src/stores/types/sessionTypes.ts` (Layer 6a — sync `DEFAULT_MESSAGE_LIMIT` with new constants)
-- `packages/ui/src/components/chat/hooks/useTurnRecords.ts` (Layer 3 — projection cache)
-- `packages/ui/src/components/chat/lib/turns/turnProjectionCache.ts` (new, Layer 3)
-
-## Implementation order
-
-1. **Bugfix Layer 0** (race condition fixes) — highest priority, fixes the
-   observed sidebar switching bug before any optimization work.
-2. **Layer 6a** (reduce constants) — simplest performance win, also reduces
-   the race window.
-3. **Layer 3** (projection cache) — isolated change, immediate return-visit win.
-4. **Layer 5a** (reviewTransfer map) — isolated, low risk.
-5. **Layer 1** (narrow subscriptions) — more complex but well-bounded.
-6. **Layer 4a** (early fetch) — depends on Layer 1 for dedup safety.
-7. **Layer 6b** (progressive mount) — highest complexity, implement after
-   measuring real-world gains from 6a.
-
-## Conflict risks
-
-- None of the open PRs touch the files above in a conflicting way. PR #1584
-  (draft, long user message collapse) modifies `UserTextPart.tsx`, not the
-  files we touch. PR #1621 (draft, comprehensive scrolling) modifies scroll
-  and navigation components, not the chat data flow. PR #1448 (draft,
-  unified multi-server sidebar) is for `SessionSidebar.tsx` and family, not
-  the chat panel.
-- Existing internal benchmarks for `event-pipeline` are unaffected
-  (Layers 1, 3, 4a, 5, 6 do not touch event coalescing or ordering).
-- `bun run type-check` and `bun run lint` must remain green.
-
-## Open Questions
-
-1. **Layer 2 (drop `key={currentSessionId}` from `ChatViewport`):** explicitly
-   out of scope per user. Revisit after the lower-risk layers ship.
-2. **Layer 7 (Web Worker for `JSON.parse` + materialize):** out of scope.
-   The Layer 6a/6b combo should bring main-thread block to ~50–150 ms,
-   which is acceptable. Revisit if real-user feedback still shows jank.
-3. **Layer 6b incremental projection for batch prepends:** start with the
-   simple full-reproject-on-second-page approach (50→150 projection is
-   ~10–30 ms post-Layer-6a). Only build the incremental path if benchmarks
-   show the full reproject is still noticeable.
-4. **Layer 3 cache invalidation during streaming:** the `lastMessagePartCount`
-   in the cache key catches part deltas on the last message. If the streaming
-   model appends parts to a message that is NOT the last (e.g., tool output
-   on a completed turn while a new turn is streaming), the cache would miss —
-   which is correct (projection must re-run). Confirm this edge case during
-   smoke testing.
diff --git a/RIGHT_SIDEBAR_PERF_PLAN.md b/RIGHT_SIDEBAR_PERF_PLAN.md
deleted file mode 100644
index c7a37c76..00000000
--- a/RIGHT_SIDEBAR_PERF_PLAN.md
+++ /dev/null
@@ -1,53 +0,0 @@
-# Right Sidebar Performance Plan
-
-## Status — DONE (PR #1674)
-
-### P0 — Correctness / leak fixes
-
-- [x] **RightSidebar**: drop dead `useEffect` that re-nulled refs the resize handler already nulled; collapse redundant `width`/`minWidth`/`maxWidth` triple into `width` + the existing `--oc-right-sidebar-width` variable.
-- [x] **useUIStore**: clamp `setRightSidebarWidth` to `[MIN, MAX]`; simplify `setRightSidebarOpen` (22 lines → 12).
-- [x] **RightSidebarTabs / `useRightSidebarGitSync`**: takes right tab + main tab; only polls when the right git tab is the visible consumer AND the browser is online + visible. Replaces a poll that ran for the lifetime of any open sidebar.
-- [x] **GitView**: commit-files fetch refactored to `cancelled` + `Promise.all` (was a per-hash loop that could `setState` after unmount); `getRemoteUrl` and `refreshRemotes` gated on `cancelled` / `mountedRef`; new module-scoped `mountedRef` guards `setIsSettingIdentity` from firing after unmount.
-- [x] **GitView + `useGitmojiList`**: extract gitmoji fetch/cache into a hook with module-level inflight promise + subscribers Set; stale-while-revalidate from localStorage; `ensureLoaded()` for call-site-initiated hydration; `cancelled` flag on `setIsLoading` to avoid the React setState-after-unmount race.
-- [x] **ProjectNotesTodoPanel**: 400 ms notes debounce now cancels on blur (was double-saving); `persistProjectData` chained per project through a module-level `Map<projectId, Promise>` so a fast todo toggle racing the debounced save no longer hits the server in parallel; resize auto-adjust guards against same-value pings.
-
-### P1 — Render fanout
-
-- [x] **RightSidebarTabs**: all three tab content components now always mounted with the `hidden` attribute. State and cache survive tab switches. When `activeMainTab === 'git'` (or `'context'`) the matching right tab is filtered out of the tab strip and a redirect effect snaps any persisted-but-now-hidden right tab to `'files'`. `onSelect` is now a type-guarded handler instead of `as RightTab`.
-- [x] **GitView**: 13 separate `useGitStore` action selectors collapsed into one `useShallow` block (one re-evaluation per store change instead of 13).
-- [x] **GitView**: new `isGitViewActive` flag (true when this instance is the visible consumer) gates the 7 live effects — load identities, fetch remote URL, refresh remotes, `ensureAll`, `sessionEvents.onGitRefreshHint`, worktree bootstrap poll, default-identity auto-apply. Hidden GitView instances no longer run these.
-- [x] **GitView**: `gitViewSnapshots` module-level Map is now backed by an LRU wrapper (cap 20) so per-directory draft snapshots cannot leak across hundreds of project switches. Removed the dead `unique.set` dedup in `changeEntries` — `GitStatus.files` is already unique by path.
-- [x] **SidebarFilesTree**: `statusByPath` `Map<path, FileStatus>` and `badgeByDir` `Map<dirPath, { modified, added }>` are precomputed once per `gitStatus` change. Tree render is O(1) per node instead of O(N) per node. `badgeByDir` walks each file's path segments and increments counters for every ancestor dir.
-- [x] **SidebarFilesTree**: `FileRow` wrapped in `React.memo` with a custom comparator. Context-menu open state moved INTO `FileRow` as local state — opening a menu in one row no longer re-renders siblings.
-- [x] **SidebarFilesTree**: `loadDirectory` accepts an `isCancelled` predicate; the batch-load effect for `expandedPaths` passes a stable predicate so per-dir fetches stop touching state once the effect tears down.
-- [x] **SidebarFilesTree**: module-level `fileTreeCacheByRoot` Map (LRU, cap 8 roots) hydrates `childrenByDir` / `loadErrorsByDir` / `loadedDirsRef` on mount or root change. Mirror effects write state back to the cache. Survives close-and-reopen of the right sidebar.
-
-### Review fixes (post-review)
-
-- [x] **Blocker**: `inFlightDirsRef` leak — removed `isCancelled` guard from `finally` so inflight flag always cleans up. Re-expanding a cancelled directory correctly retries.
-- [x] **Non-blocker**: duplicate `RIGHT_SIDEBAR_MAX_WIDTH` — exported from `useUIStore`, imported in `RightSidebar`. Single source of truth.
-- [x] **Non-blocker**: `useRightSidebarGitSync` poll gating — verified `shouldPoll` already includes `rightTab === 'git'`. No code change needed.
-
-## Files modified
-
-| File | Change |
-|------|--------|
-| `packages/ui/src/components/layout/RightSidebar.tsx` | Drop dead useEffect, collapse width props, import constants from store |
-| `packages/ui/src/components/layout/RightSidebarTabs.tsx` | Always-mount tabs, gated poll, redirect effect, type-guarded onSelect |
-| `packages/ui/src/components/layout/SidebarFilesTree.tsx` | Precomputed maps, React.memo(FileRow), isCancelled predicate, LRU cache |
-| `packages/ui/src/components/git/GitView.tsx` | Cancelled + Promise.all, isGitViewActive, useShallow, LRU snapshots |
-| `packages/ui/src/components/project/ProjectNotesTodoPanel.tsx` | Debounce cancel on blur, chained persistProjectData |
-| `packages/ui/src/stores/useUIStore.ts` | Clamp setRightSidebarWidth, simplify setRightSidebarOpen, export constants |
-| `packages/ui/src/hooks/useGitmojiList.ts` | **New** — module-level inflight + subscribers, localStorage cache |
-
-## Architecture notes
-
-- The redirect effect snaps `rightSidebarTab` to `'files'` whenever `activeMainTab === 'git'`, so the right and main `GitView` instances are mutually exclusive — `isGitViewActive` cannot be true for both.
-- The 7 gated effects plus the `useRightSidebarGitSync` poll cover all cases where git state should advance: visible consumer fetches; the poll keeps the store warm when only the right git tab is visible.
-- The `loadDirectory` cancellation predicate prevents stale state writes in `try`/`catch`; the `finally` block always cleans up `inFlightDirsRef`.
-
-## Out of scope (deferred)
-
-- Virtualization of `SidebarFilesTree` (large refactor; current precomputed maps already address the main bottlenecks).
-- Lazy plan titles (requires `openchamberConfig` schema changes).
-- Extracting remaining sub-views from `GitView` (large refactor, not perf-critical).
diff --git a/packages/ui/src/components/chat/ChatContainer.tsx b/packages/ui/src/components/chat/ChatContainer.tsx
index dda0700a..dcb2465f 100644
--- a/packages/ui/src/components/chat/ChatContainer.tsx
+++ b/packages/ui/src/components/chat/ChatContainer.tsx
@@ -1,5 +1,7 @@
 import React from 'react';
 import type { Message, Part, Session } from '@opencode-ai/sdk/v2';
+import type { PermissionRequest } from '@/types/permission';
+import type { QuestionRequest } from '@/types/question';
 
 import { ChatInput } from './ChatInput';
 import { DraftPresetChips } from './DraftPresetChips';
@@ -23,14 +25,8 @@ import { useDeviceInfo } from '@/lib/device';
 import { Button } from '@/components/ui/button';
 import { OverlayScrollbar } from '@/components/ui/OverlayScrollbar';
 import { Icon } from "@/components/icon/Icon";
-import type { PermissionRequest } from '@/types/permission';
-import type { QuestionRequest } from '@/types/question';
 import { cn, formatDirectoryName } from '@/lib/utils';
 import { useProjectsStore } from '@/stores/useProjectsStore';
-import {
-    collectVisibleSessionIdsForBlockingRequests,
-    flattenBlockingRequests,
-} from './lib/blockingRequests';
 
 // New sync system imports
 import { useSessionUIStore } from '@/sync/session-ui-store';
@@ -38,22 +34,21 @@ import { useStreamingStore } from '@/sync/streaming';
 import {
     useSessionMessageCount,
     useSessionMessageRecords,
-    useSessions,
-    useDirectorySync,
     useSyncDirectory,
+    useDirectorySync,
     useSessionStatus,
+    useScopedBlockingPermissions,
+    useScopedBlockingQuestions,
+    useParentSession,
 } from '@/sync/sync-context';
 import { useSync } from '@/sync/use-sync';
 import { getSessionPrefetch, subscribeSessionPrefetch } from '@/sync/session-prefetch-cache';
 import { getSessionMaterializationStatus } from '@/sync/materialization';
 import { usePlanDetection } from '@/hooks/usePlanDetection';
-import { getAllSyncSessions } from '@/sync/sync-refs';
 import { useI18n } from '@/lib/i18n';
 import { isVSCodeRuntime } from '@/lib/desktop';
 
 const EMPTY_MESSAGES: Array<{ info: Message; parts: Part[] }> = [];
-const EMPTY_PERMISSIONS: PermissionRequest[] = [];
-const EMPTY_QUESTIONS: QuestionRequest[] = [];
 const IDLE_SESSION_STATUS = { type: 'idle' as const };
 const CHAT_FORCE_SCROLL_BOTTOM_EVENT = 'openchamber:chat-force-scroll-bottom';
 const DEFAULT_RETRY_MESSAGE = 'Quota limit reached. Retrying automatically.';
@@ -140,6 +135,7 @@ type ChatViewportProps = {
     isDesktopExpandedInput: boolean;
     isMobile: boolean;
     stickyUserHeader: boolean;
+    directory?: string;
     scrollRef: React.RefObject<HTMLDivElement | null>;
     messageListRef: React.RefObject<MessageListHandle | null>;
     pendingRevealWork: boolean;
@@ -168,6 +164,7 @@ const ChatViewport = React.memo(({
     isDesktopExpandedInput,
     isMobile,
     stickyUserHeader,
+    directory,
     scrollRef,
     messageListRef,
     pendingRevealWork,
@@ -235,6 +232,7 @@ const ChatViewport = React.memo(({
                             isLoadingOlder={isLoadingOlder}
                             scrollToBottom={scrollToBottom}
                             scrollRef={scrollRef}
+                            directory={directory}
                         />
                         {(sessionQuestions.length > 0 || sessionPermissions.length > 0) && (
                             <div>
@@ -263,6 +261,7 @@ const ChatViewport = React.memo(({
         && prev.isDesktopExpandedInput === next.isDesktopExpandedInput
         && prev.isMobile === next.isMobile
         && prev.stickyUserHeader === next.stickyUserHeader
+        && prev.directory === next.directory
         && prev.scrollRef === next.scrollRef
         && prev.messageListRef === next.messageListRef
         && prev.pendingRevealWork === next.pendingRevealWork
@@ -407,7 +406,10 @@ export const ChatContainer: React.FC<ChatContainerProps> = ({ autoOpenDraft = tr
         effectiveSessionDirectory,
     );
     // Messages from sync system
-    const sessionMessageRecords = useSessionMessageRecords(currentSessionId ?? '', effectiveSessionDirectory);
+    const sessionMessageRecords = useSessionMessageRecords(currentSessionId ?? '', effectiveSessionDirectory, {
+        suspendPartUpdates: Boolean(streamingMessageId),
+        suspendPartUpdatesForMessageId: streamingMessageId,
+    });
     const sessionMessages = currentSessionId ? sessionMessageRecords : EMPTY_MESSAGES;
     const sessionPrefetchInfo = React.useSyncExternalStore(
         React.useCallback(
@@ -423,55 +425,18 @@ export const ChatContainer: React.FC<ChatContainerProps> = ({ autoOpenDraft = tr
         React.useCallback(() => undefined, []),
     );
 
-    // Sessions from sync system
-    const sessions = useSessions(effectiveSessionDirectory);
-
     // Plan detection - watches messages for plan creation and signals store
     usePlanDetection(currentSessionId ?? '', sessionMessages);
 
     // Session status from sync system
     const sessionStatusForCurrent = useSessionStatus(currentSessionId ?? '', effectiveSessionDirectory) ?? IDLE_SESSION_STATUS;
 
-    // Permissions & questions from sync system
-    const allPermissions = useDirectorySync(
-        React.useCallback((s) => s.permission ?? {}, []),
-        effectiveSessionDirectory,
-    );
-    const allQuestions = useDirectorySync(
-        React.useCallback((s) => s.question ?? {}, []),
-        effectiveSessionDirectory,
-    );
+    // Scoped blocking requests — only subscribe to permissions/questions for
+    // the current session + descendant subagent sessions, not all sessions in
+    // the directory.
+    const sessionPermissions = useScopedBlockingPermissions(currentSessionId, effectiveSessionDirectory);
+    const sessionQuestions = useScopedBlockingQuestions(currentSessionId, effectiveSessionDirectory);
 
-    // Convert Record → Map for blockingRequests helpers
-    const permissionsMap = React.useMemo(() => {
-        const m = new Map<string, PermissionRequest[]>();
-        for (const [k, v] of Object.entries(allPermissions)) m.set(k, v as PermissionRequest[]);
-        return m;
-    }, [allPermissions]);
-
-    const questionsMap = React.useMemo(() => {
-        const m = new Map<string, QuestionRequest[]>();
-        for (const [k, v] of Object.entries(allQuestions)) m.set(k, v as QuestionRequest[]);
-        return m;
-    }, [allQuestions]);
-
-    const scopedSessionIds = React.useMemo(
-        () => collectVisibleSessionIdsForBlockingRequests(
-            sessions.map((session) => ({ id: session.id, parentID: session.parentID })),
-            currentSessionId,
-        ),
-        [sessions, currentSessionId],
-    );
-
-    const sessionPermissions = React.useMemo(() => {
-        if (scopedSessionIds.length === 0) return EMPTY_PERMISSIONS;
-        return flattenBlockingRequests(permissionsMap, scopedSessionIds);
-    }, [permissionsMap, scopedSessionIds]);
-
-    const sessionQuestions = React.useMemo(() => {
-        if (scopedSessionIds.length === 0) return EMPTY_QUESTIONS;
-        return flattenBlockingRequests(questionsMap, scopedSessionIds);
-    }, [questionsMap, scopedSessionIds]);
     const sessionIsWorking = React.useMemo(() => {
         if (!currentSessionId || sessionPermissions.length > 0 || sessionQuestions.length > 0) {
             return false;
@@ -561,15 +526,7 @@ export const ChatContainer: React.FC<ChatContainerProps> = ({ autoOpenDraft = tr
         return project ? getProjectDisplayLabel(project) : null;
     }, [activeProjectId, newSessionDraft?.selectedProjectId, projects]);
 
-    const parentSession = React.useMemo(() => {
-        if (!currentSessionId) return null;
-        const current = sessions.find((session) => session.id === currentSessionId);
-        const parentID = current?.parentID;
-        if (!parentID) return null;
-        return sessions.find((session) => session.id === parentID)
-            ?? getAllSyncSessions().find((session) => session.id === parentID)
-            ?? null;
-    }, [currentSessionId, sessions]);
+    const parentSession = useParentSession(currentSessionId, effectiveSessionDirectory);
 
     const handleReturnToParentSession = React.useCallback(() => {
         if (!parentSession) return;
@@ -943,6 +900,7 @@ export const ChatContainer: React.FC<ChatContainerProps> = ({ autoOpenDraft = tr
                 isDesktopExpandedInput={isDesktopExpandedInput}
                 isMobile={isMobile}
                 stickyUserHeader={stickyUserHeader}
+                directory={effectiveSessionDirectory}
                 scrollRef={scrollRef}
                 messageListRef={messageListRef}
                 pendingRevealWork={timelineController.pendingRevealWork}
diff --git a/packages/ui/src/components/chat/ChatInput.tsx b/packages/ui/src/components/chat/ChatInput.tsx
index c1381851..51ab068f 100644
--- a/packages/ui/src/components/chat/ChatInput.tsx
+++ b/packages/ui/src/components/chat/ChatInput.tsx
@@ -74,6 +74,7 @@ import { sessionEvents } from '@/lib/sessionEvents';
 import { fetchResponseStyleInstruction } from '@/lib/responseStyle';
 import { wrapSystemReminder } from '@/lib/systemReminder';
 import { getSyncMessages } from '@/sync/sync-refs';
+import { EMPTY_REVERTED_MESSAGE_DOCK_STATE, buildRevertedMessageDockState, type RevertedMessageDockState } from './revertedMessageDockState';
 import { eventMatchesShortcut, getEffectiveShortcutCombo, normalizeCombo } from '@/lib/shortcuts';
 import { isSyntheticPart } from '@/lib/messages/synthetic';
 import {
@@ -89,11 +90,10 @@ import {
     buildAttachmentCitationText,
     findAttachmentCitationRanges,
 } from './attachmentCitations';
-import type { Message, Part } from '@opencode-ai/sdk/v2/client';
+import type { Part } from '@opencode-ai/sdk/v2/client';
 
 const MAX_VISIBLE_TEXTAREA_LINES = 8;
 const EMPTY_QUEUE: QueuedMessage[] = [];
-const EMPTY_MESSAGES: Message[] = [];
 const FILE_MENTION_TOKEN = /^@[^\s]+$/;
 // Single-line URL pasted over a selection becomes a markdown link.
 const PASTE_LINK_URL_PATTERN = /^(https?:\/\/|mailto:)\S+$/i;
@@ -363,34 +363,28 @@ const RevertedMessageDock: React.FC<RevertedMessageDockProps> = React.memo(({ se
     const [restoringId, setRestoringId] = React.useState<string | null>(null);
     const [forkingId, setForkingId] = React.useState<string | null>(null);
     const [collapsed, setCollapsed] = React.useState(true);
-    const revertMessageID = useDirectorySync(
+    const revertedStateRef = React.useRef<RevertedMessageDockState>(EMPTY_REVERTED_MESSAGE_DOCK_STATE);
+    const revertedState = useDirectorySync(
         React.useCallback((state) => {
-            if (!sessionId) return undefined;
-            const session = state.session.find((item) => item.id === sessionId);
-            return (session as { revert?: { messageID?: string } } | undefined)?.revert?.messageID;
+            const next = buildRevertedMessageDockState(state, sessionId, revertedStateRef.current);
+            revertedStateRef.current = next;
+            return next;
         }, [sessionId]),
         directory,
     );
-    const sessionMessages = useDirectorySync(
-        React.useCallback((state) => (sessionId ? state.message[sessionId] ?? EMPTY_MESSAGES : EMPTY_MESSAGES), [sessionId]),
-        directory,
-    );
-    const partsByMessage = useDirectorySync(React.useCallback((state) => state.part, []), directory);
-
+    const revertMessageID = revertedState.revertMessageID;
     const userMessages = React.useMemo(
-        () => sessionMessages.filter((message): message is Message & { role: 'user' } => message.role === 'user'),
-        [sessionMessages],
+        () => revertedState.records.map((record) => record.message),
+        [revertedState],
     );
     const noTextContent = t('chat.revertPopover.noTextContent');
     const items = React.useMemo(() => {
         if (!revertMessageID) return [];
-        return userMessages
-            .filter((message) => message.id >= revertMessageID)
-            .map((message) => ({
-                id: message.id,
-                text: getRevertedPreview(partsByMessage[message.id] ?? [], noTextContent),
-            }));
-    }, [noTextContent, partsByMessage, revertMessageID, userMessages]);
+        return revertedState.records.map((record) => ({
+            id: record.message.id,
+            text: getRevertedPreview(record.parts, noTextContent),
+        }));
+    }, [noTextContent, revertMessageID, revertedState]);
     const firstRevertedMessageId = items[0]?.id;
 
     React.useEffect(() => {
diff --git a/packages/ui/src/components/chat/MarkdownRendererImpl.tsx b/packages/ui/src/components/chat/MarkdownRendererImpl.tsx
index 1b91a5db..b050fd25 100644
--- a/packages/ui/src/components/chat/MarkdownRendererImpl.tsx
+++ b/packages/ui/src/components/chat/MarkdownRendererImpl.tsx
@@ -1,5 +1,4 @@
 import React from 'react';
-import 'katex/dist/katex.min.css';
 import morphdom from 'morphdom';
 import { renderMermaidASCII, renderMermaidSVG } from 'beautiful-mermaid';
 import type { Part } from '@opencode-ai/sdk/v2';
@@ -19,7 +18,7 @@ import type { EditorAPI } from '@/lib/api/types';
 import { isDesktopLocalOriginActive, isDesktopShell, isVSCodeRuntime } from '@/lib/desktop';
 import { ensureOutsideFileGrantForDesktop } from '@/lib/outsideFileGrants';
 import { getDirectoryForFilePath, isAbsoluteFilePath, isFilePathWithinDirectory, normalizeFilePath, toAbsoluteFilePath } from '@/lib/path-utils';
-import { fallbackHtml, renderMarkdownBlocks } from './markdown/markdownCore';
+import { renderMarkdownBlocks, renderMarkdownSync } from './markdown/markdownCore';
 import { ensureMarkdownShikiTheme, getMarkdownSyntaxVars } from './markdown/markdownTheme';
 import {
   attachMarkdownInteractions,
@@ -1032,10 +1031,16 @@ const useMorphdomMarkdown = ({
       // `display:contents` keeps margin-collapsing/spacing identical to a flat
       // HTML body — the wrapper exists only for per-block reconciliation.
       block.style.display = 'contents';
-      block.innerHTML = fallbackHtml(text);
+      block.innerHTML = renderMarkdownSync(text);
+      // Decorate synchronously too: wrap code blocks in their framed card,
+      // mark inline code, build table controls, etc. The async pass re-decorates
+      // its own DOM before morphing, so without this the first paint shows bare
+      // <pre>/tables that "snap" into their decorated form a tick later. Matching
+      // the structure here keeps the async morph to syntax colors only.
+      decorateMarkdown(block, ctx);
       target.appendChild(block);
     }
-  }, [containerRef, text]);
+  }, [containerRef, text, ctx]);
 
   React.useEffect(() => {
     const container = containerRef.current;
diff --git a/packages/ui/src/components/chat/MessageList.tsx b/packages/ui/src/components/chat/MessageList.tsx
index 2489c2a4..8957f216 100644
--- a/packages/ui/src/components/chat/MessageList.tsx
+++ b/packages/ui/src/components/chat/MessageList.tsx
@@ -6,19 +6,19 @@ import ChatMessage from './ChatMessage';
 import { areOptionalRenderRelevantMessagesEqual, areRelevantTurnGroupingContextsEqual, areRenderRelevantMessagesEqual } from './message/renderCompare';
 import TurnItem from './components/TurnItem';
 import type { AnimationHandlers, ContentChangeReason } from '@/hooks/useChatAutoFollow';
-import { filterSyntheticParts } from '@/lib/messages/synthetic';
 import type { ChatMessageEntry, TurnRecord, TurnGroupingContext } from './lib/turns/types';
 import { useTurnRecords } from './hooks/useTurnRecords';
 import { applyRetryOverlay } from './lib/turns/applyRetryOverlay';
+import { buildLiveStreamingEntry } from './lib/turns/streamingTailEntry';
+import { getNormalizedMessageForDisplay, hasCompactionPart } from './lib/messageDisplayNormalization';
 import { useUIStore } from '@/stores/useUIStore';
 import { FadeInDisabledProvider } from './message/FadeInOnReveal';
 import { hasPendingUserSendAnimation, consumePendingUserSendAnimation } from '@/lib/userSendAnimation';
 import { streamPerfCount, streamPerfMeasure } from '@/stores/utils/streamDebug';
 import type { StreamPhase } from './message/types';
-import { normalizeParts } from './message/partUtils';
 import { useGlobalSessionsStore } from '@/stores/useGlobalSessionsStore';
-import { getReviewTransferDirection, type ReviewTransferDirection } from '@/lib/reviewFlow';
-import { getOriginalSessionID, getReviewSessionID } from '@/lib/sessionReviewMetadata';
+import { useSessionParts } from '@/sync/sync-context';
+import type { ReviewTransferDirection } from '@/lib/reviewFlow';
 
 const MESSAGE_LIST_VIRTUALIZE_THRESHOLD = 5;
 const EMPTY_STATIC_ENTRY_MESSAGES: ChatMessageEntry[] = [];
@@ -88,13 +88,6 @@ const resolveMessageRole = (message: ChatMessageEntry): string | null => {
         ?? null;
 };
 
-const hasCompactionPart = (message: ChatMessageEntry): boolean => {
-    return message.parts.some((part) => {
-        const type = (part as { type?: unknown } | null | undefined)?.type;
-        return type === 'compaction';
-    });
-};
-
 const getPartText = (part: Part): string => {
     const text = (part as { text?: unknown }).text;
     if (typeof text === 'string') {
@@ -107,40 +100,6 @@ const getPartText = (part: Part): string => {
     return '';
 };
 
-const normalizeCompactionCommandMessage = (message: ChatMessageEntry): ChatMessageEntry => {
-    if (!hasCompactionPart(message)) {
-        return message;
-    }
-
-    let changedParts = false;
-    const nextParts = message.parts.map((part) => {
-        const type = (part as { type?: unknown } | null | undefined)?.type;
-        if (type !== 'compaction') {
-            return part;
-        }
-        changedParts = true;
-        return { type: 'text', text: '/compact' } as Part;
-    });
-
-    const info = message.info as unknown as { clientRole?: string | null | undefined };
-    const needsClientRole = info.clientRole !== 'user';
-
-    if (!changedParts && !needsClientRole) {
-        return message;
-    }
-
-    return {
-        ...message,
-        info: needsClientRole
-            ? ({
-                ...(message.info as unknown as Record<string, unknown>),
-                clientRole: 'user',
-            } as unknown as typeof message.info)
-            : message.info,
-        parts: changedParts ? nextParts : message.parts,
-    };
-};
-
 const normalizeCompactionSummaryMessage = (
     message: ChatMessageEntry,
     compactionCommandIds: Set<string>,
@@ -391,39 +350,6 @@ const withShellBridgeDetails = (message: ChatMessageEntry, details: ShellBridgeD
     };
 };
 
-const normalizeMessageParts = (message: ChatMessageEntry): ChatMessageEntry => {
-    const parts = normalizeParts(message.parts);
-    if (parts.length === message.parts.length) {
-        return message;
-    }
-    return {
-        ...message,
-        parts,
-    };
-};
-
-const normalizedMessageBySource = new WeakMap<ChatMessageEntry, ChatMessageEntry>();
-
-const getNormalizedMessageForDisplay = (message: ChatMessageEntry): ChatMessageEntry => {
-    const cached = normalizedMessageBySource.get(message);
-    if (cached) {
-        return cached;
-    }
-
-    const normalizedPartMessage = normalizeMessageParts(message);
-    const normalizedCompactionMessage = normalizeCompactionCommandMessage(normalizedPartMessage);
-    const filteredParts = filterSyntheticParts(normalizedCompactionMessage.parts);
-    const normalized = filteredParts === normalizedCompactionMessage.parts
-        ? normalizedCompactionMessage
-        : {
-            ...normalizedCompactionMessage,
-            parts: filteredParts,
-        };
-
-    normalizedMessageBySource.set(message, normalized);
-    return normalized;
-};
-
 interface MessageListProps {
     sessionKey: string;
     disableStaging?: boolean;
@@ -442,6 +368,7 @@ interface MessageListProps {
     isLoadingOlder: boolean;
     scrollToBottom?: () => void;
     scrollRef?: React.RefObject<HTMLDivElement | null>;
+    directory?: string;
 }
 
 export interface MessageListHandle {
@@ -1007,11 +934,10 @@ type StaticHistoryListProps = {
     chatRenderMode: 'sorted' | 'live';
     shouldAnimateUserMessage: (message: ChatMessageEntry) => boolean;
     onUserAnimationConsumed: (messageId: string) => void;
-    activeStreamingPhase?: StreamPhase | null;
     reviewTransferDirection?: ReviewTransferDirection | null;
 };
 
-const StaticHistoryList = React.memo(({ entries, shouldVirtualize, contentRef, scrollRef, virtualizerRef, virtualizerKey, virtualCache, shift, onMessageContentChange, getAnimationHandlers, scrollToBottom, stickyUserHeader, defaultActivityExpanded, turnUiStates, onToggleTurnGroup, chatRenderMode, shouldAnimateUserMessage, onUserAnimationConsumed, activeStreamingPhase, reviewTransferDirection }: StaticHistoryListProps) => {
+const StaticHistoryList = React.memo(({ entries, shouldVirtualize, contentRef, scrollRef, virtualizerRef, virtualizerKey, virtualCache, shift, onMessageContentChange, getAnimationHandlers, scrollToBottom, stickyUserHeader, defaultActivityExpanded, turnUiStates, onToggleTurnGroup, chatRenderMode, shouldAnimateUserMessage, onUserAnimationConsumed, reviewTransferDirection }: StaticHistoryListProps) => {
     const renderEntry = React.useCallback((entry: RenderEntry) => {
         return (
             <MessageListEntry
@@ -1029,11 +955,11 @@ const StaticHistoryList = React.memo(({ entries, shouldVirtualize, contentRef, s
                 shouldAnimateUserMessage={shouldAnimateUserMessage}
                 onUserAnimationConsumed={onUserAnimationConsumed}
                 activeStreamingMessageId={null}
-                activeStreamingPhase={activeStreamingPhase}
+                activeStreamingPhase={null}
                 reviewTransferDirection={reviewTransferDirection}
             />
         );
-    }, [activeStreamingPhase, chatRenderMode, defaultActivityExpanded, getAnimationHandlers, onMessageContentChange, onToggleTurnGroup, onUserAnimationConsumed, reviewTransferDirection, scrollToBottom, shouldAnimateUserMessage, stickyUserHeader, turnUiStates]);
+    }, [chatRenderMode, defaultActivityExpanded, getAnimationHandlers, onMessageContentChange, onToggleTurnGroup, onUserAnimationConsumed, reviewTransferDirection, scrollToBottom, shouldAnimateUserMessage, stickyUserHeader, turnUiStates]);
 
     if (!shouldVirtualize) {
         return (
@@ -1074,6 +1000,7 @@ StaticHistoryList.displayName = 'StaticHistoryList';
 
 const StreamingTailContent: React.FC<{
     entry: RenderEntry;
+    directory?: string;
     onMessageContentChange: (reason?: ContentChangeReason) => void;
     getAnimationHandlers: (messageId: string) => AnimationHandlers;
     scrollToBottom?: () => void;
@@ -1083,6 +1010,7 @@ const StreamingTailContent: React.FC<{
     turnUiStates: Map<string, TurnUiState>;
     onToggleTurnGroup: (turnId: string) => void;
     chatRenderMode: 'sorted' | 'live';
+    showTurnChangedFiles: boolean;
     shouldAnimateUserMessage: (message: ChatMessageEntry) => boolean;
     onUserAnimationConsumed: (messageId: string) => void;
     activeStreamingMessageId?: string | null;
@@ -1090,6 +1018,7 @@ const StreamingTailContent: React.FC<{
     reviewTransferDirection?: ReviewTransferDirection | null;
 }> = ({
     entry,
+    directory,
     onMessageContentChange,
     getAnimationHandlers,
     scrollToBottom,
@@ -1099,15 +1028,24 @@ const StreamingTailContent: React.FC<{
     turnUiStates,
     onToggleTurnGroup,
     chatRenderMode,
+    showTurnChangedFiles,
     shouldAnimateUserMessage,
     onUserAnimationConsumed,
     activeStreamingMessageId,
     activeStreamingPhase,
     reviewTransferDirection,
 }) => {
+    const liveParts = useSessionParts(activeStreamingMessageId ?? '', directory);
+    const liveEntry = React.useMemo(() => buildLiveStreamingEntry(entry, {
+        activeStreamingMessageId,
+        liveParts,
+        showTextJustificationActivity: chatRenderMode === 'sorted',
+        showTurnChangedFiles,
+    }), [activeStreamingMessageId, chatRenderMode, entry, liveParts, showTurnChangedFiles]);
+
     return (
         <MessageListEntry
-            entry={entry}
+            entry={liveEntry}
             onMessageContentChange={onMessageContentChange}
             getAnimationHandlers={getAnimationHandlers}
             scrollToBottom={scrollToBottom}
@@ -1141,6 +1079,7 @@ const MessageList = React.forwardRef<MessageListHandle, MessageListProps>(({
     isLoadingOlder,
     scrollToBottom,
     scrollRef,
+    directory,
 }, ref) => {
     streamPerfCount('ui.message_list.render');
     const stickyUserHeader = useUIStore(state => state.stickyUserHeader);
@@ -1149,18 +1088,7 @@ const MessageList = React.forwardRef<MessageListHandle, MessageListProps>(({
     const showTurnChangedFiles = useUIStore((state) => state.showTurnChangedFiles);
     const defaultActivityExpanded = activityRenderMode === 'summary';
     const reviewTransferDirection = useGlobalSessionsStore((state) => {
-        const currentSession = state.activeSessions.find((session) => session.id === sessionKey);
-        const direction = getReviewTransferDirection(currentSession);
-        if (!currentSession || !direction) return null;
-
-        const targetSessionId = direction === 'review-to-original'
-            ? getOriginalSessionID(currentSession)
-            : getReviewSessionID(currentSession);
-        if (!targetSessionId) return null;
-
-        return state.activeSessions.some((session) => session.id === targetSessionId)
-            ? direction
-            : null;
+        return state.reviewTransferBySessionId.get(sessionKey) ?? null;
     });
     const [turnUiStates, setTurnUiStates] = React.useState<Map<string, TurnUiState>>(() => new Map());
     const userAnimationRef = React.useRef<{
@@ -1665,12 +1593,12 @@ const MessageList = React.forwardRef<MessageListHandle, MessageListProps>(({
                             chatRenderMode={chatRenderMode}
                             shouldAnimateUserMessage={shouldAnimateUserMessage}
                             onUserAnimationConsumed={onUserAnimationConsumed}
-                            activeStreamingPhase={activeStreamingPhase}
                             reviewTransferDirection={reviewTransferDirection}
                         />
                         {trailingStreamingEntry ? (
                             <StreamingTailContent
                                 entry={trailingStreamingEntry}
+                                directory={directory}
                                 onMessageContentChange={stableTailContentChange}
                                 getAnimationHandlers={stableGetAnimationHandlers}
                                 scrollToBottom={stableScrollToBottom}
@@ -1680,6 +1608,7 @@ const MessageList = React.forwardRef<MessageListHandle, MessageListProps>(({
                                 turnUiStates={turnUiStates}
                                 onToggleTurnGroup={toggleTurnGroup}
                                 chatRenderMode={chatRenderMode}
+                                showTurnChangedFiles={showTurnChangedFiles}
                                 shouldAnimateUserMessage={shouldAnimateUserMessage}
                                 onUserAnimationConsumed={onUserAnimationConsumed}
                                 activeStreamingMessageId={activeStreamingMessageId}
diff --git a/packages/ui/src/components/chat/hooks/useChatTimelineController.ts b/packages/ui/src/components/chat/hooks/useChatTimelineController.ts
index 5af98f8f..cf437015 100644
--- a/packages/ui/src/components/chat/hooks/useChatTimelineController.ts
+++ b/packages/ui/src/components/chat/hooks/useChatTimelineController.ts
@@ -334,24 +334,67 @@ export const useChatTimelineController = ({
         return messageListRef.current?.restoreViewportAnchor(anchor) ?? false;
     }, [messageListRef]);
 
+    // Tracks the timeline edges + height of the previous commit so a prepend
+    // that did NOT go through fetchOlderHistory (e.g. the background history
+    // prepend dispatched from useSync) can be compensated too. With
+    // overflow-anchor:none the browser leaves scrollTop unchanged when content
+    // is inserted above, so without this the viewport visibly jumps and
+    // auto-follow yanks it back on the next frame — a one-shot up/down judder.
+    const prependTrackingRef = React.useRef<{
+        oldestId: string | null;
+        newestId: string | null;
+        scrollHeight: number;
+    } | null>(null);
+
     React.useLayoutEffect(() => {
-        const snap = prePrependScrollRef.current;
         const container = scrollRef.current;
-        if (!snap || !container) return;
-        prePrependScrollRef.current = null;
+        if (!container) return;
 
-        // When a viewport anchor is available, delegate to MessageList
-        // restoreViewportAnchor which falls back to virtualizer-aware
-        // scrollHistoryIndexIntoView when the element is not in the DOM.
-        if (snap.anchor && restoreViewportAnchor(snap.anchor)) {
-            return;
+        const snap = prePrependScrollRef.current;
+        if (snap) {
+            prePrependScrollRef.current = null;
+            // When a viewport anchor is available, delegate to MessageList
+            // restoreViewportAnchor which falls back to virtualizer-aware
+            // scrollHistoryIndexIntoView when the element is not in the DOM.
+            if (!(snap.anchor && restoreViewportAnchor(snap.anchor))) {
+                // Fallback: height-delta compensation
+                const delta = container.scrollHeight - snap.height;
+                if (delta > 0) {
+                    container.scrollTop = snap.top + delta;
+                }
+            }
+        } else {
+            // Auto-detect a prepend: the oldest message changed while the newest
+            // stayed the same (distinguishes a real prepend from a session
+            // switch, a bottom append, or a streaming part growing). Compensate
+            // synchronously by the exact height delta — for a bottom-pinned
+            // viewport this keeps it pinned, for a released one it preserves the
+            // read position, with no intermediate frame for auto-follow to fight.
+            const prev = prependTrackingRef.current;
+            const currentOldestId = renderedMessages[0]?.info?.id ?? null;
+            const currentNewestId = renderedMessages[renderedMessages.length - 1]?.info?.id ?? null;
+            const isPrepend = Boolean(
+                prev
+                && prev.oldestId
+                && currentOldestId
+                && currentOldestId !== prev.oldestId
+                && prev.newestId
+                && currentNewestId
+                && currentNewestId === prev.newestId,
+            );
+            if (isPrepend && prev) {
+                const delta = container.scrollHeight - prev.scrollHeight;
+                if (delta > 0) {
+                    container.scrollTop = container.scrollTop + delta;
+                }
+            }
         }
 
-        // Fallback: height-delta compensation
-        const delta = container.scrollHeight - snap.height;
-        if (delta > 0) {
-            container.scrollTop = snap.top + delta;
-        }
+        prependTrackingRef.current = {
+            oldestId: renderedMessages[0]?.info?.id ?? null,
+            newestId: renderedMessages[renderedMessages.length - 1]?.info?.id ?? null,
+            scrollHeight: container.scrollHeight,
+        };
     }, [renderedMessages, scrollRef, restoreViewportAnchor]);
 
     const revealBufferedTurns = React.useCallback(async (): Promise<boolean> => false, []);
diff --git a/packages/ui/src/components/chat/hooks/useTurnRecords.ts b/packages/ui/src/components/chat/hooks/useTurnRecords.ts
index 9538db37..a7b94938 100644
--- a/packages/ui/src/components/chat/hooks/useTurnRecords.ts
+++ b/packages/ui/src/components/chat/hooks/useTurnRecords.ts
@@ -1,6 +1,7 @@
 import React from 'react';
 import { projectTurnRecords } from '../lib/turns/projectTurnRecords';
 import type { ChatMessageEntry, TurnProjectionResult, TurnRecord } from '../lib/turns/types';
+import { buildProjectionCacheKey, getCachedProjection, setCachedProjection } from '../lib/turns/turnProjectionCache';
 import { streamPerfMeasure } from '@/stores/utils/streamDebug';
 
 interface UseTurnRecordsOptions {
@@ -46,6 +47,18 @@ export const useTurnRecords = (
     }, [options.sessionKey, options.showTextJustificationActivity, options.showTurnChangedFiles]);
 
     const projection = React.useMemo(() => {
+        const sessionKey = options.sessionKey ?? '';
+        const cached = getCachedProjection(
+            sessionKey,
+            messages,
+            options.showTextJustificationActivity,
+            options.showTurnChangedFiles,
+        );
+        if (cached) {
+            previousProjectionRef.current = cached;
+            return cached;
+        }
+
         return streamPerfMeasure('ui.turns.projection_ms', () => {
             const nextProjection = projectTurnRecords(messages, {
                 previousProjection: previousProjectionRef.current,
@@ -53,9 +66,18 @@ export const useTurnRecords = (
                 showTurnChangedFiles: options.showTurnChangedFiles,
             });
             previousProjectionRef.current = nextProjection;
+
+            const cacheKey = buildProjectionCacheKey(
+                sessionKey,
+                messages,
+                options.showTextJustificationActivity,
+                options.showTurnChangedFiles,
+            );
+            setCachedProjection(cacheKey, nextProjection);
+
             return nextProjection;
         });
-    }, [messages, options.showTextJustificationActivity, options.showTurnChangedFiles]);
+    }, [messages, options.showTextJustificationActivity, options.showTurnChangedFiles, options.sessionKey]);
 
     const staticTurns = React.useMemo(() => {
         const nextStatic = projection.turns.length <= 1
diff --git a/packages/ui/src/components/chat/lib/messageDisplayNormalization.ts b/packages/ui/src/components/chat/lib/messageDisplayNormalization.ts
new file mode 100644
index 00000000..85a862c3
--- /dev/null
+++ b/packages/ui/src/components/chat/lib/messageDisplayNormalization.ts
@@ -0,0 +1,79 @@
+import type { Part } from '@opencode-ai/sdk/v2';
+
+import { filterSyntheticParts } from '@/lib/messages/synthetic';
+import { normalizeParts } from '../message/partUtils';
+import type { ChatMessageEntry } from './turns/types';
+
+export const hasCompactionPart = (message: ChatMessageEntry): boolean => {
+    return message.parts.some((part) => {
+        const type = (part as { type?: unknown } | null | undefined)?.type;
+        return type === 'compaction';
+    });
+};
+
+const normalizeCompactionCommandMessage = (message: ChatMessageEntry): ChatMessageEntry => {
+    if (!hasCompactionPart(message)) {
+        return message;
+    }
+
+    let changedParts = false;
+    const nextParts = message.parts.map((part) => {
+        const type = (part as { type?: unknown } | null | undefined)?.type;
+        if (type !== 'compaction') {
+            return part;
+        }
+        changedParts = true;
+        return { type: 'text', text: '/compact' } as Part;
+    });
+
+    const info = message.info as unknown as { clientRole?: string | null | undefined };
+    const needsClientRole = info.clientRole !== 'user';
+
+    if (!changedParts && !needsClientRole) {
+        return message;
+    }
+
+    return {
+        ...message,
+        info: needsClientRole
+            ? ({
+                ...(message.info as unknown as Record<string, unknown>),
+                clientRole: 'user',
+            } as unknown as typeof message.info)
+            : message.info,
+        parts: changedParts ? nextParts : message.parts,
+    };
+};
+
+const normalizeMessageParts = (message: ChatMessageEntry): ChatMessageEntry => {
+    const parts = normalizeParts(message.parts);
+    if (parts.length === message.parts.length) {
+        return message;
+    }
+    return {
+        ...message,
+        parts,
+    };
+};
+
+const normalizedMessageBySource = new WeakMap<ChatMessageEntry, ChatMessageEntry>();
+
+export const getNormalizedMessageForDisplay = (message: ChatMessageEntry): ChatMessageEntry => {
+    const cached = normalizedMessageBySource.get(message);
+    if (cached) {
+        return cached;
+    }
+
+    const normalizedPartMessage = normalizeMessageParts(message);
+    const normalizedCompactionMessage = normalizeCompactionCommandMessage(normalizedPartMessage);
+    const filteredParts = filterSyntheticParts(normalizedCompactionMessage.parts);
+    const normalized = filteredParts === normalizedCompactionMessage.parts
+        ? normalizedCompactionMessage
+        : {
+            ...normalizedCompactionMessage,
+            parts: filteredParts,
+        };
+
+    normalizedMessageBySource.set(message, normalized);
+    return normalized;
+};
diff --git a/packages/ui/src/components/chat/lib/turns/projectTurnRecords.test.ts b/packages/ui/src/components/chat/lib/turns/projectTurnRecords.test.ts
index 20f94859..6eb32053 100644
--- a/packages/ui/src/components/chat/lib/turns/projectTurnRecords.test.ts
+++ b/packages/ui/src/components/chat/lib/turns/projectTurnRecords.test.ts
@@ -106,6 +106,27 @@ describe('projectTurnRecords', () => {
         expect(next.turns[1]).not.toBe(initial.turns[1]);
     });
 
+    test('hydrates updated turns when a previous projection exists but no turn is reusable', () => {
+        const user = createMessageEntry({ id: 'u1', role: 'user', createdAt: 1 });
+        const assistant = createMessageEntry({ id: 'a1', role: 'assistant', parentID: 'u1', createdAt: 2 });
+        const initial = projectTurnRecords([user, assistant]);
+        const updatedAssistant = {
+            ...assistant,
+            parts: [{ id: 'tool_1', type: 'tool', tool: 'bash', state: { status: 'completed' } } as Part],
+        };
+
+        const next = projectTurnRecords([user, updatedAssistant], {
+            previousProjection: initial,
+        });
+
+        expect(next.turns).toHaveLength(1);
+        expect(next.turns[0]).not.toBe(initial.turns[0]);
+        expect(next.turns[0]?.hasTools).toBe(true);
+        expect(next.turns[0]?.activityParts).toHaveLength(1);
+        expect(next.turns[0]?.stream.isStreaming).toBe(true);
+        expect(next.turns[0]?.stream.isRetrying).toBe(false);
+    });
+
     test('reuses the whole turns array when every turn is unchanged', () => {
         const user = createMessageEntry({ id: 'u1', role: 'user', createdAt: 1 });
         const assistant = createMessageEntry({ id: 'a1', role: 'assistant', parentID: 'u1', createdAt: 2 });
diff --git a/packages/ui/src/components/chat/lib/turns/projectTurnRecords.ts b/packages/ui/src/components/chat/lib/turns/projectTurnRecords.ts
index d9eb27dc..bdff1b45 100644
--- a/packages/ui/src/components/chat/lib/turns/projectTurnRecords.ts
+++ b/packages/ui/src/components/chat/lib/turns/projectTurnRecords.ts
@@ -115,12 +115,43 @@ const canReusePreviousTurn = (previous: TurnRecord, next: TurnRecord): boolean =
         && areSameMessageRefs(previous.assistantMessages, next.assistantMessages);
 };
 
-const stabilizeTurnRecords = (
+const hydrateTurnRecord = (
+    turn: TurnRecord,
+    effectiveOptions: ProjectTurnRecordsOptions,
+): TurnRecord => {
+    turn.summary = projectTurnSummary(turn.assistantMessages);
+    turn.summaryText = turn.summary.text ?? getUserSummaryBody(turn.userMessage);
+    turn.diffStats = projectTurnDiffStats(turn.userMessage);
+    turn.changedFiles = effectiveOptions.showTurnChangedFiles
+        ? projectTurnChangedFiles(turn.userMessage)
+        : undefined;
+
+    const activity = projectTurnActivity({
+        turnId: turn.turnId,
+        assistantMessages: turn.assistantMessages,
+        summarySourceMessageId: turn.summary.sourceMessageId,
+        summarySourcePartId: turn.summary.sourcePartId,
+        showTextJustificationActivity: effectiveOptions.showTextJustificationActivity,
+    });
+    turn.activityParts = activity.activityParts;
+    turn.activitySegments = activity.activitySegments;
+    turn.hasTools = activity.hasTools;
+    turn.hasReasoning = activity.hasReasoning;
+
+    turn.stream = buildTurnStreamState(turn.userMessage, turn.assistantMessages);
+    turn.startedAt = turn.stream.startedAt;
+    turn.completedAt = turn.stream.completedAt;
+    turn.durationMs = turn.stream.durationMs;
+    return turn;
+};
+
+const hydrateStableTurnRecords = (
     turns: TurnRecord[],
-    previousProjection?: TurnProjectionResult | null,
+    effectiveOptions: ProjectTurnRecordsOptions,
 ): TurnRecord[] => {
+    const previousProjection = effectiveOptions.previousProjection;
     if (!previousProjection || previousProjection.turns.length === 0 || turns.length === 0) {
-        return turns;
+        return turns.map((turn) => hydrateTurnRecord(turn, effectiveOptions));
     }
 
     let canReuseTurnArray = previousProjection.turns.length === turns.length;
@@ -137,14 +168,14 @@ const stabilizeTurnRecords = (
         }
 
         canReuseTurnArray = false;
-        return turn;
+        return hydrateTurnRecord(turn, effectiveOptions);
     });
 
     if (canReuseTurnArray && reusedAnyTurn) {
         return previousProjection.turns;
     }
 
-    return reusedAnyTurn ? nextTurns : turns;
+    return nextTurns;
 };
 
 export const projectTurnRecords = (
@@ -214,33 +245,7 @@ export const projectTurnRecords = (
         groupedMessageIds.add(message.info.id);
     });
 
-    turns.forEach((turn) => {
-        turn.summary = projectTurnSummary(turn.assistantMessages);
-        turn.summaryText = turn.summary.text ?? getUserSummaryBody(turn.userMessage);
-        turn.diffStats = projectTurnDiffStats(turn.userMessage);
-        turn.changedFiles = effectiveOptions.showTurnChangedFiles
-            ? projectTurnChangedFiles(turn.userMessage)
-            : undefined;
-
-        const activity = projectTurnActivity({
-            turnId: turn.turnId,
-            assistantMessages: turn.assistantMessages,
-            summarySourceMessageId: turn.summary.sourceMessageId,
-            summarySourcePartId: turn.summary.sourcePartId,
-            showTextJustificationActivity: effectiveOptions.showTextJustificationActivity,
-        });
-        turn.activityParts = activity.activityParts;
-        turn.activitySegments = activity.activitySegments;
-        turn.hasTools = activity.hasTools;
-        turn.hasReasoning = activity.hasReasoning;
-
-        turn.stream = buildTurnStreamState(turn.userMessage, turn.assistantMessages);
-        turn.startedAt = turn.stream.startedAt;
-        turn.completedAt = turn.stream.completedAt;
-        turn.durationMs = turn.stream.durationMs;
-    });
-
-    const stableTurns = stabilizeTurnRecords(turns, effectiveOptions.previousProjection);
+    const stableTurns = hydrateStableTurnRecords(turns, effectiveOptions);
     const projection = projectTurnIndexes(stableTurns);
     const ungroupedMessageIds = new Set<string>();
     messages.forEach((message) => {
diff --git a/packages/ui/src/components/chat/lib/turns/streamingTailEntry.test.ts b/packages/ui/src/components/chat/lib/turns/streamingTailEntry.test.ts
new file mode 100644
index 00000000..ed674707
--- /dev/null
+++ b/packages/ui/src/components/chat/lib/turns/streamingTailEntry.test.ts
@@ -0,0 +1,134 @@
+import { describe, expect, test } from 'bun:test';
+import type { Message, Part } from '@opencode-ai/sdk/v2';
+
+import { buildLiveStreamingEntry, type StreamingTailEntry } from './streamingTailEntry';
+import type { ChatMessageEntry, TurnRecord } from './types';
+
+const message = (id: string, role: 'user' | 'assistant', parentID?: string, parts: Part[] = []): ChatMessageEntry => ({
+    info: {
+        id,
+        role,
+        sessionID: 'ses_1',
+        ...(parentID ? { parentID } : {}),
+        time: { created: 1 },
+    } as Message,
+    parts,
+});
+
+const textPart = (id: string, text: string): Part => ({
+    id,
+    type: 'text',
+    text,
+} as Part);
+
+const syntheticTextPart = (id: string, text: string): Part => ({
+    id,
+    type: 'text',
+    text,
+    synthetic: true,
+} as Part);
+
+const reasoningPart = (id: string, text: string): Part => ({
+    id,
+    type: 'reasoning',
+    text,
+} as Part);
+
+const turnEntry = (assistant: ChatMessageEntry): StreamingTailEntry => {
+    const user = message('user_1', 'user');
+    return {
+        kind: 'turn',
+        key: 'turn:user_1',
+        isLastTurn: true,
+        turn: {
+            turnId: 'user_1',
+            userMessageId: 'user_1',
+            userMessage: user,
+            headerMessageId: assistant.info.id,
+            messages: [],
+            assistantMessageIds: [assistant.info.id],
+            assistantMessages: [assistant],
+            activityParts: [],
+            activitySegments: [],
+            summary: {},
+            hasTools: false,
+            hasReasoning: false,
+            stream: { isStreaming: true, isRetrying: false },
+        } satisfies TurnRecord,
+    };
+};
+
+describe('buildLiveStreamingEntry', () => {
+    test('returns the same entry when the active message is not in the tail', () => {
+        const assistant = message('assistant_1', 'assistant', 'user_1', [textPart('part_1', 'old')]);
+        const entry = turnEntry(assistant);
+
+        const next = buildLiveStreamingEntry(entry, {
+            activeStreamingMessageId: 'assistant_other',
+            liveParts: [textPart('part_live', 'live')],
+            showTextJustificationActivity: true,
+            showTurnChangedFiles: false,
+        });
+
+        expect(next).toBe(entry);
+    });
+
+    test('rebuilds only the streaming turn with live parts', () => {
+        const assistant = message('assistant_1', 'assistant', 'user_1', [textPart('part_1', 'hel')]);
+        const entry = turnEntry(assistant);
+        const liveParts = [reasoningPart('part_1_live', 'thinking')];
+
+        const next = buildLiveStreamingEntry(entry, {
+            activeStreamingMessageId: 'assistant_1',
+            liveParts,
+            showTextJustificationActivity: true,
+            showTurnChangedFiles: false,
+        });
+
+        expect(next).not.toBe(entry);
+        expect(next.kind).toBe('turn');
+        if (next.kind !== 'turn') return;
+        expect(next.turn.assistantMessages[0]?.parts).toBe(liveParts);
+        expect(next.turn.activityParts.length).toBeGreaterThan(0);
+    });
+
+    test('updates an ungrouped streaming message with live parts', () => {
+        const stale = message('assistant_1', 'assistant', undefined, [textPart('part_1', 'old')]);
+        const entry: StreamingTailEntry = {
+            kind: 'ungrouped',
+            key: 'msg:assistant_1',
+            message: stale,
+        };
+        const liveParts = [textPart('part_1_live', 'live')];
+
+        const next = buildLiveStreamingEntry(entry, {
+            activeStreamingMessageId: 'assistant_1',
+            liveParts,
+            showTextJustificationActivity: false,
+            showTurnChangedFiles: false,
+        });
+
+        expect(next).not.toBe(entry);
+        expect(next.kind).toBe('ungrouped');
+        if (next.kind !== 'ungrouped') return;
+        expect(next.message.parts).toBe(liveParts);
+    });
+
+    test('normalizes live tail parts with the display filtering path', () => {
+        const stale = message('assistant_1', 'assistant', 'user_1', [textPart('part_1', 'old')]);
+        const entry = turnEntry(stale);
+        const visible = textPart('part_visible', 'visible');
+        const synthetic = syntheticTextPart('part_synthetic', 'hidden while streaming');
+
+        const next = buildLiveStreamingEntry(entry, {
+            activeStreamingMessageId: 'assistant_1',
+            liveParts: [synthetic, visible],
+            showTextJustificationActivity: true,
+            showTurnChangedFiles: false,
+        });
+
+        expect(next.kind).toBe('turn');
+        if (next.kind !== 'turn') return;
+        expect(next.turn.assistantMessages[0]?.parts).toEqual([visible]);
+    });
+});
diff --git a/packages/ui/src/components/chat/lib/turns/streamingTailEntry.ts b/packages/ui/src/components/chat/lib/turns/streamingTailEntry.ts
new file mode 100644
index 00000000..b1564452
--- /dev/null
+++ b/packages/ui/src/components/chat/lib/turns/streamingTailEntry.ts
@@ -0,0 +1,86 @@
+import type { Part } from '@opencode-ai/sdk/v2';
+
+import { getNormalizedMessageForDisplay } from '../messageDisplayNormalization';
+import { projectTurnRecords } from './projectTurnRecords';
+import type { ChatMessageEntry, TurnRecord } from './types';
+
+export type StreamingTailEntry =
+    | {
+        kind: 'ungrouped';
+        key: string;
+        message: ChatMessageEntry;
+        previousMessage?: ChatMessageEntry;
+        nextMessage?: ChatMessageEntry;
+    }
+    | { kind: 'turn'; key: string; turn: TurnRecord; isLastTurn: boolean };
+
+type BuildLiveStreamingEntryOptions = {
+    activeStreamingMessageId: string | null | undefined;
+    liveParts: Part[];
+    showTextJustificationActivity: boolean;
+    showTurnChangedFiles: boolean;
+};
+
+const withLiveParts = (
+    message: ChatMessageEntry,
+    activeStreamingMessageId: string,
+    liveParts: Part[],
+): ChatMessageEntry => {
+    if (message.info.id !== activeStreamingMessageId || message.parts === liveParts) {
+        return message;
+    }
+
+    return getNormalizedMessageForDisplay({
+        ...message,
+        parts: liveParts,
+    });
+};
+
+export const buildLiveStreamingEntry = <TEntry extends StreamingTailEntry>(
+    entry: TEntry,
+    options: BuildLiveStreamingEntryOptions,
+): TEntry => {
+    const activeStreamingMessageId = options.activeStreamingMessageId;
+    if (!activeStreamingMessageId) {
+        return entry;
+    }
+
+    if (entry.kind === 'ungrouped') {
+        const message = withLiveParts(entry.message, activeStreamingMessageId, options.liveParts);
+        if (message === entry.message) {
+            return entry;
+        }
+        return {
+            ...entry,
+            message,
+        };
+    }
+
+    let changed = false;
+    const assistantMessages = entry.turn.assistantMessages.map((message) => {
+        const next = withLiveParts(message, activeStreamingMessageId, options.liveParts);
+        if (next !== message) {
+            changed = true;
+        }
+        return next;
+    });
+
+    if (!changed) {
+        return entry;
+    }
+
+    const projection = projectTurnRecords([entry.turn.userMessage, ...assistantMessages], {
+        showTextJustificationActivity: options.showTextJustificationActivity,
+        showTurnChangedFiles: options.showTurnChangedFiles,
+    });
+    const turn = projection.turns[0] ?? {
+        ...entry.turn,
+        assistantMessages,
+        assistantMessageIds: assistantMessages.map((message) => message.info.id),
+    };
+
+    return {
+        ...entry,
+        turn,
+    };
+};
diff --git a/packages/ui/src/components/chat/lib/turns/turnProjectionCache.test.ts b/packages/ui/src/components/chat/lib/turns/turnProjectionCache.test.ts
new file mode 100644
index 00000000..47471a9a
--- /dev/null
+++ b/packages/ui/src/components/chat/lib/turns/turnProjectionCache.test.ts
@@ -0,0 +1,35 @@
+import { describe, expect, test } from 'bun:test';
+import type { Message, Part } from '@opencode-ai/sdk/v2';
+import { buildProjectionCacheKey } from './turnProjectionCache';
+import type { ChatMessageEntry } from './types';
+
+const createEntry = (text: string): ChatMessageEntry => ({
+  info: { id: 'msg_1', role: 'assistant' } as Message,
+  parts: [{ id: 'prt_1', type: 'text', text } as Part],
+});
+
+describe('turnProjectionCache', () => {
+  test('keeps the cache key stable for unchanged message and part references', () => {
+    const messages = [createEntry('hello')];
+
+    const first = buildProjectionCacheKey('session_1', messages, false, false);
+    const second = buildProjectionCacheKey('session_1', messages, false, false);
+
+    expect(second).toBe(first);
+  });
+
+  test('changes the cache key when streaming replaces a part with the same id and count', () => {
+    const before = [createEntry('hel')];
+    const after = [
+      {
+        info: before[0].info,
+        parts: [{ id: 'prt_1', type: 'text', text: 'hello' } as Part],
+      },
+    ];
+
+    const beforeKey = buildProjectionCacheKey('session_1', before, false, false);
+    const afterKey = buildProjectionCacheKey('session_1', after, false, false);
+
+    expect(afterKey).not.toBe(beforeKey);
+  });
+});
diff --git a/packages/ui/src/components/chat/lib/turns/turnProjectionCache.ts b/packages/ui/src/components/chat/lib/turns/turnProjectionCache.ts
new file mode 100644
index 00000000..39c4c1ac
--- /dev/null
+++ b/packages/ui/src/components/chat/lib/turns/turnProjectionCache.ts
@@ -0,0 +1,86 @@
+import type { ChatMessageEntry, TurnProjectionResult } from './types';
+import { isVSCodeRuntime } from '@/lib/desktop';
+import { isMobileSurfaceRuntime } from '@/lib/runtimeSurface';
+
+const TURN_PROJECTION_CACHE_MAX = 30;
+const VSCODE_TURN_PROJECTION_CACHE_MAX = 4;
+const MOBILE_TURN_PROJECTION_CACHE_MAX = 4;
+
+const projectionCache = new Map<string, TurnProjectionResult>();
+const objectVersionByRef = new WeakMap<object, number>();
+let nextObjectVersion = 1;
+
+const getProjectionCacheMax = () => {
+  if (isVSCodeRuntime()) return VSCODE_TURN_PROJECTION_CACHE_MAX;
+  if (isMobileSurfaceRuntime()) return MOBILE_TURN_PROJECTION_CACHE_MAX;
+  return TURN_PROJECTION_CACHE_MAX;
+};
+
+const getObjectVersion = (value: object): number => {
+  const cached = objectVersionByRef.get(value);
+  if (cached !== undefined) return cached;
+  const next = nextObjectVersion;
+  nextObjectVersion += 1;
+  objectVersionByRef.set(value, next);
+  return next;
+};
+
+const buildMessagesVersionSignature = (messages: ChatMessageEntry[]): string => {
+  return messages.map((message) => {
+    const infoVersion = getObjectVersion(message.info as object);
+    const partsVersion = getObjectVersion(message.parts);
+    const partVersions = message.parts.map((part) => getObjectVersion(part as object)).join(',');
+    return `${infoVersion}:${partsVersion}:${partVersions}`;
+  }).join(';');
+};
+
+export const buildProjectionCacheKey = (
+  sessionKey: string,
+  messages: ChatMessageEntry[],
+  showTextJustificationActivity: boolean,
+  showTurnChangedFiles: boolean,
+): string => {
+  const lastMessage = messages.length > 0 ? messages[messages.length - 1] : undefined;
+  const lastMessageId = lastMessage?.info?.id ?? '';
+  const lastMessagePartCount = lastMessage?.parts?.length ?? 0;
+  return [
+    sessionKey,
+    messages.length,
+    lastMessageId,
+    lastMessagePartCount,
+    buildMessagesVersionSignature(messages),
+    showTextJustificationActivity ? '1' : '0',
+    showTurnChangedFiles ? '1' : '0',
+  ].join('|');
+};
+
+export const getCachedProjection = (
+  sessionKey: string,
+  messages: ChatMessageEntry[],
+  showTextJustificationActivity: boolean,
+  showTurnChangedFiles: boolean,
+): TurnProjectionResult | undefined => {
+  const key = buildProjectionCacheKey(sessionKey, messages, showTextJustificationActivity, showTurnChangedFiles);
+  const cached = projectionCache.get(key);
+  if (cached) {
+    // LRU re-order: move hit to the end (most recent) so it survives
+    // eviction longer than entries that haven't been read recently.
+    projectionCache.delete(key);
+    projectionCache.set(key, cached);
+  }
+  return cached;
+};
+
+export const setCachedProjection = (
+  key: string,
+  projection: TurnProjectionResult,
+): void => {
+  projectionCache.delete(key);
+  const max = getProjectionCacheMax();
+  while (projectionCache.size >= max) {
+    const oldest = projectionCache.keys().next().value;
+    if (typeof oldest !== 'string') break;
+    projectionCache.delete(oldest);
+  }
+  projectionCache.set(key, projection);
+};
diff --git a/packages/ui/src/components/chat/markdown/decorate.ts b/packages/ui/src/components/chat/markdown/decorate.ts
index be50928d..2e8467e4 100644
--- a/packages/ui/src/components/chat/markdown/decorate.ts
+++ b/packages/ui/src/components/chat/markdown/decorate.ts
@@ -88,7 +88,11 @@ const decorateCodeBlocks = (root: HTMLElement, labels: DecorateLabels): void =>
     // Already wrapped (idempotent across morphdom passes).
     if (parent.closest('[data-component="markdown-code"]')) continue;
 
-    const language = pre.getAttribute('data-md-lang') ?? 'text';
+    // `data-md-lang` is stamped by the async highlight pass; on the synchronous
+    // first paint it isn't set yet, so fall back to the `language-*` class marked
+    // emits — keeps the card header label stable instead of flashing 'text'.
+    const classLang = pre.querySelector('code')?.className.match(/language-([\w+#.-]+)/)?.[1];
+    const language = pre.getAttribute('data-md-lang') ?? classLang ?? 'text';
 
     const wrapper = document.createElement('div');
     wrapper.setAttribute('data-component', 'markdown-code');
diff --git a/packages/ui/src/components/chat/markdown/markdownCore.ts b/packages/ui/src/components/chat/markdown/markdownCore.ts
index b1ec558c..4fc1ce19 100644
--- a/packages/ui/src/components/chat/markdown/markdownCore.ts
+++ b/packages/ui/src/components/chat/markdown/markdownCore.ts
@@ -306,16 +306,6 @@ const sanitize = (html: string): string => {
   return DOMPurify.sanitize(html, SANITIZE_CONFIG) as unknown as string;
 };
 
-const escapeHtml = (text: string): string =>
-  text
-    .replace(/&/g, '&amp;')
-    .replace(/</g, '&lt;')
-    .replace(/>/g, '&gt;')
-    .replace(/"/g, '&quot;')
-    .replace(/'/g, '&#39;');
-
-export const fallbackHtml = (markdown: string): string =>
-  escapeHtml(markdown).replace(/\r\n?/g, '\n').replace(/\n/g, '<br>');
 
 // ---------------------------------------------------------------------------
 // Per-block HTML cache (LRU, mirrors OpenCode's checksum cache)
@@ -349,6 +339,22 @@ const parseBlock = async (block: MarkdownBlock): Promise<string> => {
   return sanitize(highlighted);
 };
 
+/**
+ * Synchronous styled render for the first paint, before the async pipeline
+ * (Shiki-in-worker highlight) resolves. Produces the SAME structural HTML as
+ * `renderMarkdownBlocks` minus syntax coloring: paragraphs, lists, code blocks
+ * and bold all render at their final width, so the async pass only upgrades
+ * code-block colors — no flash of full-width raw markdown source. `parser.parse`
+ * is synchronous (marked is not configured `async`), so this never blocks on a
+ * worker round-trip.
+ */
+export const renderMarkdownSync = (text: string): string => {
+  if (!text) return '';
+  const parsed = parser.parse(text) as string;
+  const withMath = renderMathExpressions(parsed);
+  return sanitize(withMath);
+};
+
 export type RenderedBlock = {
   // Stable identity across renders for per-block DOM reconciliation. Encodes
   // content + mode + highlight so any change forces that block (and only that
diff --git a/packages/ui/src/components/chat/message/parts/ToolPart.tsx b/packages/ui/src/components/chat/message/parts/ToolPart.tsx
index e5fde9a1..b862860b 100644
--- a/packages/ui/src/components/chat/message/parts/ToolPart.tsx
+++ b/packages/ui/src/components/chat/message/parts/ToolPart.tsx
@@ -12,11 +12,7 @@ import { useOptionalThemeSystem } from '@/contexts/useThemeSystem';
 import { useEffectiveDirectory } from '@/hooks/useEffectiveDirectory';
 import { useSessionUIStore } from '@/sync/session-ui-store';
 import { useDirectorySync, useSessionMessageRecords, useEnsureSessionMessages } from '@/sync/sync-context';
-import { getSyncChildStores } from '@/sync/sync-refs';
 import { useUIStore } from '@/stores/useUIStore';
-import { useSessionActivity } from '@/hooks/useSessionActivity';
-import { opencodeClient } from '@/lib/opencode/client';
-import { isVSCodeRuntime } from '@/lib/desktop';
 import { sessionEvents } from '@/lib/sessionEvents';
 import { ScrollShadow } from '@/components/ui/ScrollShadow';
 import { Button } from '@/components/ui/button';
@@ -164,17 +160,6 @@ const normalizeToolName = (toolName: string | undefined | null): string => {
 };
 
 const MAX_DURATION_MS = 5 * 60 * 1000; // 5 minutes cap
-const TASK_TOOL_POLL_FAST_MS = 1200;
-const TASK_TOOL_POLL_IDLE_MS = 3200;
-const TASK_TOOL_POLL_HIDDEN_MS = 6000;
-const TASK_TOOL_INITIAL_FETCH_LIMIT = 500;
-const TASK_TOOL_ACTIVE_FETCH_LIMIT = 160;
-const TASK_TOOL_IDLE_FETCH_LIMIT = 80;
-const VSCODE_TASK_TOOL_INITIAL_FETCH_LIMIT = 30;
-const VSCODE_TASK_TOOL_ACTIVE_FETCH_LIMIT = 30;
-const VSCODE_TASK_TOOL_IDLE_FETCH_LIMIT = 30;
-const TASK_TOOL_NO_CHANGE_BACKOFF_AFTER_POLLS = 3;
-const TASK_TOOL_SETTLE_GRACE_MS = 2500;
 const TASK_TOOL_FALLBACK_RETRY_MS = 3000;
 const GIT_REFRESH_MUTATING_TOOLS = new Set([
     'bash',
@@ -1025,41 +1010,6 @@ const buildTaskSummaryEntriesFromSession = (messages: SessionMessageWithParts[])
     return entries;
 };
 
-const buildTaskSessionMessagesSignature = (messages: SessionMessageWithParts[]): string => {
-    if (!Array.isArray(messages) || messages.length === 0) {
-        return '0';
-    }
-
-    const lastMessage = messages[messages.length - 1];
-    const lastMessageId = typeof lastMessage?.info?.id === 'string' ? lastMessage.info.id : '';
-    const lastMessageUpdated =
-        typeof lastMessage?.info?.time?.completed === 'number'
-            ? lastMessage.info.time.completed
-            : typeof lastMessage?.info?.time?.created === 'number'
-                ? lastMessage.info.time.created
-                : 0;
-    const lastParts = Array.isArray(lastMessage?.parts) ? lastMessage.parts : [];
-    const lastPart = lastParts[lastParts.length - 1] as Record<string, unknown> | undefined;
-    const tailType = typeof lastPart?.type === 'string' ? lastPart.type : '';
-    const tailId = typeof lastPart?.id === 'string' ? lastPart.id : '';
-    const tailTextLength = (() => {
-        const textCandidate = lastPart?.text;
-        if (typeof textCandidate === 'string') {
-            return textCandidate.length;
-        }
-        const stateCandidate = lastPart?.state;
-        if (stateCandidate && typeof stateCandidate === 'object') {
-            const stateStatus = (stateCandidate as Record<string, unknown>).status;
-            if (typeof stateStatus === 'string') {
-                return stateStatus.length;
-            }
-        }
-        return 0;
-    })();
-
-    return `${messages.length}:${lastMessageId}:${lastMessageUpdated}:${lastParts.length}:${tailType}:${tailId}:${tailTextLength}`;
-};
-
 const getTaskSummaryLabel = (entry: TaskToolSummaryEntry): string => {
     const title = entry.state?.title;
     if (typeof title === 'string' && title.trim().length > 0) {
@@ -1117,6 +1067,144 @@ const shouldRenderGitPathLabel = (toolName: string, label: string): boolean => {
     return /^[A-Za-z0-9_-]+$/.test(baseName);
 };
 
+const getTaskSummaryEntryRenderSignature = (entry: TaskToolSummaryEntry): string => {
+    const toolName = normalizeToolName(entry.tool);
+    const status = entry.state?.status ?? '';
+    const label = getTaskSummaryLabel(entry);
+    return `${entry.id ?? ''}\u0001${toolName}\u0001${status}\u0001${label}`;
+};
+
+const areTaskSummaryEntriesRenderEqual = (
+    prevEntries: TaskToolSummaryEntry[],
+    nextEntries: TaskToolSummaryEntry[],
+): boolean => {
+    if (prevEntries === nextEntries) return true;
+    if (prevEntries.length !== nextEntries.length) return false;
+    for (let index = 0; index < prevEntries.length; index += 1) {
+        if (getTaskSummaryEntryRenderSignature(prevEntries[index]) !== getTaskSummaryEntryRenderSignature(nextEntries[index])) {
+            return false;
+        }
+    }
+    return true;
+};
+
+const TaskSummaryEntryRow = React.memo(({
+    entry,
+    isMobile,
+    animateTailText,
+    showToolFileIcons,
+}: {
+    entry: TaskToolSummaryEntry;
+    isMobile: boolean;
+    animateTailText: boolean;
+    showToolFileIcons: boolean;
+}) => {
+    const normalizedToolName = normalizeToolName(entry.tool);
+    const toolName = normalizedToolName.length > 0 ? normalizedToolName : 'tool';
+    const label = getTaskSummaryLabel(entry);
+    const hasLabel = label.trim().length > 0;
+    const status = entry.state?.status;
+    const displayName = getToolMetadata(toolName).displayName;
+
+    return (
+        <ToolRevealOnMount animate={animateTailText} wipe>
+            <div className={cn('flex gap-2 min-w-0 w-full', isMobile ? 'items-start' : 'items-center')}>
+                <span className="flex-shrink-0 text-foreground/80">{getToolIcon(toolName)}</span>
+                <span
+                    className="typography-meta text-foreground/80 flex-shrink-0"
+                    style={{ color: 'var(--tools-title)' }}
+                    title={displayName}
+                >
+                    {displayName}
+                </span>
+                {hasLabel ? (
+                    status !== 'error' && shouldRenderGitPathLabel(toolName, label) ? (
+                        renderAnimatedPathWithIcon(label, animateTailText, true, showToolFileIcons)
+                    ) : (
+                        status === 'error' ? (
+                            <span className={cn(
+                                'typography-meta flex-1 min-w-0 text-[var(--status-error)]',
+                                isMobile ? 'whitespace-normal break-words' : 'truncate',
+                            )}>
+                                {label}
+                            </span>
+                        ) : (
+                            <Text
+                                variant={animateTailText ? 'generate-effect' : 'static'}
+                                className={cn(
+                                    'typography-meta flex-1 min-w-0 text-muted-foreground/70',
+                                    isMobile ? 'whitespace-normal break-words' : 'truncate',
+                                )}
+                                style={{ color: 'var(--tools-description)' }}
+                                title={label}
+                            >
+                                {label}
+                            </Text>
+                        )
+                    )
+                ) : null}
+            </div>
+        </ToolRevealOnMount>
+    );
+}, (prev, next) => {
+    return prev.isMobile === next.isMobile
+        && prev.animateTailText === next.animateTailText
+        && prev.showToolFileIcons === next.showToolFileIcons
+        && getTaskSummaryEntryRenderSignature(prev.entry) === getTaskSummaryEntryRenderSignature(next.entry);
+});
+
+TaskSummaryEntryRow.displayName = 'TaskSummaryEntryRow';
+
+const TaskSummaryEntriesList = React.memo(({
+    entries,
+    isExpanded,
+    isMobile,
+    animateTailText,
+    showToolFileIcons,
+}: {
+    entries: TaskToolSummaryEntry[];
+    isExpanded: boolean;
+    isMobile: boolean;
+    animateTailText: boolean;
+    showToolFileIcons: boolean;
+}) => {
+    const visibleEntries = isExpanded ? entries : entries.slice(-6);
+    const hiddenCount = Math.max(0, entries.length - visibleEntries.length);
+    const visibleStartIndex = entries.length - visibleEntries.length;
+
+    return (
+        <ToolScrollableSection maxHeightClass={isExpanded ? 'max-h-[40vh]' : 'max-h-56'} disableHorizontal>
+            <div className="w-full min-w-0 space-y-1">
+                {hiddenCount > 0 ? (
+                    <div className="typography-micro text-muted-foreground/70">+{hiddenCount} more…</div>
+                ) : null}
+
+                {visibleEntries.map((entry, idx) => {
+                    const absoluteIndex = isExpanded ? idx : visibleStartIndex + idx;
+                    const rowKey = entry.id ?? `${getTaskSummaryEntryRenderSignature(entry)}:${absoluteIndex}`;
+                    return (
+                        <TaskSummaryEntryRow
+                            key={rowKey}
+                            entry={entry}
+                            isMobile={isMobile}
+                            animateTailText={animateTailText}
+                            showToolFileIcons={showToolFileIcons}
+                        />
+                    );
+                })}
+            </div>
+        </ToolScrollableSection>
+    );
+}, (prev, next) => {
+    return prev.isExpanded === next.isExpanded
+        && prev.isMobile === next.isMobile
+        && prev.animateTailText === next.animateTailText
+        && prev.showToolFileIcons === next.showToolFileIcons
+        && areTaskSummaryEntriesRenderEqual(prev.entries, next.entries);
+});
+
+TaskSummaryEntriesList.displayName = 'TaskSummaryEntriesList';
+
 const stripTaskMetadataFromOutput = (output: string): string => {
     // Strip only a trailing <task_metadata>...</task_metadata> block.
     return output.replace(/\n*<task_metadata>[\s\S]*?<\/task_metadata>\s*$/i, '').trimEnd();
@@ -1233,7 +1321,6 @@ const TaskToolSummary: React.FC<{
     const openContextPanelTab = useUIStore((state) => state.openContextPanelTab);
     const showToolFileIcons = useUIStore((state) => state.showToolFileIcons);
     const runtime = React.useContext(RuntimeAPIContext);
-    const displayEntries = entries;
 
     const trimmedOutput = typeof output === 'string'
         ? stripTaskMetadataFromOutput(output)
@@ -1262,7 +1349,7 @@ const TaskToolSummary: React.FC<{
         ? input.subagent_type
         : 'subagent';
 
-    if (displayEntries.length === 0 && !hasOutput && !sessionId) {
+    if (entries.length === 0 && !hasOutput && !sessionId) {
         return (
             <div className="relative pr-2 pb-2 pt-2 space-y-2 pl-[1.4375rem]">
                 <div className="typography-meta text-muted-foreground/70">
@@ -1272,9 +1359,6 @@ const TaskToolSummary: React.FC<{
         );
     }
 
-    const visibleEntries = isExpanded ? displayEntries : displayEntries.slice(-6);
-    const hiddenCount = Math.max(0, displayEntries.length - visibleEntries.length);
-
     return (
         <div
             className={cn(
@@ -1283,65 +1367,14 @@ const TaskToolSummary: React.FC<{
                 'before:top-[-0.25rem] before:bottom-0'
             )}
         >
-            {displayEntries.length > 0 ? (
-                <ToolScrollableSection maxHeightClass={isExpanded ? 'max-h-[40vh]' : 'max-h-56'} disableHorizontal>
-                    <div className="w-full min-w-0 space-y-1">
-                        {hiddenCount > 0 ? (
-                            <div className="typography-micro text-muted-foreground/70">+{hiddenCount} more…</div>
-                        ) : null}
-
-                        {visibleEntries.map((entry, idx) => {
-                            const normalizedToolName = normalizeToolName(entry.tool);
-                            const toolName = normalizedToolName.length > 0 ? normalizedToolName : 'tool';
-                            const label = getTaskSummaryLabel(entry);
-                            const hasLabel = label.trim().length > 0;
-                            const status = entry.state?.status;
-
-                            const displayName = getToolMetadata(toolName).displayName;
-
-                            return (
-                                <ToolRevealOnMount key={entry.id ?? `${toolName}-${idx}`} animate={animateTailText} wipe>
-                                    <div className={cn("flex gap-2 min-w-0 w-full", isMobile ? 'items-start' : 'items-center')}>
-                                        <span className="flex-shrink-0 text-foreground/80">{getToolIcon(toolName)}</span>
-                                        <span
-                                            className="typography-meta text-foreground/80 flex-shrink-0"
-                                            style={{ color: 'var(--tools-title)' }}
-                                            title={displayName}
-                                        >
-                                            {displayName}
-                                        </span>
-                                        {hasLabel ? (
-                                            status !== 'error' && shouldRenderGitPathLabel(toolName, label) ? (
-                                                renderAnimatedPathWithIcon(label, animateTailText, true, showToolFileIcons)
-                                            ) : (
-                                                status === 'error' ? (
-                                                    <span className={cn(
-                                                        'typography-meta flex-1 min-w-0 text-[var(--status-error)]',
-                                                        isMobile ? 'whitespace-normal break-words' : 'truncate'
-                                                    )}>
-                                                        {label}
-                                                    </span>
-                                                ) : (
-                                                    <Text
-                                                        variant={animateTailText ? 'generate-effect' : 'static'}
-                                                        className={cn(
-                                                            'typography-meta flex-1 min-w-0 text-muted-foreground/70',
-                                                            isMobile ? 'whitespace-normal break-words' : 'truncate'
-                                                        )}
-                                                        style={{ color: 'var(--tools-description)' }}
-                                                        title={label}
-                                                    >
-                                                        {label}
-                                                    </Text>
-                                                )
-                                            )
-                                        ) : null}
-                                    </div>
-                                </ToolRevealOnMount>
-                            );
-                        })}
-                    </div>
-                </ToolScrollableSection>
+            {entries.length > 0 ? (
+                <TaskSummaryEntriesList
+                    entries={entries}
+                    isExpanded={isExpanded}
+                    isMobile={isMobile}
+                    animateTailText={animateTailText}
+                    showToolFileIcons={showToolFileIcons}
+                />
             ) : null}
 
             {sessionId && (
@@ -1357,7 +1390,7 @@ const TaskToolSummary: React.FC<{
             )}
 
             {hasOutput ? (
-                <div className={cn('space-y-1', (displayEntries.length > 0 || sessionId) && 'pt-1')}
+                <div className={cn('space-y-1', (entries.length > 0 || sessionId) && 'pt-1')}
                 >
                     <button
                         type="button"
@@ -2147,12 +2180,11 @@ const ToolPartContent: React.FC<ToolPartProps> = ({
                 isTaskTool,
                 parentSessionId: currentSessionId ?? undefined,
                 taskStartTime: taskSessionResolutionStart,
-                isTaskFinalized: isFinalized,
                 sessions: storeState.session,
                 sessionStatusMap: storeState.session_status,
                 hasRetried: taskFallbackRetried,
             });
-        }, [explicitTaskSessionId, isTaskTool, currentSessionId, taskSessionResolutionStart, isFinalized, taskFallbackRetried]),
+        }, [explicitTaskSessionId, isTaskTool, currentSessionId, taskSessionResolutionStart, taskFallbackRetried]),
         currentDirectory,
     );
 
@@ -2172,49 +2204,7 @@ const ToolPartContent: React.FC<ToolPartProps> = ({
         return buildTaskSummaryEntriesFromSession(childSessionMessages);
     }, [childSessionMessages, isTaskTool, taskSessionId]);
 
-    const childSessionHasInFlightTools = React.useMemo(() => {
-        if (!isTaskTool || !taskSessionId || !Array.isArray(childSessionMessages) || childSessionMessages.length === 0) {
-            return false;
-        }
-
-        for (const message of childSessionMessages) {
-            if (message?.info?.role !== 'assistant') {
-                continue;
-            }
-            const parts = Array.isArray(message.parts) ? message.parts : [];
-            for (const childPart of parts) {
-                if (childPart?.type !== 'tool') {
-                    continue;
-                }
-                const childStatus =
-                    typeof childPart === 'object' && childPart !== null && 'state' in childPart
-                        ? (childPart.state as { status?: string } | undefined)?.status
-                        : undefined;
-                if (childStatus === 'running' || childStatus === 'pending' || childStatus === 'started') {
-                    return true;
-                }
-            }
-        }
-
-        return false;
-    }, [childSessionMessages, isTaskTool, taskSessionId]);
-
-    const childSessionActivity = useSessionActivity(taskSessionId, currentDirectory);
-    const [taskChildSeenActive, setTaskChildSeenActive] = React.useState(false);
-    const [taskChildPollingStopped, setTaskChildPollingStopped] = React.useState(false);
-    const [taskPendingFinalFetch, setTaskPendingFinalFetch] = React.useState(false);
-
-    const taskPollNoChangeCountRef = React.useRef(0);
-    const taskPollLastSignatureRef = React.useRef<string>('');
-    const taskFinalFetchDoneRef = React.useRef(false);
-
     React.useEffect(() => {
-        setTaskChildSeenActive(false);
-        setTaskChildPollingStopped(false);
-        setTaskPendingFinalFetch(false);
-        taskPollNoChangeCountRef.current = 0;
-        taskPollLastSignatureRef.current = '';
-        taskFinalFetchDoneRef.current = false;
         setTaskFallbackRetried(false);
     }, [taskSessionId]);
 
@@ -2251,148 +2241,6 @@ const ToolPartContent: React.FC<ToolPartProps> = ({
         taskSessionResolutionStart,
     ]);
 
-    React.useEffect(() => {
-        if (hasFinalMetadataTaskSummary || !isTaskTool || !taskSessionId) {
-            return;
-        }
-
-        const childSessionIsActive =
-            childSessionActivity.phase === 'busy'
-            || childSessionActivity.phase === 'retry'
-            || childSessionHasInFlightTools;
-
-        if (childSessionIsActive) {
-            if (!taskChildSeenActive) {
-                setTaskChildSeenActive(true);
-            }
-            if (taskChildPollingStopped) {
-                setTaskChildPollingStopped(false);
-            }
-            if (taskPendingFinalFetch) {
-                setTaskPendingFinalFetch(false);
-            }
-            return;
-        }
-
-        // Always stop polling if already done.
-        if (taskChildPollingStopped && taskFinalFetchDoneRef.current) {
-            return;
-        }
-
-        // Normal settle path: child went idle after we saw it active, and we have entries.
-        // Schedule a grace period before marking polling as stopped.
-        if (taskChildSeenActive && childSessionTaskSummaryEntries.length > 0 && !taskChildPollingStopped) {
-            if (typeof window === 'undefined') {
-                setTaskChildPollingStopped(true);
-                return;
-            }
-
-            const timer = window.setTimeout(() => {
-                setTaskChildPollingStopped(true);
-            }, TASK_TOOL_SETTLE_GRACE_MS);
-
-            return () => {
-                window.clearTimeout(timer);
-            };
-        }
-
-        // Final-fetch path: child went idle before parent saw it active, or we have no
-        // entries yet. First stop polling after the settle grace period. A separate
-        // effect performs the final fetch once polling has fully stopped, avoiding
-        // races with any in-flight polling response.
-        if (!taskChildPollingStopped && !taskFinalFetchDoneRef.current) {
-            if (typeof window === 'undefined') {
-                setTaskPendingFinalFetch(true);
-                setTaskChildPollingStopped(true);
-                return;
-            }
-
-            const timer = window.setTimeout(() => {
-                setTaskPendingFinalFetch(true);
-                setTaskChildPollingStopped(true);
-            }, TASK_TOOL_SETTLE_GRACE_MS);
-
-            return () => {
-                window.clearTimeout(timer);
-            };
-        }
-    }, [
-        childSessionActivity.phase,
-        childSessionHasInFlightTools,
-        childSessionTaskSummaryEntries.length,
-        currentDirectory,
-        hasFinalMetadataTaskSummary,
-        activeLatched,
-        isFinalized,
-        isTaskTool,
-        taskPendingFinalFetch,
-        taskChildPollingStopped,
-        taskChildSeenActive,
-        taskSessionId,
-    ]);
-
-    React.useEffect(() => {
-        if (hasFinalMetadataTaskSummary || !isTaskTool || !taskSessionId || !taskChildPollingStopped || !taskPendingFinalFetch || taskFinalFetchDoneRef.current) {
-            return;
-        }
-
-        let cancelled = false;
-        const capturedSessionId = taskSessionId;
-
-        const runFinalFetch = async () => {
-            try {
-                const scopedClient = opencodeClient.getScopedSdkClient(currentDirectory);
-                const response = await scopedClient.session.messages({
-                    sessionID: capturedSessionId,
-                    limit: isVSCodeRuntime() ? VSCODE_TASK_TOOL_INITIAL_FETCH_LIMIT : TASK_TOOL_INITIAL_FETCH_LIMIT,
-                });
-
-                if (cancelled) {
-                    return;
-                }
-
-                const messages = response.data ?? [];
-                if (Array.isArray(messages) && messages.length > 0) {
-                    const childStores = getSyncChildStores();
-                    childStores.update(currentDirectory, (prev) => {
-                        const records = messages as SessionMessageWithParts[];
-                        const partPatch: Record<string, import('@opencode-ai/sdk/v2').Part[]> = { ...prev.part };
-                        for (const rec of records) {
-                            partPatch[rec.info.id] = rec.parts;
-                        }
-                        return {
-                            message: { ...prev.message, [capturedSessionId]: records.map((r) => r.info) as import('@opencode-ai/sdk/v2').Message[] },
-                            part: partPatch,
-                        };
-                    });
-                }
-
-                taskFinalFetchDoneRef.current = true;
-                setTaskPendingFinalFetch(false);
-            } catch {
-                if (cancelled) {
-                    return;
-                }
-
-                setTaskPendingFinalFetch(false);
-                setTaskChildPollingStopped(false);
-            }
-        };
-
-        void runFinalFetch();
-
-        return () => {
-            cancelled = true;
-        };
-    }, [
-        currentDirectory,
-        hasFinalMetadataTaskSummary,
-        isTaskTool,
-        taskChildPollingStopped,
-        taskPendingFinalFetch,
-        taskSessionId,
-    ]);
-
     React.useEffect(() => {
         if (typeof time?.end === 'number' || typeof pinnedTime.end === 'number') {
             setLocalFinalizedAt(undefined);
@@ -2425,147 +2273,25 @@ const ToolPartContent: React.FC<ToolPartProps> = ({
         }
         return metadataTaskSummaryEntries;
     }, [childSessionTaskSummaryEntries, metadataTaskSummaryEntries]);
+    const taskSummaryRenderSignature = React.useMemo(() => {
+        return taskSummaryEntries.map(getTaskSummaryEntryRenderSignature).join('\u0000');
+    }, [taskSummaryEntries]);
+    const lastTaskSummaryRenderSignatureRef = React.useRef<string | null>(null);
 
-    React.useEffect(() => {
-        if (!isTaskTool || !taskSessionId) {
-            return;
-        }
-
-        const childSessionActive = childSessionActivity.phase === 'busy' || childSessionActivity.phase === 'retry';
-        if (hasFinalMetadataTaskSummary) {
-            return;
-        }
-
-        const shouldPoll =
-            !taskChildPollingStopped
-            && (childSessionHasInFlightTools || childSessionActive || childSessionTaskSummaryEntries.length === 0);
-        const shouldFetchSnapshot = !taskPendingFinalFetch && (childSessionTaskSummaryEntries.length === 0 || shouldPoll);
-        if (!shouldFetchSnapshot) {
-            return;
-        }
-
-        let cancelled = false;
-        let pollTimer: number | undefined;
-
-        const isVisible = () => {
-            if (typeof document === 'undefined') {
-                return true;
-            }
-            return document.visibilityState === 'visible';
-        };
-
-        const resolveFetchLimit = (isInitialFetch: boolean) => {
-            if (isVSCodeRuntime()) {
-                if (isInitialFetch && childSessionTaskSummaryEntries.length === 0) {
-                    return VSCODE_TASK_TOOL_INITIAL_FETCH_LIMIT;
-                }
-                if (isActive || childSessionHasInFlightTools || childSessionActive) {
-                    return VSCODE_TASK_TOOL_ACTIVE_FETCH_LIMIT;
-                }
-                return VSCODE_TASK_TOOL_IDLE_FETCH_LIMIT;
-            }
-
-            if (isInitialFetch && childSessionTaskSummaryEntries.length === 0) {
-                return TASK_TOOL_INITIAL_FETCH_LIMIT;
-            }
-            if (isActive || childSessionHasInFlightTools || childSessionActive) {
-                return TASK_TOOL_ACTIVE_FETCH_LIMIT;
-            }
-            return TASK_TOOL_IDLE_FETCH_LIMIT;
-        };
-
-        const resolvePollDelay = () => {
-            if (!isVisible()) {
-                return TASK_TOOL_POLL_HIDDEN_MS;
-            }
-            if (taskPollNoChangeCountRef.current >= TASK_TOOL_NO_CHANGE_BACKOFF_AFTER_POLLS) {
-                return TASK_TOOL_POLL_IDLE_MS;
-            }
-            return TASK_TOOL_POLL_FAST_MS;
-        };
-
-        const scheduleNextPoll = () => {
-            if (!shouldPoll || typeof window === 'undefined' || cancelled) {
-                return;
-            }
-            pollTimer = window.setTimeout(() => {
-                pollTimer = undefined;
-                void fetchSessionMessages(false);
-            }, resolvePollDelay());
-        };
-
-        const fetchSessionMessages = async (isInitialFetch: boolean) => {
-            try {
-                const scopedClient = opencodeClient.getScopedSdkClient(currentDirectory);
-                const response = await scopedClient.session.messages({
-                    sessionID: taskSessionId,
-                    limit: resolveFetchLimit(isInitialFetch),
-                });
-                const messages = response.data ?? [];
-                if (cancelled || !Array.isArray(messages) || messages.length === 0) {
-                    return;
-                }
-
-                const nextSignature = buildTaskSessionMessagesSignature(messages as SessionMessageWithParts[]);
-                if (nextSignature === taskPollLastSignatureRef.current) {
-                    taskPollNoChangeCountRef.current += 1;
-                    return;
-                }
-
-                taskPollLastSignatureRef.current = nextSignature;
-                taskPollNoChangeCountRef.current = 0;
-                // Inject fetched subagent messages into sync child store
-                const childStores = getSyncChildStores();
-                childStores.update(currentDirectory, (prev) => {
-                    const records = messages as SessionMessageWithParts[];
-                    const partPatch: Record<string, import('@opencode-ai/sdk/v2').Part[]> = { ...prev.part };
-                    for (const rec of records) {
-                        partPatch[rec.info.id] = rec.parts;
-                    }
-                    return {
-                        message: { ...prev.message, [taskSessionId]: records.map((r) => r.info) as import('@opencode-ai/sdk/v2').Message[] },
-                        part: partPatch,
-                    };
-                });
-            } catch {
-                // Ignore transient subagent fetch errors.
-            } finally {
-                scheduleNextPoll();
-            }
-        };
-
-        void fetchSessionMessages(true);
-
-        return () => {
-            cancelled = true;
-            if (typeof pollTimer === 'number') {
-                window.clearTimeout(pollTimer);
-            }
-        };
-    }, [
-        childSessionActivity.phase,
-        childSessionHasInFlightTools,
-        childSessionTaskSummaryEntries.length,
-        currentDirectory,
-        hasFinalMetadataTaskSummary,
-        isActive,
-        isTaskTool,
-        taskPendingFinalFetch,
-        taskChildPollingStopped,
-        taskSessionId,
-    ]);
-
-    const taskSummaryLenRef = React.useRef<number>(taskSummaryEntries.length);
     React.useEffect(() => {
         if (!isTaskTool) {
+            lastTaskSummaryRenderSignatureRef.current = null;
             return;
         }
-        if (taskSummaryLenRef.current === taskSummaryEntries.length) {
+
+        const previous = lastTaskSummaryRenderSignatureRef.current;
+        lastTaskSummaryRenderSignatureRef.current = taskSummaryRenderSignature;
+        if (previous === null || previous === taskSummaryRenderSignature || taskSummaryEntries.length === 0) {
             return;
         }
-        taskSummaryLenRef.current = taskSummaryEntries.length;
-        onContentChange?.('structural');
-    }, [isTaskTool, onContentChange, taskSummaryEntries.length]);
+
+        onContentChangeRef.current?.('structural');
+    }, [isTaskTool, taskSummaryEntries.length, taskSummaryRenderSignature]);
 
     const diffStats = React.useMemo(() => {
         return (normalizedPartTool === 'edit' || normalizedPartTool === 'multiedit' || normalizedPartTool === 'apply_patch')
diff --git a/packages/ui/src/components/chat/message/parts/__tests__/resolveFallbackTaskSessionId.test.js b/packages/ui/src/components/chat/message/parts/__tests__/resolveFallbackTaskSessionId.test.js
index 40943064..947e6315 100644
--- a/packages/ui/src/components/chat/message/parts/__tests__/resolveFallbackTaskSessionId.test.js
+++ b/packages/ui/src/components/chat/message/parts/__tests__/resolveFallbackTaskSessionId.test.js
@@ -31,13 +31,16 @@ describe('resolveFallbackTaskSessionId', () => {
     expect(result).toBeUndefined();
   });
 
-  it('returns undefined when task is finalized', () => {
+  it('returns undefined when multiple idle candidates are ambiguous', () => {
     const result = resolveFallbackTaskSessionId({
       isTaskTool: true,
       parentSessionId,
       taskStartTime,
-      sessions: [],
-      isTaskFinalized: true,
+      sessions: [
+        makeSession({ id: 'child-a', parentID: parentSessionId, time: { created: taskStartTime + 100 } }),
+        makeSession({ id: 'child-b', parentID: parentSessionId, time: { created: taskStartTime + 200 } }),
+      ],
+      sessionStatusMap: {},
     });
     expect(result).toBeUndefined();
   });
diff --git a/packages/ui/src/components/chat/message/parts/resolveFallbackTaskSessionId.ts b/packages/ui/src/components/chat/message/parts/resolveFallbackTaskSessionId.ts
index 897747ad..dc685a0f 100644
--- a/packages/ui/src/components/chat/message/parts/resolveFallbackTaskSessionId.ts
+++ b/packages/ui/src/components/chat/message/parts/resolveFallbackTaskSessionId.ts
@@ -29,8 +29,6 @@ export interface ResolveFallbackParams {
   parentSessionId: string | undefined;
   /** When the task tool started (ms timestamp) */
   taskStartTime: number | undefined;
-  /** True when the task tool is finalized (completed/error/etc.) */
-  isTaskFinalized?: boolean;
   /** Sessions from the directory store */
   sessions: Session[];
   /** Session status map from the sync store */
@@ -45,8 +43,8 @@ export interface ResolveFallbackParams {
  *
  * Returns `undefined` when:
  * - Not a task tool
- * - Task is finalized
  * - Parent session is unknown
+ * - Task start time is unknown
  * - No unambiguous match found
  */
 export function resolveFallbackTaskSessionId(params: ResolveFallbackParams): string | undefined {
@@ -54,7 +52,6 @@ export function resolveFallbackTaskSessionId(params: ResolveFallbackParams): str
     isTaskTool,
     parentSessionId,
     taskStartTime,
-    isTaskFinalized = false,
     sessions,
     sessionStatusMap,
     hasRetried = false,
@@ -64,6 +61,10 @@ export function resolveFallbackTaskSessionId(params: ResolveFallbackParams): str
     return undefined;
   }
 
+  if (typeof taskStartTime !== 'number') {
+    return undefined;
+  }
+
   // Filter candidate sessions: parentID matches the current session.
   let candidates = sessions.filter((session) => {
     if (!session?.id || session.parentID !== parentSessionId) {
@@ -72,19 +73,14 @@ export function resolveFallbackTaskSessionId(params: ResolveFallbackParams): str
     return true;
   });
 
-  // When the task is still running, apply no time window — late-appearing
-  // child sessions should still match. Once finalized, restrict to sessions
-  // created within a generous window around the task start to avoid binding
-  // to stale siblings. If taskStartTime is unavailable (cross-OpenCode
-  // sessions), skip the time filter entirely.
-  if (typeof taskStartTime === 'number' && isTaskFinalized) {
-    const windowMs = hasRetried ? TASK_SESSION_MATCH_WINDOW_WIDE_MS : TASK_SESSION_MATCH_WINDOW_MS;
-    const latestAllowed = taskStartTime + windowMs;
-    candidates = candidates.filter((session) => {
-      const created = session.time?.created;
-      return typeof created === 'number' && created >= taskStartTime - 2_000 && created <= latestAllowed;
-    });
-  }
+  // Apply the time window even while running. Without it, a newly rendered task
+  // can briefly bind to the previous child session before its own child exists.
+  const windowMs = hasRetried ? TASK_SESSION_MATCH_WINDOW_WIDE_MS : TASK_SESSION_MATCH_WINDOW_MS;
+  const latestAllowed = taskStartTime + windowMs;
+  candidates = candidates.filter((session) => {
+    const created = session.time?.created;
+    return typeof created === 'number' && created >= taskStartTime && created <= latestAllowed;
+  });
 
   if (candidates.length === 0) {
     return undefined;
@@ -105,18 +101,6 @@ export function resolveFallbackTaskSessionId(params: ResolveFallbackParams): str
     return liveCandidates[0].id;
   }
 
-  // All idle: pick the most recently created child session.
-  // This handles the common case where a delegation completed and the
-  // user is viewing the task tool result inline.
-  if (liveCandidates.length === 0 && candidates.length > 1) {
-    const sorted = [...candidates].sort((a, b) => {
-      const aCreated = typeof a.time?.created === 'number' ? a.time.created : 0;
-      const bCreated = typeof b.time?.created === 'number' ? b.time.created : 0;
-      return bCreated - aCreated;
-    });
-    return sorted[0].id;
-  }
-
   // Ambiguous — do not guess
   return undefined;
 }
diff --git a/packages/ui/src/components/chat/revertedMessageDockState.test.ts b/packages/ui/src/components/chat/revertedMessageDockState.test.ts
new file mode 100644
index 00000000..22d9e8c8
--- /dev/null
+++ b/packages/ui/src/components/chat/revertedMessageDockState.test.ts
@@ -0,0 +1,89 @@
+import { describe, expect, test } from 'bun:test';
+import type { Message, Part } from '@opencode-ai/sdk/v2/client';
+import type { State } from '@/sync/types';
+
+import { EMPTY_REVERTED_MESSAGE_DOCK_STATE, buildRevertedMessageDockState } from './revertedMessageDockState';
+
+const message = (id: string, role: 'user' | 'assistant'): Message => ({
+    id,
+    role,
+    sessionID: 'ses_1',
+    time: { created: 1 },
+} as Message);
+
+const textPart = (id: string, text: string): Part => ({
+    id,
+    type: 'text',
+    text,
+} as Part);
+
+const state = (partial: Partial<State>): Pick<State, 'session' | 'message' | 'part'> => ({
+    session: [],
+    message: {},
+    part: {},
+    ...partial,
+});
+
+describe('buildRevertedMessageDockState', () => {
+    test('returns a shared empty state when the session is not reverted', () => {
+        const first = buildRevertedMessageDockState(state({}), 'ses_1');
+        const second = buildRevertedMessageDockState(
+            state({ part: { assistant_1: [textPart('part_1', 'streaming')] } }),
+            'ses_1',
+            first,
+        );
+
+        expect(first).toBe(EMPTY_REVERTED_MESSAGE_DOCK_STATE);
+        expect(second).toBe(EMPTY_REVERTED_MESSAGE_DOCK_STATE);
+    });
+
+    test('reuses the previous state when unrelated assistant parts change', () => {
+        const user = message('user_1', 'user');
+        const userParts = [textPart('part_user', 'hello')];
+        const first = buildRevertedMessageDockState(
+            state({
+                session: [{ id: 'ses_1', revert: { messageID: 'user_1' } } as State['session'][number]],
+                message: { ses_1: [user, message('assistant_1', 'assistant')] },
+                part: { user_1: userParts, assistant_1: [textPart('part_a', 'a')] },
+            }),
+            'ses_1',
+        );
+
+        const second = buildRevertedMessageDockState(
+            state({
+                session: [{ id: 'ses_1', revert: { messageID: 'user_1' } } as State['session'][number]],
+                message: { ses_1: [user, message('assistant_1', 'assistant')] },
+                part: { user_1: userParts, assistant_1: [textPart('part_a2', 'updated')] },
+            }),
+            'ses_1',
+            first,
+        );
+
+        expect(second).toBe(first);
+    });
+
+    test('updates when a reverted user message part changes', () => {
+        const user = message('user_1', 'user');
+        const first = buildRevertedMessageDockState(
+            state({
+                session: [{ id: 'ses_1', revert: { messageID: 'user_1' } } as State['session'][number]],
+                message: { ses_1: [user] },
+                part: { user_1: [textPart('part_user', 'hello')] },
+            }),
+            'ses_1',
+        );
+
+        const second = buildRevertedMessageDockState(
+            state({
+                session: [{ id: 'ses_1', revert: { messageID: 'user_1' } } as State['session'][number]],
+                message: { ses_1: [user] },
+                part: { user_1: [textPart('part_user_updated', 'updated')] },
+            }),
+            'ses_1',
+            first,
+        );
+
+        expect(second).not.toBe(first);
+        expect(second.records).toHaveLength(1);
+    });
+});
diff --git a/packages/ui/src/components/chat/revertedMessageDockState.ts b/packages/ui/src/components/chat/revertedMessageDockState.ts
new file mode 100644
index 00000000..4ae3b017
--- /dev/null
+++ b/packages/ui/src/components/chat/revertedMessageDockState.ts
@@ -0,0 +1,73 @@
+import type { Message, Part } from '@opencode-ai/sdk/v2/client';
+import type { State } from '@/sync/types';
+
+export type RevertedMessageRecord = {
+    message: Message & { role: 'user' };
+    parts: Part[];
+};
+
+export type RevertedMessageDockState = {
+    revertMessageID?: string;
+    records: RevertedMessageRecord[];
+};
+
+const EMPTY_PARTS: Part[] = [];
+const EMPTY_REVERTED_RECORDS: RevertedMessageRecord[] = [];
+
+export const EMPTY_REVERTED_MESSAGE_DOCK_STATE: RevertedMessageDockState = {
+    revertMessageID: undefined,
+    records: EMPTY_REVERTED_RECORDS,
+};
+
+const isUserMessage = (message: Message): message is Message & { role: 'user' } => {
+    return message.role === 'user';
+};
+
+const areRecordsEqual = (left: RevertedMessageRecord[], right: RevertedMessageRecord[]): boolean => {
+    if (left === right) return true;
+    if (left.length !== right.length) return false;
+    for (let index = 0; index < left.length; index += 1) {
+        if (left[index]?.message !== right[index]?.message || left[index]?.parts !== right[index]?.parts) {
+            return false;
+        }
+    }
+    return true;
+};
+
+export const buildRevertedMessageDockState = (
+    state: Pick<State, 'session' | 'message' | 'part'>,
+    sessionId: string | null,
+    previous: RevertedMessageDockState = EMPTY_REVERTED_MESSAGE_DOCK_STATE,
+): RevertedMessageDockState => {
+    if (!sessionId) {
+        return EMPTY_REVERTED_MESSAGE_DOCK_STATE;
+    }
+
+    const session = state.session.find((item) => item.id === sessionId);
+    const revertMessageID = (session as { revert?: { messageID?: string } } | undefined)?.revert?.messageID;
+    if (!revertMessageID) {
+        return EMPTY_REVERTED_MESSAGE_DOCK_STATE;
+    }
+
+    const messages = state.message[sessionId] ?? [];
+    const records: RevertedMessageRecord[] = [];
+    for (const message of messages) {
+        if (!isUserMessage(message) || message.id < revertMessageID) {
+            continue;
+        }
+        records.push({
+            message,
+            parts: state.part[message.id] ?? EMPTY_PARTS,
+        });
+    }
+
+    const next = records.length === 0 ? EMPTY_REVERTED_RECORDS : records;
+    if (previous.revertMessageID === revertMessageID && areRecordsEqual(previous.records, next)) {
+        return previous;
+    }
+
+    return {
+        revertMessageID,
+        records: next,
+    };
+};
diff --git a/packages/ui/src/components/session/SessionFolderItem.tsx b/packages/ui/src/components/session/SessionFolderItem.tsx
index 27c569d0..953a3b23 100644
--- a/packages/ui/src/components/session/SessionFolderItem.tsx
+++ b/packages/ui/src/components/session/SessionFolderItem.tsx
@@ -3,6 +3,7 @@ import { cn } from '@/lib/utils';
 import type { SessionFolder } from '@/stores/useSessionFoldersStore';
 import { useI18n } from '@/lib/i18n';
 import { Icon } from "@/components/icon/Icon";
+import type { SessionNodeChildRenderExtras, SessionNodeRenderExtras } from './sidebar/sessionNodeItemUtils';
 
 interface SessionFolderItemProps<TSessionNode> {
   folder: SessionFolder;
@@ -19,7 +20,17 @@ interface SessionFolderItemProps<TSessionNode> {
     groupDir?: string | null,
     projectId?: string | null,
     archivedBucket?: boolean,
+    secondaryMeta?: { projectLabel?: string | null; branchLabel?: string | null } | null,
+    renderContext?: 'project' | 'recent',
+    renderExtras?: SessionNodeChildRenderExtras,
   ) => React.ReactNode;
+  /**
+   * Returns the precomputed per-row render extras for a given node. The
+   * group precomputes subtree-contains lookups once, then resolves a
+   * per-node structure key here so SessionNodeItem's React.memo comparator
+   * can answer with a single string compare instead of a recursive walk.
+   */
+  getRenderExtras?: (node: TSessionNode) => SessionNodeRenderExtras<TSessionNode> | undefined;
   groupDirectory?: string | null;
   projectId?: string | null;
   mobileVariant?: boolean;
@@ -54,6 +65,7 @@ const SessionFolderItemBase = <TSessionNode,>({
   onRename,
   onDelete,
   renderSessionNode,
+  getRenderExtras,
   groupDirectory,
   projectId,
   mobileVariant = false,
@@ -320,7 +332,7 @@ const SessionFolderItemBase = <TSessionNode,>({
           {/* Then sessions */}
           {sessions.length > 0 ? (
             sessions.map((node) =>
-              renderSessionNode(node, 0, groupDirectory ?? null, projectId ?? null, archivedBucket),
+              renderSessionNode(node, 0, groupDirectory ?? null, projectId ?? null, archivedBucket, undefined, 'project', getRenderExtras?.(node)),
             )
           ) : !subFolderItems ? (
             <div className="py-1 pl-1.5 text-left typography-micro text-muted-foreground/70">
diff --git a/packages/ui/src/components/session/SessionSidebar.tsx b/packages/ui/src/components/session/SessionSidebar.tsx
index 69cce2ec..8b4edaf3 100644
--- a/packages/ui/src/components/session/SessionSidebar.tsx
+++ b/packages/ui/src/components/session/SessionSidebar.tsx
@@ -41,9 +41,11 @@ import { SidebarActivitySections } from './sidebar/SidebarActivitySections';
 import { SidebarFooter } from './sidebar/SidebarFooter';
 import { SidebarProjectsList } from './sidebar/SidebarProjectsList';
 import { SessionNodeItem } from './sidebar/SessionNodeItem';
+import type { SessionNodeRenderExtras } from './sidebar/sessionNodeItemUtils';
 import { useUpdateStore } from '@/stores/useUpdateStore';
 import { useShallow } from 'zustand/react/shallow';
 import { listProjectWorktrees } from '@/lib/worktrees/worktreeManager';
+import { checkIsGitRepository } from '@/lib/gitApi';
 import type { WorktreeMetadata } from '@/types/worktree';
 import type { SortableDragHandleProps } from './sidebar/sortableItems';
 import {
@@ -55,7 +57,7 @@ import {
   type DeleteSessionConfirmState,
 } from './sidebar/ConfirmDialogs';
 import { BulkActionBar } from './sidebar/BulkActionBar';
-import { useSessionMultiSelectStore } from '@/stores/useSessionMultiSelectStore';
+import { useSidebarBulkActions } from './sidebar/hooks/useSidebarBulkActions';
 import { useSessionDisplayStore } from '@/stores/useSessionDisplayStore';
 import { type SessionGroup, type SessionNode } from './sidebar/types';
 import {
@@ -153,6 +155,14 @@ const isKnownActiveSessionDirectory = (
 
 const SIDEBAR_PR_NO_PR_RETRY_MS = 5 * 60_000;
 
+const EMPTY_SUBTREE_SET: Set<string> = new Set();
+
+const useStableRenderCallback = <Args extends unknown[], Return>(handler: (...args: Args) => Return): ((...args: Args) => Return) => {
+  const handlerRef = React.useRef(handler);
+  handlerRef.current = handler;
+  return React.useCallback((...args: Args) => handlerRef.current(...args), []);
+};
+
 interface SessionSidebarProps {
   mobileVariant?: boolean;
   onSessionSelected?: (sessionId: string) => void;
@@ -383,6 +393,16 @@ export const SessionSidebar: React.FC<SessionSidebarProps> = ({
     syncSessionsSnapshotRef.current = liveSessions;
   }, [syncSessionStructureSignature, liveSessions]);
 
+  // Batched live-session index. Building this here turns the per-row
+  // `useSession(session.id)` reads in SessionNodeItem (each of which
+  // iterates all child-stores via `findLiveSession`) into a single
+  // Map lookup. With M visible rows, that changes an O(M × child-stores)
+  // work to O(child-stores) once per Sidebar render.
+  const liveSessionById = React.useMemo(
+    () => new Map(liveSessions.map((session) => [session.id, session] as const)),
+    [liveSessions],
+  );
+
   const projectWorktreeDiscoveryKey = React.useMemo(
     () => projects
       .map((project) => `${project.id}:${normalizePath(project.path) ?? ''}`)
@@ -399,6 +419,10 @@ export const SessionSidebar: React.FC<SessionSidebarProps> = ({
     void refreshGlobalSessions(syncSessionsSnapshotRef.current);
   }, []);
 
+  // Tracks the last project list we already kicked off discovery for.
+  // A re-mount with the same project set shouldn't fan out another
+  // burst of `checkIsGitRepository` / `listProjectWorktrees` calls.
+  const discoveredProjectsRef = React.useRef<string>('');
   React.useEffect(() => {
     let cancelled = false;
 
@@ -409,24 +433,39 @@ export const SessionSidebar: React.FC<SessionSidebarProps> = ({
       const worktreesByProject = new Map<string, WorktreeMetadata[]>();
       const allWorktrees: WorktreeMetadata[] = [];
 
-      await Promise.all(
-        projectEntries.map(async (project) => {
+      // Constrain fanout: previously `Promise.all(projects.map(...))` could
+      // spawn dozens of concurrent `git worktree list` and
+      // `checkIsGitRepository` calls on cold start, each touching the
+      // worktree process. Concurrency=3 keeps startup latency low while
+      // bounding peak worktree-process load.
+      const worktreeConcurrency = 3;
+      let cursor = 0;
+      const workers = Array.from({ length: worktreeConcurrency }, async () => {
+        while (true) {
+          const nextIndex = cursor;
+          cursor += 1;
+          if (nextIndex >= projectEntries.length) return;
+          const project = projectEntries[nextIndex];
           const projectPath = normalizePath(project.path);
-          if (!projectPath) return;
+          if (!projectPath) continue;
           try {
-            // Use store-cached isGitRepo when available; fall back to direct check for initial worktree discovery
+            // Use store-cached isGitRepo when available; fall back to
+            // a direct check for projects the Git store hasn't seen yet.
+            // Forcing `ensureStatus` here also warms the store so the
+            // PR/render paths downstream can read isGitRepo for free.
             const cachedIsGitRepo = useGitStore.getState().directories.get(projectPath)?.isGitRepo;
-            const isGitRepo = cachedIsGitRepo ?? await import('@/lib/gitApi').then(m => m.checkIsGitRepository(projectPath));
-            if (!isGitRepo) return;
+            const isGitRepo = cachedIsGitRepo ?? await checkIsGitRepository(projectPath);
+            if (!isGitRepo) continue;
             const worktrees = await listProjectWorktrees({ id: project.id, path: projectPath });
-            if (cancelled || worktrees.length === 0) return;
+            if (cancelled || worktrees.length === 0) continue;
             worktreesByProject.set(projectPath, worktrees);
             allWorktrees.push(...worktrees);
           } catch {
             // ignore discovery errors
           }
-        }),
-      );
+        }
+      });
+      await Promise.all(workers);
 
       if (cancelled) return;
 
@@ -436,6 +475,11 @@ export const SessionSidebar: React.FC<SessionSidebarProps> = ({
       });
     };
 
+    // Skip if we already discovered worktrees for this exact project set.
+    if (discoveredProjectsRef.current === projectWorktreeDiscoveryKey) {
+      return;
+    }
+    discoveredProjectsRef.current = projectWorktreeDiscoveryKey;
     void discoverWorktrees();
 
     return () => {
@@ -508,11 +552,29 @@ export const SessionSidebar: React.FC<SessionSidebarProps> = ({
     return [...sessions].sort((a, b) => compareSessionsByPinnedAndTime(a, b, pinnedSessionIds));
   }, [sessions, pinnedSessionIds]);
 
-  const sessionOrderIndex = React.useMemo(
-    () => new Map(sortedSessions.map((session, index) => [session.id, index])),
+  // Stable signature: id + updatedAt joined. When this string is
+  // unchanged, the relative ordering of sessions is identical and the
+  // derived `sessionOrderIndex` Map can return the previous reference.
+  // Without this, a fresh `sortedSessions` array (cheap to rebuild) would
+  // still hand a new Map identity to the entire SessionGroupSection
+  // memo chain, invalidating sourceGroupNodes, nodeBySessionId, and the
+  // rest of the down-stream useMemo chain.
+  const sessionOrderSignature = React.useMemo(
+    () => sortedSessions.map((s) => `${s.id}:${s.time?.updated ?? 0}`).join('|'),
     [sortedSessions],
   );
 
+  const sessionOrderIndexRef = React.useRef<{ signature: string; map: Map<string, number> } | null>(null);
+  const sessionOrderIndex = React.useMemo(() => {
+    const cached = sessionOrderIndexRef.current;
+    if (cached && cached.signature === sessionOrderSignature) {
+      return cached.map;
+    }
+    const next = new Map(sortedSessions.map((session, index) => [session.id, index]));
+    sessionOrderIndexRef.current = { signature: sessionOrderSignature, map: next };
+    return next;
+  }, [sessionOrderSignature, sortedSessions]);
+
   const childrenMap = React.useMemo(() => {
     const map = new Map<string, Session[]>();
     sortedSessions.forEach((session) => {
@@ -703,6 +765,16 @@ export const SessionSidebar: React.FC<SessionSidebarProps> = ({
     [collapsedFolderIds, toggleFolderCollapse, createFolder, t],
   );
 
+  const stableHandleSessionSelect = useStableRenderCallback(handleSessionSelect);
+  const stableHandleSessionDoubleClick = useStableRenderCallback(handleSessionDoubleClick);
+  const stableHandleSaveEdit = useStableRenderCallback(handleSaveEdit);
+  const stableHandleCancelEdit = useStableRenderCallback(handleCancelEdit);
+  const stableHandleShareSession = useStableRenderCallback(handleShareSession);
+  const stableHandleCopyShareUrl = useStableRenderCallback(handleCopyShareUrl);
+  const stableHandleUnshareSession = useStableRenderCallback(handleUnshareSession);
+  const stableHandleDeleteSession = useStableRenderCallback(handleDeleteSession);
+  const stableCreateFolderAndStartRename = useStableRenderCallback(createFolderAndStartRename);
+
   const showMoreGroupSessions = React.useCallback((groupId: string, currentVisibleCount: number) => {
     setVisibleSessionCountByGroup((prev) => {
       const next = new Map(prev);
@@ -881,6 +953,7 @@ export const SessionSidebar: React.FC<SessionSidebarProps> = ({
     sessions,
     archivedSessions,
     availableWorktreesByProject,
+    normalizedProjects,
   });
 
   useArchivedAutoFolders({
@@ -930,7 +1003,7 @@ export const SessionSidebar: React.FC<SessionSidebarProps> = ({
     </div>
   );
 
-  const { currentSessionDirectory } = useProjectSessionSelection({
+  useProjectSessionSelection({
     projectSections,
     activeProjectId,
     activeSessionByProject,
@@ -942,8 +1015,6 @@ export const SessionSidebar: React.FC<SessionSidebarProps> = ({
     openNewSessionDraft,
     setActiveMainTab,
     setSessionSwitcherOpen,
-    sessions,
-    worktreeMetadata,
   });
 
   const { getOrderedGroups } = useGroupOrdering(groupOrderByProject);
@@ -1214,15 +1285,16 @@ export const SessionSidebar: React.FC<SessionSidebarProps> = ({
     projectHeaderSentinelRefs,
   });
 
-  const renderSessionNode = React.useCallback(
+  const renderSessionNode = useStableRenderCallback(
     (
       node: SessionNode,
-      depth = 0,
+      depth: number = 0,
       groupDirectory?: string | null,
       projectId?: string | null,
-      archivedBucket = false,
+      archivedBucket: boolean = false,
       secondaryMeta?: { projectLabel?: string | null; branchLabel?: string | null } | null,
       renderContext: 'project' | 'recent' = 'project',
+      renderExtras?: SessionNodeRenderExtras,
     ): React.ReactNode => (
       <SessionNodeItem
         node={node}
@@ -1240,16 +1312,16 @@ export const SessionSidebar: React.FC<SessionSidebarProps> = ({
         setEditingId={setEditingId}
         editTitle={editTitle}
         setEditTitle={setEditTitle}
-        handleSaveEdit={handleSaveEdit}
-        handleCancelEdit={handleCancelEdit}
+        handleSaveEdit={stableHandleSaveEdit}
+        handleCancelEdit={stableHandleCancelEdit}
         toggleParent={toggleParent}
-        handleSessionSelect={handleSessionSelect}
-        handleSessionDoubleClick={handleSessionDoubleClick}
+        handleSessionSelect={stableHandleSessionSelect}
+        handleSessionDoubleClick={stableHandleSessionDoubleClick}
         togglePinnedSession={togglePinnedSession}
-        handleShareSession={handleShareSession}
+        handleShareSession={stableHandleShareSession}
         copiedSessionId={copiedSessionId}
-        handleCopyShareUrl={handleCopyShareUrl}
-        handleUnshareSession={handleUnshareSession}
+        handleCopyShareUrl={stableHandleCopyShareUrl}
+        handleUnshareSession={stableHandleUnshareSession}
         openSidebarMenuKey={openSidebarMenuKey}
         setOpenSidebarMenuKey={setOpenSidebarMenuKey}
         renamingFolderId={renamingFolderId}
@@ -1257,50 +1329,22 @@ export const SessionSidebar: React.FC<SessionSidebarProps> = ({
         getSessionFolderId={getSessionFolderId}
         removeSessionFromFolder={removeSessionFromFolder}
         addSessionToFolder={addSessionToFolder}
-        createFolderAndStartRename={createFolderAndStartRename}
+        createFolderAndStartRename={stableCreateFolderAndStartRename}
         openContextPanelTab={openContextPanelTab}
-        handleDeleteSession={handleDeleteSession}
+        handleDeleteSession={stableHandleDeleteSession}
         mobileVariant={mobileVariant}
         alwaysShowActions={alwaysShowSidebarActions}
         renderSessionNode={renderSessionNode}
         secondaryMeta={secondaryMeta}
         renderContext={renderContext}
+        subtreeContainsActive={renderExtras?.subtreeContainsActive ?? EMPTY_SUBTREE_SET}
+        subtreeContainsEditing={renderExtras?.subtreeContainsEditing ?? EMPTY_SUBTREE_SET}
+        menuOpenSessionId={renderExtras?.menuOpenSessionId ?? null}
+        nodeStructureKey={renderExtras?.nodeStructureKey ?? ''}
+        childRenderExtrasFor={renderExtras?.childRenderExtrasFor}
+        liveSessionById={liveSessionById}
       />
     ),
-    [
-      currentSessionId,
-      pinnedSessionIds,
-      expandedParents,
-      hasSessionSearchQuery,
-      normalizedSessionSearchQuery,
-      notifyOnSubtasks,
-      editingId,
-      setEditingId,
-      editTitle,
-      setEditTitle,
-      handleSaveEdit,
-      handleCancelEdit,
-      toggleParent,
-      handleSessionSelect,
-      handleSessionDoubleClick,
-      togglePinnedSession,
-      handleShareSession,
-      copiedSessionId,
-      handleCopyShareUrl,
-      handleUnshareSession,
-      openSidebarMenuKey,
-      setOpenSidebarMenuKey,
-      renamingFolderId,
-      getFoldersForScope,
-      getSessionFolderId,
-      removeSessionFromFolder,
-      addSessionToFolder,
-      createFolderAndStartRename,
-      openContextPanelTab,
-      handleDeleteSession,
-      mobileVariant,
-      alwaysShowSidebarActions,
-    ],
   );
 
   const toggleCollapsedGroup = React.useCallback((key: string) => {
@@ -1335,7 +1379,15 @@ export const SessionSidebar: React.FC<SessionSidebarProps> = ({
   }, [prVisualSummaryMap]);
 
   const renderGroupSessions = React.useCallback(
-    (group: SessionGroup, groupKey: string, projectId?: string | null, hideGroupLabel?: boolean, dragHandleProps?: SortableDragHandleProps | null, compactBodyPadding?: boolean) => (
+    (
+      group: SessionGroup,
+      groupKey: string,
+      projectId?: string | null,
+      hideGroupLabel?: boolean,
+      dragHandleProps?: SortableDragHandleProps | null,
+      compactBodyPadding?: boolean,
+      scrollContainerRef?: React.RefObject<HTMLElement | null>,
+    ) => (
       <SessionGroupSection
         group={group}
         groupKey={groupKey}
@@ -1355,7 +1407,6 @@ export const SessionSidebar: React.FC<SessionSidebarProps> = ({
         showDeletionDialog={showDeletionDialog}
         setDeleteFolderConfirm={setDeleteFolderConfirm}
         renderSessionNode={renderSessionNode}
-        currentSessionDirectory={currentSessionDirectory}
         projectRepoStatus={projectRepoStatus}
         lastRepoStatus={lastRepoStatusRef.current}
         showMoreGroupSessions={showMoreGroupSessions}
@@ -1368,16 +1419,23 @@ export const SessionSidebar: React.FC<SessionSidebarProps> = ({
         setSessionSwitcherOpen={setSessionSwitcherOpen}
         openNewSessionDraft={openNewSessionDraftFromTree}
         addSessionToFolder={addSessionToFolder}
-        createFolderAndStartRename={createFolderAndStartRename}
+        createFolderAndStartRename={stableCreateFolderAndStartRename}
         renamingFolderId={renamingFolderId}
         renameFolderDraft={renameFolderDraft}
         setRenameFolderDraft={setRenameFolderDraft}
         setRenamingFolderId={setRenamingFolderId}
         pinnedSessionIds={pinnedSessionIds}
+        expandedParents={expandedParents}
         sessionOrderIndex={sessionOrderIndex}
+        currentSessionId={currentSessionId}
+        editingId={editingId}
+        editTitle={editTitle}
+        openSidebarMenuKey={openSidebarMenuKey}
+        liveSessionById={liveSessionById}
         prVisualStateByDirectoryBranch={prVisualStateByDirectoryBranch}
         onToggleCollapsedGroup={toggleCollapsedGroup}
         dragHandleProps={dragHandleProps}
+        scrollContainerRef={scrollContainerRef}
       />
     ),
     [
@@ -1393,7 +1451,6 @@ export const SessionSidebar: React.FC<SessionSidebarProps> = ({
       deleteFolder,
       showDeletionDialog,
       renderSessionNode,
-      currentSessionDirectory,
       projectRepoStatus,
       showMoreGroupSessions,
       resetGroupSessionLimit,
@@ -1405,11 +1462,17 @@ export const SessionSidebar: React.FC<SessionSidebarProps> = ({
       setSessionSwitcherOpen,
       openNewSessionDraftFromTree,
       addSessionToFolder,
-      createFolderAndStartRename,
+      stableCreateFolderAndStartRename,
       renamingFolderId,
       renameFolderDraft,
       pinnedSessionIds,
+      expandedParents,
       sessionOrderIndex,
+      currentSessionId,
+      editingId,
+      editTitle,
+      openSidebarMenuKey,
+      liveSessionById,
       prVisualStateByDirectoryBranch,
       toggleCollapsedGroup,
     ],
@@ -1419,174 +1482,40 @@ export const SessionSidebar: React.FC<SessionSidebarProps> = ({
     <SidebarActivitySections
       sections={activitySections}
       renderSessionNode={renderSessionNode}
+      currentSessionId={currentSessionId}
+      editingId={editingId}
+      openSidebarMenuKey={openSidebarMenuKey}
       variant="section"
     />
   ) : null;
   const isInlineEditing = Boolean(renamingFolderId || editingId || editingProjectDialogId);
 
-  const selectionModeEnabled = useSessionMultiSelectStore((state) => state.enabled);
-  const selectedIds = useSessionMultiSelectStore((state) => state.selectedIds);
-  const selectionScopeKey = useSessionMultiSelectStore((state) => state.scopeKey);
-  const multiSelectStoreApi = useSessionMultiSelectStore;
-
-  const handleToggleSelectionMode = React.useCallback(() => {
-    useSessionMultiSelectStore.getState().toggleMode();
-  }, []);
-  const handleExitSelectionMode = React.useCallback(() => {
-    useSessionMultiSelectStore.getState().disable();
-  }, []);
-
-  const bulkScopeIsArchived = React.useMemo(() => {
-    if (selectedIds.size === 0) return false;
-    if (typeof document === 'undefined') return false;
-    let sawActive = false;
-    let sawArchived = false;
-    for (const id of selectedIds) {
-      const rows = document.querySelectorAll<HTMLElement>(`[data-session-row="${CSS.escape(id)}"]`);
-      for (const row of rows) {
-        if (row.getAttribute('data-session-archived') === '1') sawArchived = true;
-        else sawActive = true;
-      }
-    }
-    return sawArchived && !sawActive;
-  }, [selectedIds]);
-
-  const derivedSelectionScope = React.useMemo(() => {
-    if (selectionScopeKey) return selectionScopeKey;
-    if (selectedIds.size === 0) return null;
-    if (typeof document === 'undefined') return null;
-    for (const id of selectedIds) {
-      const row = document.querySelector<HTMLElement>(`[data-session-row="${CSS.escape(id)}"]`);
-      const scope = row?.getAttribute('data-session-scope');
-      if (scope && scope.length > 0) return scope;
-    }
-    return null;
-  }, [selectedIds, selectionScopeKey]);
-
-  const bulkScopeFolders = React.useMemo(() => {
-    if (!derivedSelectionScope) return [];
-    return foldersMap[derivedSelectionScope] ?? [];
-  }, [foldersMap, derivedSelectionScope]);
-
-  const bulkCanRemoveFromFolder = React.useMemo(() => {
-    if (!derivedSelectionScope || selectedIds.size === 0) return false;
-    const scopeFolders = foldersMap[derivedSelectionScope] ?? [];
-    for (const folder of scopeFolders) {
-      for (const id of folder.sessionIds) {
-        if (selectedIds.has(id)) return true;
-      }
-    }
-    return false;
-  }, [foldersMap, derivedSelectionScope, selectedIds]);
-
-  const handleBulkMoveToFolder = React.useCallback((folderId: string) => {
-    if (!derivedSelectionScope || selectedIds.size === 0) return;
-    addSessionsToFolder(derivedSelectionScope, folderId, Array.from(selectedIds));
-  }, [addSessionsToFolder, selectedIds, derivedSelectionScope]);
-
-  const handleBulkCreateFolderAndMove = React.useCallback(() => {
-    if (!derivedSelectionScope || selectedIds.size === 0) return;
-    const newFolder = createFolderAndStartRename(derivedSelectionScope);
-    if (!newFolder) return;
-    addSessionsToFolder(derivedSelectionScope, newFolder.id, Array.from(selectedIds));
-  }, [addSessionsToFolder, createFolderAndStartRename, selectedIds, derivedSelectionScope]);
-
-  const handleBulkRemoveFromFolder = React.useCallback(() => {
-    if (!derivedSelectionScope || selectedIds.size === 0) return;
-    removeSessionsFromFolders(derivedSelectionScope, Array.from(selectedIds));
-  }, [removeSessionsFromFolders, selectedIds, derivedSelectionScope]);
-
-  const executeBulkDelete = React.useCallback(async () => {
-    const ids = Array.from(selectedIds);
-    if (ids.length === 0) return;
-    if (bulkScopeIsArchived) {
-      const { deletedIds, failedIds } = await deleteSessions(ids);
-      if (deletedIds.length > 0) {
-        toast.success(deletedIds.length === 1
-          ? t('sessions.sidebar.bulkActions.deletedSingle', { count: deletedIds.length })
-          : t('sessions.sidebar.bulkActions.deletedPlural', { count: deletedIds.length }));
-      }
-      if (failedIds.length > 0) {
-        toast.error(failedIds.length === 1
-          ? t('sessions.sidebar.bulkActions.failedDeleteSingle', { count: failedIds.length })
-          : t('sessions.sidebar.bulkActions.failedDeletePlural', { count: failedIds.length }));
-      }
-    } else {
-      const { archivedIds, failedIds } = await archiveSessions(ids);
-      if (archivedIds.length > 0) {
-        toast.success(archivedIds.length === 1
-          ? t('sessions.sidebar.bulkActions.archivedSingle', { count: archivedIds.length })
-          : t('sessions.sidebar.bulkActions.archivedPlural', { count: archivedIds.length }));
-      }
-      if (failedIds.length > 0) {
-        toast.error(failedIds.length === 1
-          ? t('sessions.sidebar.bulkActions.failedArchiveSingle', { count: failedIds.length })
-          : t('sessions.sidebar.bulkActions.failedArchivePlural', { count: failedIds.length }));
-      }
-    }
-    useSessionMultiSelectStore.getState().clear();
-  }, [archiveSessions, bulkScopeIsArchived, deleteSessions, selectedIds, t]);
-
-  const handleBulkDelete = React.useCallback(() => {
-    const count = selectedIds.size;
-    if (count === 0) return;
-    if (!showDeletionDialog) {
-      void executeBulkDelete();
-      return;
-    }
-    setBulkDeleteConfirm({ sessionCount: count, archivedBucket: bulkScopeIsArchived });
-  }, [bulkScopeIsArchived, executeBulkDelete, selectedIds, showDeletionDialog]);
-
-  const confirmBulkDelete = React.useCallback(async () => {
-    setBulkDeleteConfirm(null);
-    await executeBulkDelete();
-  }, [executeBulkDelete]);
-
-  React.useEffect(() => {
-    if (!selectionModeEnabled) return;
-    const isMac = typeof navigator !== 'undefined' && /Macintosh|Mac OS X/.test(navigator.userAgent || '');
-    const listener = (event: KeyboardEvent) => {
-      if (isInlineEditing) return;
-      const target = event.target as HTMLElement | null;
-      if (target && (target.tagName === 'INPUT' || target.tagName === 'TEXTAREA' || target.isContentEditable)) {
-        return;
-      }
-      const modifier = isMac ? event.metaKey : event.ctrlKey;
-      if (event.key === 'Escape') {
-        event.preventDefault();
-        useSessionMultiSelectStore.getState().disable();
-        return;
-      }
-      if (modifier && event.key === 'Backspace') {
-        event.preventDefault();
-        handleBulkDelete();
-        return;
-      }
-      if (modifier && (event.key === 'a' || event.key === 'A')) {
-        const rows = typeof document !== 'undefined'
-          ? Array.from(document.querySelectorAll<HTMLElement>('[data-session-row]'))
-          : [];
-        if (rows.length === 0) return;
-        event.preventDefault();
-        const currentScope = multiSelectStoreApi.getState().scopeKey;
-        const targetScope = currentScope
-          ?? rows[0]?.getAttribute('data-session-scope')
-          ?? null;
-        const scopeFilter = (el: HTMLElement): boolean => {
-          if (!targetScope) return true;
-          return el.getAttribute('data-session-scope') === targetScope;
-        };
-        const ids = rows
-          .filter(scopeFilter)
-          .map((el) => el.getAttribute('data-session-row'))
-          .filter((id): id is string => typeof id === 'string' && id.length > 0);
-        if (ids.length === 0) return;
-        multiSelectStoreApi.getState().replaceAll(ids, targetScope || null);
-      }
-    };
-    window.addEventListener('keydown', listener);
-    return () => window.removeEventListener('keydown', listener);
-  }, [handleBulkDelete, isInlineEditing, multiSelectStoreApi, selectionModeEnabled]);
+  const {
+    selectionModeEnabled,
+    hasSelection,
+    selectedIdsSize,
+    bulkScopeIsArchived,
+    derivedSelectionScope,
+    bulkScopeFolders,
+    bulkCanRemoveFromFolder,
+    handleToggleSelectionMode,
+    handleExitSelectionMode,
+    handleBulkMoveToFolder,
+    handleBulkCreateFolderAndMove,
+    handleBulkRemoveFromFolder,
+    handleBulkDelete,
+    confirmBulkDelete,
+  } = useSidebarBulkActions({
+    isInlineEditing,
+    showDeletionDialog,
+    foldersMap,
+    addSessionsToFolder,
+    removeSessionsFromFolders,
+    createFolderAndStartRename,
+    archiveSessions,
+    deleteSessions,
+    setBulkDeleteConfirm,
+  });
   const handleOpenMultiRunFromHeader = React.useCallback(() => {
     setActiveMainTab('chat');
     if (mobileVariant) {
@@ -1670,9 +1599,9 @@ export const SessionSidebar: React.FC<SessionSidebarProps> = ({
         isInlineEditing={isInlineEditing}
       />
 
-      {selectionModeEnabled && selectedIds.size > 0 ? (
+      {selectionModeEnabled && hasSelection ? (
         <BulkActionBar
-          selectedCount={selectedIds.size}
+          selectedCount={selectedIdsSize}
           scopeKey={derivedSelectionScope}
           scopeFolders={bulkScopeFolders}
           archivedBucket={bulkScopeIsArchived}
diff --git a/packages/ui/src/components/session/sidebar/SessionGroupSection.tsx b/packages/ui/src/components/session/sidebar/SessionGroupSection.tsx
index f66157f9..cba33df1 100644
--- a/packages/ui/src/components/session/sidebar/SessionGroupSection.tsx
+++ b/packages/ui/src/components/session/sidebar/SessionGroupSection.tsx
@@ -5,6 +5,11 @@ import type { Session } from '@opencode-ai/sdk/v2';
 // Archived buckets routinely grow into the hundreds/thousands; virtualize
 // when we cross this row count so the DOM stays bounded.
 const ARCHIVED_VIRTUALIZE_THRESHOLD = 50;
+// Active/worktree groups can also grow large (a single worktree with 80+
+// sessions), and unlike the archive they're interactive from the start.
+// Virtualize eagerly for non-archived groups to keep the rendered row
+// count bounded. With overscan ~8 the visible behavior is identical.
+const ACTIVE_VIRTUALIZE_THRESHOLD = 30;
 // Compact rows in the archived bucket without nested subagents render
 // around 24-32px; virtua measures mounted rows and uses this as the initial hint.
 const ARCHIVED_ROW_ESTIMATE_PX = 28;
@@ -18,6 +23,13 @@ import { DroppableFolderWrapper, SessionFolderDndScope } from './sessionFolderDn
 import type { SortableDragHandleProps } from './sortableItems';
 import type { GroupSearchData, SessionGroup, SessionNode } from './types';
 import { compareSessionsByPinnedAndTime, isBranchDifferentFromLabel, normalizePath, renderHighlightedText } from './utils';
+import {
+  collectSubtreeContainingId,
+  computeNodeStructureKey,
+  nodeContainsSessionId,
+  resolveMenuOpenSessionId,
+} from './sessionNodeItemUtils';
+import type { SessionNodeRenderExtras } from './sessionNodeItemUtils';
 import type { SessionFolder } from '@/stores/useSessionFoldersStore';
 import { useSessionFoldersStore } from '@/stores/useSessionFoldersStore';
 import { useSessionDisplayStore } from '@/stores/useSessionDisplayStore';
@@ -50,8 +62,16 @@ type Props = {
   deleteFolder: (scopeKey: string, folderId: string) => void;
   showDeletionDialog: boolean;
   setDeleteFolderConfirm: React.Dispatch<React.SetStateAction<DeleteFolderConfirm>>;
-  renderSessionNode: (node: SessionNode, depth?: number, groupDirectory?: string | null, projectId?: string | null, archivedBucket?: boolean, secondaryMeta?: { projectLabel?: string | null; branchLabel?: string | null } | null) => React.ReactNode;
-  currentSessionDirectory: string | null;
+  renderSessionNode: (
+    node: SessionNode,
+    depth?: number,
+    groupDirectory?: string | null,
+    projectId?: string | null,
+    archivedBucket?: boolean,
+    secondaryMeta?: { projectLabel?: string | null; branchLabel?: string | null } | null,
+    renderContext?: 'project' | 'recent',
+    renderExtras?: SessionNodeRenderExtras,
+  ) => React.ReactNode;
   projectRepoStatus: Map<string, boolean | null>;
   lastRepoStatus: boolean;
   showMoreGroupSessions: (groupKey: string, currentVisibleCount: number) => void;
@@ -70,7 +90,13 @@ type Props = {
   setRenameFolderDraft: React.Dispatch<React.SetStateAction<string>>;
   setRenamingFolderId: React.Dispatch<React.SetStateAction<string | null>>;
   pinnedSessionIds: Set<string>;
+  expandedParents: Set<string>;
   sessionOrderIndex: Map<string, number>;
+  currentSessionId: string | null;
+  editingId: string | null;
+  editTitle: string;
+  openSidebarMenuKey: string | null;
+  liveSessionById: Map<string, Session>;
   prVisualStateByDirectoryBranch: Map<string, {
     visualState: 'draft' | 'open' | 'blocked' | 'merged' | 'closed';
     number: number;
@@ -97,9 +123,196 @@ type Props = {
   onToggleCollapsedGroup: (groupKey: string) => void;
   dragHandleProps?: SortableDragHandleProps | null;
   compactBodyPadding?: boolean;
+  /**
+   * Optional scroll container ref threaded from the outer ScrollableOverlay.
+   * When provided, the virtualization effect can resolve the scrolling
+   * ancestor synchronously and skip the getComputedStyle walk on every
+   * render of an expanded archived bucket.
+   */
+  scrollContainerRef?: React.RefObject<HTMLElement | null>;
 };
 
-export function SessionGroupSection(props: Props): React.ReactNode {
+const groupContainsSessionId = (group: SessionGroup, sessionId: string | null): boolean => {
+  if (!sessionId) return false;
+  return group.sessions.some((node) => nodeContainsSessionId(node, sessionId));
+};
+
+const groupHasPinnedMembershipChange = (
+  group: SessionGroup,
+  prevPinnedSessionIds: Set<string>,
+  nextPinnedSessionIds: Set<string>,
+): boolean => {
+  const visit = (node: SessionNode): boolean => {
+    const sessionId = node.session.id;
+    if (prevPinnedSessionIds.has(sessionId) !== nextPinnedSessionIds.has(sessionId)) return true;
+    return node.children.some(visit);
+  };
+  return group.sessions.some(visit);
+};
+
+const groupHasSessionOrderChange = (
+  group: SessionGroup,
+  prevSessionOrderIndex: Map<string, number>,
+  nextSessionOrderIndex: Map<string, number>,
+): boolean => {
+  const visit = (node: SessionNode): boolean => {
+    const sessionId = node.session.id;
+    if (prevSessionOrderIndex.get(sessionId) !== nextSessionOrderIndex.get(sessionId)) return true;
+    return node.children.some(visit);
+  };
+  return group.sessions.some(visit);
+};
+
+const groupHasExpansionMembershipChange = (
+  group: SessionGroup,
+  prevExpandedParents: Set<string>,
+  nextExpandedParents: Set<string>,
+): boolean => {
+  const bucketTag = group.isArchivedBucket ? 'archived' : 'active';
+  const visit = (node: SessionNode): boolean => {
+    const key = `project:${bucketTag}:${node.session.id}`;
+    if (prevExpandedParents.has(key) !== nextExpandedParents.has(key)) return true;
+    return node.children.some(visit);
+  };
+  return group.sessions.some(visit);
+};
+
+const groupHasResolvedSessionChange = (
+  group: SessionGroup,
+  prevLiveSessionById: Map<string, Session>,
+  nextLiveSessionById: Map<string, Session>,
+): boolean => {
+  const visit = (node: SessionNode): boolean => {
+    const sessionId = node.session.id;
+    if ((prevLiveSessionById.get(sessionId) ?? node.session) !== (nextLiveSessionById.get(sessionId) ?? node.session)) {
+      return true;
+    }
+    return node.children.some(visit);
+  };
+  return group.sessions.some(visit);
+};
+
+const getProjectRepoStatusValue = (props: Props): boolean | null | undefined => {
+  if (!props.projectId) return undefined;
+  return props.projectRepoStatus.has(props.projectId)
+    ? props.projectRepoStatus.get(props.projectId)
+    : undefined;
+};
+
+const areGroupPropsEqual = (prev: Props, next: Props): boolean => {
+  // Bail on Object.is for the props that drive the most work: the group
+  // itself, its key, and the group-level chrome. These change rarely and
+  // any change should force a re-render of this group.
+  if (prev.group !== next.group) return false;
+  if (prev.groupKey !== next.groupKey) return false;
+  if (prev.projectId !== next.projectId) return false;
+  if (prev.hideGroupLabel !== next.hideGroupLabel) return false;
+  if (prev.compactBodyPadding !== next.compactBodyPadding) return false;
+  if (prev.groupSearchDataByGroup !== next.groupSearchDataByGroup) return false;
+  if (prev.visibleSessionCount !== next.visibleSessionCount) return false;
+
+  if (prev.collapsedGroups !== next.collapsedGroups
+    && prev.collapsedGroups.has(prev.groupKey) !== next.collapsedGroups.has(next.groupKey)) {
+    return false;
+  }
+
+  if (prev.projectRepoStatus !== next.projectRepoStatus
+    && getProjectRepoStatusValue(prev) !== getProjectRepoStatusValue(next)) {
+    return false;
+  }
+
+  if (prev.pinnedSessionIds !== next.pinnedSessionIds
+    && groupHasPinnedMembershipChange(next.group, prev.pinnedSessionIds, next.pinnedSessionIds)) {
+    return false;
+  }
+
+  if (prev.expandedParents !== next.expandedParents
+    && groupHasExpansionMembershipChange(next.group, prev.expandedParents, next.expandedParents)) {
+    return false;
+  }
+
+  if (prev.sessionOrderIndex !== next.sessionOrderIndex
+    && groupHasSessionOrderChange(next.group, prev.sessionOrderIndex, next.sessionOrderIndex)) {
+    return false;
+  }
+
+  if (prev.currentSessionId !== next.currentSessionId
+    && (groupContainsSessionId(prev.group, prev.currentSessionId) || groupContainsSessionId(next.group, next.currentSessionId))) {
+    return false;
+  }
+
+  if (prev.editingId !== next.editingId
+    && (groupContainsSessionId(prev.group, prev.editingId) || groupContainsSessionId(next.group, next.editingId))) {
+    return false;
+  }
+
+  if (prev.editTitle !== next.editTitle
+    && (groupContainsSessionId(prev.group, prev.editingId) || groupContainsSessionId(next.group, next.editingId))) {
+    return false;
+  }
+
+  if (prev.openSidebarMenuKey !== next.openSidebarMenuKey) {
+    const prevMenuSessionId = resolveMenuOpenSessionId(prev.group.sessions, prev.openSidebarMenuKey, 'project', Boolean(prev.group.isArchivedBucket));
+    const nextMenuSessionId = resolveMenuOpenSessionId(next.group.sessions, next.openSidebarMenuKey, 'project', Boolean(next.group.isArchivedBucket));
+    if (prevMenuSessionId || nextMenuSessionId) return false;
+  }
+
+  if (prev.liveSessionById !== next.liveSessionById
+    && groupHasResolvedSessionChange(next.group, prev.liveSessionById, next.liveSessionById)) {
+    return false;
+  }
+
+  // Per-row / per-state props. The PR-visual-state map flips frequently
+  // during bootstrap but a single group's value is usually stable, so we
+  // compare only the value this group actually consumes instead of the
+  // whole map reference.
+  if (prev.prVisualStateByDirectoryBranch !== next.prVisualStateByDirectoryBranch) {
+    const prevVal = prev.group?.directory && prev.group?.branch
+      ? prev.prVisualStateByDirectoryBranch.get(`${prev.group.directory}::${prev.group.branch.trim()}`)
+      : undefined;
+    const nextVal = next.group?.directory && next.group?.branch
+      ? next.prVisualStateByDirectoryBranch.get(`${next.group.directory}::${next.group.branch.trim()}`)
+      : undefined;
+    if (!Object.is(prevVal, nextVal)) return false;
+  }
+
+  // Other props are typically stable references from the parent. Default
+  // to reference equality (the cheap path) and only re-render when the
+  // parent actually swapped something.
+  return (
+    prev.hasSessionSearchQuery === next.hasSessionSearchQuery
+    && prev.normalizedSessionSearchQuery === next.normalizedSessionSearchQuery
+    && prev.hideDirectoryControls === next.hideDirectoryControls
+    && prev.collapsedFolderIds === next.collapsedFolderIds
+    && prev.toggleFolderCollapse === next.toggleFolderCollapse
+    && prev.renameFolder === next.renameFolder
+    && prev.deleteFolder === next.deleteFolder
+    && prev.showDeletionDialog === next.showDeletionDialog
+    && prev.setDeleteFolderConfirm === next.setDeleteFolderConfirm
+    && prev.renderSessionNode === next.renderSessionNode
+    && prev.lastRepoStatus === next.lastRepoStatus
+    && prev.showMoreGroupSessions === next.showMoreGroupSessions
+    && prev.resetGroupSessionLimit === next.resetGroupSessionLimit
+    && prev.mobileVariant === next.mobileVariant
+    && prev.alwaysShowActions === next.alwaysShowActions
+    && prev.activeProjectId === next.activeProjectId
+    && prev.setActiveProjectIdOnly === next.setActiveProjectIdOnly
+    && prev.setActiveMainTab === next.setActiveMainTab
+    && prev.setSessionSwitcherOpen === next.setSessionSwitcherOpen
+    && prev.openNewSessionDraft === next.openNewSessionDraft
+    && prev.addSessionToFolder === next.addSessionToFolder
+    && prev.createFolderAndStartRename === next.createFolderAndStartRename
+    && prev.renamingFolderId === next.renamingFolderId
+    && prev.renameFolderDraft === next.renameFolderDraft
+    && prev.setRenameFolderDraft === next.setRenameFolderDraft
+    && prev.setRenamingFolderId === next.setRenamingFolderId
+    && prev.onToggleCollapsedGroup === next.onToggleCollapsedGroup
+    && prev.dragHandleProps === next.dragHandleProps
+    && prev.scrollContainerRef === next.scrollContainerRef
+  );
+};
+
+function SessionGroupSectionBase(props: Props): React.ReactNode {
   const { t } = useI18n();
   const {
     group,
@@ -138,10 +351,14 @@ export function SessionGroupSection(props: Props): React.ReactNode {
     setRenamingFolderId,
     pinnedSessionIds,
     sessionOrderIndex,
+    currentSessionId,
+    editingId,
+    openSidebarMenuKey,
     prVisualStateByDirectoryBranch,
     onToggleCollapsedGroup,
     dragHandleProps,
     compactBodyPadding = false,
+    scrollContainerRef,
   } = props;
 
   const compareSessionNodes = React.useCallback((a: SessionNode, b: SessionNode) => {
@@ -254,6 +471,79 @@ export function SessionGroupSection(props: Props): React.ReactNode {
   const ungroupedSessions = React.useMemo(() => sourceGroupNodes.filter((node) => !sessionIdsInFolders.has(node.session.id)), [sourceGroupNodes, sessionIdsInFolders]);
   const rootFolders = React.useMemo(() => allFoldersForGroup.filter(({ folder }) => !folder.parentId), [allFoldersForGroup]);
 
+  // Precompute per-row "subtree contains active session" and "subtree contains
+  // editing session" lookups once per render. The previous design walked the
+  // node tree inside SessionNodeItem.areEqual for every row, which is O(M^2)
+  // across the whole sidebar. These sets let areEqual answer with a single
+  // Set.has lookup, so the cost is O(M) once per SessionGroupSection render.
+  const renderContextForGroup = 'project' as const;
+  const subtreeContainsActive = React.useMemo(() => {
+    const set = new Set<string>();
+    collectSubtreeContainingId(sourceGroupNodes, currentSessionId, set);
+    allFoldersForGroup.forEach(({ nodes }) => {
+      collectSubtreeContainingId(nodes, currentSessionId, set);
+    });
+    return set;
+  }, [sourceGroupNodes, allFoldersForGroup, currentSessionId]);
+
+  const subtreeContainsEditing = React.useMemo(() => {
+    const set = new Set<string>();
+    collectSubtreeContainingId(sourceGroupNodes, editingId, set);
+    allFoldersForGroup.forEach(({ nodes }) => {
+      collectSubtreeContainingId(nodes, editingId, set);
+    });
+    return set;
+  }, [sourceGroupNodes, allFoldersForGroup, editingId]);
+
+  const menuOpenSessionId = React.useMemo(() => {
+    if (!openSidebarMenuKey) return null;
+    const fromSource = resolveMenuOpenSessionId(sourceGroupNodes, openSidebarMenuKey, renderContextForGroup, Boolean(group.isArchivedBucket));
+    if (fromSource) return fromSource;
+    for (const { nodes } of allFoldersForGroup) {
+      const id = resolveMenuOpenSessionId(nodes, openSidebarMenuKey, renderContextForGroup, Boolean(group.isArchivedBucket));
+      if (id) return id;
+    }
+    return null;
+  }, [openSidebarMenuKey, sourceGroupNodes, allFoldersForGroup, group.isArchivedBucket]);
+
+  const buildNodeStructureKeyByNode = React.useCallback((nodes: SessionNode[]): WeakMap<SessionNode, string> => {
+    const map = new WeakMap<SessionNode, string>();
+    const visit = (node: SessionNode): void => {
+      map.set(node, computeNodeStructureKey(node));
+      for (const child of node.children) {
+        visit(child);
+      }
+    };
+    nodes.forEach(visit);
+    return map;
+  }, []);
+
+  const nodeStructureKeyBySourceNode = React.useMemo(
+    () => buildNodeStructureKeyByNode(sourceGroupNodes),
+    [buildNodeStructureKeyByNode, sourceGroupNodes],
+  );
+  const nodeStructureKeyByFolderNode = React.useMemo(
+    () => {
+      const map = new WeakMap<SessionNode, string>();
+      allFoldersForGroup.forEach(({ nodes }) => {
+        nodes.forEach((node) => map.set(node, computeNodeStructureKey(node)));
+      });
+      return map;
+    },
+    [allFoldersForGroup],
+  );
+
+  const resolveNodeStructureKey = React.useCallback((node: SessionNode): string => {
+    return nodeStructureKeyBySourceNode.get(node) ?? nodeStructureKeyByFolderNode.get(node) ?? '';
+  }, [nodeStructureKeyBySourceNode, nodeStructureKeyByFolderNode]);
+
+  const childRenderExtrasFor = React.useCallback((child: SessionNode) => ({
+    subtreeContainsActive,
+    subtreeContainsEditing,
+    menuOpenSessionId,
+    nodeStructureKey: resolveNodeStructureKey(child),
+  }), [subtreeContainsActive, subtreeContainsEditing, menuOpenSessionId, resolveNodeStructureKey]);
+
   const totalSessions = ungroupedSessions.length;
   const visibleSessions = group.isArchivedBucket
     ? ungroupedSessions
@@ -263,15 +553,21 @@ export function SessionGroupSection(props: Props): React.ReactNode {
   const remainingCount = totalSessions - visibleSessions.length;
   const canShowLess = !group.isArchivedBucket && !hasSessionSearchQuery && totalSessions > maxVisible && remainingCount === 0;
 
-  // Virtualize the archived bucket once it grows past a threshold. The
-  // archived list is the only group that can routinely hit hundreds or
-  // thousands of rows (projects accumulate archived sessions over time);
-  // every other group renders eagerly because they're small. All hooks
-  // below MUST stay above the search-empty early-return so they fire in
-  // the same order every render — rules-of-hooks.
+  // Virtualize large groups. Archived buckets grow into the hundreds or
+  // thousands of rows; active/worktree groups can also hit 80+ sessions
+  // when a single worktree accumulates over time. Both paths share the
+  // same virtua Virtualizer; the threshold just controls when we mount
+  // it. The visible behavior is identical because virtua uses overscan
+  // (8) for the buffer zone. All hooks below MUST stay above the
+  // search-empty early-return so they fire in the same order every
+  // render — rules-of-hooks.
   const shouldVirtualizeArchived = group.isArchivedBucket === true
     && !hasSessionSearchQuery
     && visibleSessions.length >= ARCHIVED_VIRTUALIZE_THRESHOLD;
+  const shouldVirtualizeActive = group.isArchivedBucket !== true
+    && !hasSessionSearchQuery
+    && visibleSessions.length >= ACTIVE_VIRTUALIZE_THRESHOLD;
+  const shouldVirtualize = shouldVirtualizeArchived || shouldVirtualizeActive;
 
   const archivedVirtualContainerRef = React.useRef<HTMLDivElement | null>(null);
   const archivedScrollRef = React.useRef<HTMLElement | null>(null);
@@ -284,22 +580,31 @@ export function SessionGroupSection(props: Props): React.ReactNode {
   // element and renders rows in the wrong subset / position.
   const [archivedScrollMargin, setArchivedScrollMargin] = React.useState(0);
 
-  // Find the nearest scrolling ancestor by walking up the DOM. The sidebar
-  // routes its scroll through `ScrollableOverlay` higher up the tree;
-  // threading a ref through every intermediate component would be invasive
-  // for this single use case.
-  // Resolve the scrolling ancestor and measure the virtual container's offset
-  // from its content origin, both on every render. The container ref is null
-  // while the archived bucket is collapsed (the body isn't mounted), so a
+  // Resolve the scrolling ancestor. When the parent has threaded a
+  // `scrollContainerRef` (Layer 1.4), use it directly to skip the
+  // `getComputedStyle` walk on every render of an expanded archived
+  // bucket — the walk is one of the more expensive operations in the
+  // hot path because it forces a style recalc on every parent up the
+  // tree. Fall back to the legacy walk only when the ref is missing.
+  //
+  // We also still re-run when the archive flips between expanded/collapsed,
+  // and on a ResizeObserver-driven layout change of the container, so a
   // dep-gated effect that only fires when shouldVirtualizeArchived flips
-  // would miss the eventual mount and leave the scroll element null forever.
-  // Running on every render lets us pick up the container as soon as
-  // expanding the bucket mounts it; the cached scroll element is reused as
-  // long as it still contains the container. Both state setters compare
-  // before writing, so a stable layout produces no state churn.
+  // would miss the eventual mount and leave the scroll element null.
+  const [, setLayoutVersion] = React.useState(0);
+  React.useEffect(() => {
+    if (!shouldVirtualize) return;
+    const container = archivedVirtualContainerRef.current;
+    if (!container) return;
+    if (typeof ResizeObserver === 'undefined') return;
+    const ro = new ResizeObserver(() => setLayoutVersion((v) => v + 1));
+    ro.observe(container);
+    return () => ro.disconnect();
+  }, [shouldVirtualize]);
+
   // eslint-disable-next-line react-hooks/exhaustive-deps
   React.useLayoutEffect(() => {
-    if (!shouldVirtualizeArchived) {
+    if (!shouldVirtualize) {
       if (archivedScrollEl !== null) setArchivedScrollEl(null);
       archivedScrollRef.current = null;
       if (archivedScrollMargin !== 0) setArchivedScrollMargin(0);
@@ -312,7 +617,15 @@ export function SessionGroupSection(props: Props): React.ReactNode {
       return;
     }
     let scrollEl: HTMLElement | null = archivedScrollEl;
-    if (!scrollEl || !scrollEl.contains(container)) {
+    const providedScrollEl = scrollContainerRef?.current ?? null;
+    if (providedScrollEl && providedScrollEl.contains(container)) {
+      scrollEl = providedScrollEl;
+      if (scrollEl !== archivedScrollEl) {
+        archivedScrollRef.current = scrollEl;
+        setArchivedScrollEl(scrollEl);
+        return;
+      }
+    } else if (!scrollEl || !scrollEl.contains(container)) {
       // Walk up to find the nearest scrolling ancestor. Only happens on
       // first mount or if the DOM tree restructured.
       let el: HTMLElement | null = container.parentElement;
@@ -327,8 +640,6 @@ export function SessionGroupSection(props: Props): React.ReactNode {
       if (scrollEl !== archivedScrollEl) {
         archivedScrollRef.current = scrollEl;
         setArchivedScrollEl(scrollEl);
-        // setState triggers a re-render; bail out and let the next pass
-        // measure the margin against the fresh element.
         return;
       }
     }
@@ -339,11 +650,9 @@ export function SessionGroupSection(props: Props): React.ReactNode {
     setArchivedScrollMargin((prev) => (Math.abs(prev - offset) < 1 ? prev : offset));
   });
 
-  if (hasSessionSearchQuery && !groupMatchesSearch && rootFolders.length === 0 && ungroupedSessions.length === 0) {
-    return null;
-  }
-
-  const collectGroupSessions = (nodes: SessionNode[]): Session[] => {
+  // Hooks below MUST stay above the search-empty early-return so they
+  // fire in the same order every render — rules-of-hooks.
+  const collectGroupSessions = React.useCallback((nodes: SessionNode[]): Session[] => {
     const collected: Session[] = [];
     const visit = (list: SessionNode[]) => {
       list.forEach((node) => {
@@ -353,9 +662,52 @@ export function SessionGroupSection(props: Props): React.ReactNode {
     };
     visit(nodes);
     return collected;
-  };
+  }, []);
+
+  // The "delete all in group" handler closes over the full list of
+  // sessions in this group. Memoize so the recursive flatten only runs
+  // when the underlying source group nodes change, not on every render.
+  const allGroupSessions = React.useMemo(
+    () => (group.isArchivedBucket ? collectGroupSessions(sourceGroupNodes) : []),
+    [collectGroupSessions, sourceGroupNodes, group.isArchivedBucket],
+  );
+
+  // Precompute the per-folder "delete all sessions in folder" list once
+  // per render. The previous design ran a recursive `collectFolderSessions`
+  // walk inside each folder's render, which is O(F × (S + F)) per group
+  // render. With F=50 folders and S=200 archived sessions this is
+  // significant; the precompute makes it O(F + S) once.
+  const folderSessionsForDeleteById = React.useMemo(() => {
+    if (!group.isArchivedBucket) return new Map<string, Session[]>();
+    const result = new Map<string, Session[]>();
+    const childIdsByParentId = new Map<string, string[]>();
+    for (const { folder } of allFoldersForGroup) {
+      if (!folder.parentId) continue;
+      const existing = childIdsByParentId.get(folder.parentId) ?? [];
+      existing.push(folder.id);
+      childIdsByParentId.set(folder.parentId, existing);
+    }
+    const visit = (targetFolderId: string, seen: Set<string>): Session[] => {
+      if (seen.has(targetFolderId)) return [];
+      seen.add(targetFolderId);
+      const directEntry = allFoldersForGroup.find(({ folder: candidate }) => candidate.id === targetFolderId);
+      const collected: Session[] = directEntry ? collectGroupSessions(directEntry.nodes) : [];
+      const childIds = childIdsByParentId.get(targetFolderId) ?? [];
+      for (const childId of childIds) {
+        collected.push(...visit(childId, seen));
+      }
+      return collected;
+    };
+    for (const { folder } of allFoldersForGroup) {
+      result.set(folder.id, visit(folder.id, new Set()));
+    }
+    return result;
+  }, [allFoldersForGroup, collectGroupSessions, group.isArchivedBucket]);
+
+  if (hasSessionSearchQuery && !groupMatchesSearch && rootFolders.length === 0 && ungroupedSessions.length === 0) {
+    return null;
+  }
 
-  const allGroupSessions = collectGroupSessions(sourceGroupNodes);
   const isGitProject = projectId && projectRepoStatus.has(projectId)
     ? Boolean(projectRepoStatus.get(projectId))
     : lastRepoStatus;
@@ -437,15 +789,7 @@ export function SessionGroupSection(props: Props): React.ReactNode {
     const subFolderItems = directSubFolders.length > 0
       ? <>{directSubFolders.map(({ folder: sf, nodes: sn }) => renderOneFolderItem(sf, sn, depth + 1))}</>
       : undefined;
-    const collectFolderSessions = (targetFolderId: string): Session[] => {
-      const directNodes = allFoldersForGroup.find(({ folder: candidate }) => candidate.id === targetFolderId)?.nodes ?? [];
-      const childFolders = allFoldersForGroup.filter(({ folder: candidate }) => candidate.parentId === targetFolderId);
-      return [
-        ...collectGroupSessions(directNodes),
-        ...childFolders.flatMap(({ folder: child }) => collectFolderSessions(child.id)),
-      ];
-    };
-    const folderSessionsForDelete = group.isArchivedBucket ? collectFolderSessions(folder.id) : [];
+    const folderSessionsForDelete = folderSessionsForDeleteById.get(folder.id) ?? [];
 
     return (
       <DroppableFolderWrapper key={folder.id} folderId={folder.id}>
@@ -485,6 +829,15 @@ export function SessionGroupSection(props: Props): React.ReactNode {
               });
             }}
             renderSessionNode={renderSessionNode}
+            getRenderExtras={resolveNodeStructureKey
+              ? (node) => ({
+                subtreeContainsActive,
+                subtreeContainsEditing,
+                menuOpenSessionId,
+                nodeStructureKey: resolveNodeStructureKey(node),
+                childRenderExtrasFor,
+              })
+              : undefined}
             groupDirectory={group.directory}
             projectId={projectId}
             mobileVariant={mobileVariant}
@@ -546,7 +899,7 @@ export function SessionGroupSection(props: Props): React.ReactNode {
       }}
     >
       {renderFolderItems()}
-      {shouldVirtualizeArchived ? (
+      {shouldVirtualize ? (
         <div ref={archivedVirtualContainerRef}>
           <Virtualizer
             data={visibleSessions}
@@ -555,11 +908,23 @@ export function SessionGroupSection(props: Props): React.ReactNode {
             scrollRef={archivedScrollRef}
             startMargin={archivedScrollMargin}
           >
-            {(node) => renderSessionNode(node, 0, group.directory, projectId, true) as React.ReactElement}
+            {(node) => renderSessionNode(node, 0, group.directory, projectId, group.isArchivedBucket === true, undefined, 'project', {
+              subtreeContainsActive,
+              subtreeContainsEditing,
+              menuOpenSessionId,
+              nodeStructureKey: resolveNodeStructureKey(node),
+              childRenderExtrasFor,
+            }) as React.ReactElement}
           </Virtualizer>
         </div>
       ) : (
-        visibleSessions.map((node) => renderSessionNode(node, 0, group.directory, projectId, group.isArchivedBucket === true))
+        visibleSessions.map((node) => renderSessionNode(node, 0, group.directory, projectId, group.isArchivedBucket === true, undefined, 'project', {
+          subtreeContainsActive,
+          subtreeContainsEditing,
+          menuOpenSessionId,
+          nodeStructureKey: resolveNodeStructureKey(node),
+          childRenderExtrasFor,
+        }))
       )}
       {totalSessions === 0 && allFoldersForGroup.length === 0 ? (
         <div className="py-1 text-left typography-micro text-muted-foreground">
@@ -846,3 +1211,5 @@ export function SessionGroupSection(props: Props): React.ReactNode {
     </div>
   );
 }
+
+export const SessionGroupSection = React.memo(SessionGroupSectionBase, areGroupPropsEqual);
diff --git a/packages/ui/src/components/session/sidebar/SessionNodeItem.tsx b/packages/ui/src/components/session/sidebar/SessionNodeItem.tsx
index 5db883a5..75703af0 100644
--- a/packages/ui/src/components/session/sidebar/SessionNodeItem.tsx
+++ b/packages/ui/src/components/session/sidebar/SessionNodeItem.tsx
@@ -21,10 +21,12 @@ import { Dialog, DialogContent, DialogDescription, DialogFooter, DialogHeader, D
 import { Icon } from "@/components/icon/Icon";
 import { buildExportFilename, downloadAsMarkdown, formatSessionAsMarkdown, getExportRevealLabelKey, revealExportedMarkdown, saveAsMarkdownDesktop } from '@/lib/exportSession';
 import type { ChildSessionExport } from '@/lib/exportSession';
-import { buildSessionMessageRecordsSnapshot, useDirectoryStore, useGlobalSessionStatus, useSession, useSessionPermissions } from '@/sync/sync-context';
+import { buildSessionMessageRecordsSnapshot, useDirectoryStore, useGlobalSessionStatus, useSessionPermissions } from '@/sync/sync-context';
 import { useSync } from '@/sync/use-sync';
 import { useViewportStore, viewportSessionKey } from '@/sync/viewport-store';
 import { DraggableSessionRow } from './sessionFolderDnd';
+import { nodeContainsSessionId } from './sessionNodeItemUtils';
+import type { SessionNodeChildRenderExtras, SessionNodeRenderExtras } from './sessionNodeItemUtils';
 import type { SessionNode } from './types';
 import { formatSessionCompactDateLabel, formatSessionDateLabel, normalizePath, renderHighlightedText } from './utils';
 import { useSessionDisplayStore } from '@/stores/useSessionDisplayStore';
@@ -61,7 +63,7 @@ type Props = {
   setEditingId: (id: string | null) => void;
   editTitle: string;
   setEditTitle: (value: string) => void;
-  handleSaveEdit: () => void;
+  handleSaveEdit: (titleOverride?: string) => void;
   handleCancelEdit: () => void;
   toggleParent: (expansionKey: string) => void;
   handleSessionSelect: (sessionId: string, sessionDirectory: string | null, projectId?: string | null) => void;
@@ -83,133 +85,58 @@ type Props = {
   handleDeleteSession: (session: Session, source?: { archivedBucket?: boolean; hardDelete?: boolean }) => void;
   mobileVariant: boolean;
   alwaysShowActions: boolean;
-  renderSessionNode: (node: SessionNode, depth?: number, groupDirectory?: string | null, projectId?: string | null, archivedBucket?: boolean, secondaryMeta?: SecondaryMeta | null, renderContext?: 'project' | 'recent') => React.ReactNode;
+  renderSessionNode: (
+    node: SessionNode,
+    depth?: number,
+    groupDirectory?: string | null,
+    projectId?: string | null,
+    archivedBucket?: boolean,
+    secondaryMeta?: SecondaryMeta | null,
+    renderContext?: 'project' | 'recent',
+    renderExtras?: SessionNodeRenderExtras,
+  ) => React.ReactNode;
   secondaryMeta?: SecondaryMeta | null;
   renderContext?: 'project' | 'recent';
-};
-
-const getNodeChildSignature = (node: SessionNode): string => {
-  if (node.children.length === 0) {
-    return '';
-  }
-
-  return node.children
-    .map((child) => `${child.session.id}:${child.children.length}`)
-    .join('|');
-};
-
-const treeContainsSessionId = (node: SessionNode, sessionId: string | null): boolean => {
-  if (!sessionId) {
-    return false;
-  }
-
-  if (node.session.id === sessionId) {
-    return true;
-  }
-
-  for (const child of node.children) {
-    if (treeContainsSessionId(child, sessionId)) {
-      return true;
-    }
-  }
-
-  return false;
-};
-
-const treeContainsMenuKey = (
-  node: SessionNode,
-  menuKey: string | null,
-  renderContext: 'project' | 'recent',
-  archivedBucket: boolean,
-): boolean => {
-  if (!menuKey) {
-    return false;
-  }
-
-  const nodeMenuKey = `${renderContext}:${archivedBucket ? 'archived' : 'active'}:${node.session.id}`;
-  if (nodeMenuKey === menuKey) {
-    return true;
-  }
-
-  for (const child of node.children) {
-    if (treeContainsMenuKey(child, menuKey, renderContext, archivedBucket)) {
-      return true;
-    }
-  }
-
-  return false;
-};
-
-const areEqual = (prev: Props, next: Props): boolean => {
-  const prevSession = prev.node.session;
-  const nextSession = next.node.session;
-  const prevSessionId = prevSession.id;
-  const nextSessionId = nextSession.id;
-
-  if (prevSessionId !== nextSessionId) return false;
-  if (prev.node.session !== next.node.session) return false;
-  if (getNodeChildSignature(prev.node) !== getNodeChildSignature(next.node)) return false;
-  if (prev.depth !== next.depth) return false;
-  if (prev.groupDirectory !== next.groupDirectory) return false;
-  if (prev.projectId !== next.projectId) return false;
-  if (prev.archivedBucket !== next.archivedBucket) return false;
-  if (prev.currentSessionId !== next.currentSessionId) {
-    const prevActiveInTree = treeContainsSessionId(prev.node, prev.currentSessionId);
-    const nextActiveInTree = treeContainsSessionId(next.node, next.currentSessionId);
-    if (prevActiveInTree || nextActiveInTree) {
-      return false;
-    }
-  }
-  if (prev.pinnedSessionIds.has(prevSessionId) !== next.pinnedSessionIds.has(nextSessionId)) return false;
-  // Expansion is keyed per render context, so compare the composite key
-  // matching the one isExpanded reads from in render. If a session appears
-  // in two contexts (project + recent), they have independent state.
-  {
-    const prevRenderContext = prev.renderContext ?? 'project';
-    const nextRenderContext = next.renderContext ?? 'project';
-    const prevArchived = prev.archivedBucket ?? false;
-    const nextArchived = next.archivedBucket ?? false;
-    const prevExpansionKey = `${prevRenderContext}:${prevArchived ? 'archived' : 'active'}:${prevSessionId}`;
-    const nextExpansionKey = `${nextRenderContext}:${nextArchived ? 'archived' : 'active'}:${nextSessionId}`;
-    if (prev.expandedParents.has(prevExpansionKey) !== next.expandedParents.has(nextExpansionKey)) return false;
-  }
-  if (prev.hasSessionSearchQuery !== next.hasSessionSearchQuery) return false;
-  if (prev.normalizedSessionSearchQuery !== next.normalizedSessionSearchQuery) return false;
-  if (prev.notifyOnSubtasks !== next.notifyOnSubtasks) return false;
-  if (prev.editingId !== next.editingId) {
-    const prevEditingInTree = treeContainsSessionId(prev.node, prev.editingId);
-    const nextEditingInTree = treeContainsSessionId(next.node, next.editingId);
-    if (prevEditingInTree || nextEditingInTree) {
-      return false;
-    }
-  }
-  if (prev.editTitle !== next.editTitle) {
-    const prevEditingInTree = treeContainsSessionId(prev.node, prev.editingId);
-    const nextEditingInTree = treeContainsSessionId(next.node, next.editingId);
-    if (prevEditingInTree || nextEditingInTree) {
-      return false;
-    }
-  }
-  if ((prev.copiedSessionId === prevSessionId) !== (next.copiedSessionId === nextSessionId)) return false;
-
-  const prevMenuInTree = treeContainsMenuKey(prev.node, prev.openSidebarMenuKey, prev.renderContext ?? 'project', prev.archivedBucket ?? false);
-  const nextMenuInTree = treeContainsMenuKey(next.node, next.openSidebarMenuKey, next.renderContext ?? 'project', next.archivedBucket ?? false);
-  if (prevMenuInTree !== nextMenuInTree) return false;
-
-  const prevDirectory = normalizePath((prevSession as Session & { directory?: string | null }).directory ?? null)
-    ?? normalizePath(prev.groupDirectory ?? null);
-  const nextDirectory = normalizePath((nextSession as Session & { directory?: string | null }).directory ?? null)
-    ?? normalizePath(next.groupDirectory ?? null);
-  if (prevDirectory !== nextDirectory) return false;
-
-  if ((prev.secondaryMeta?.projectLabel ?? null) !== (next.secondaryMeta?.projectLabel ?? null)) return false;
-  if ((prev.secondaryMeta?.branchLabel ?? null) !== (next.secondaryMeta?.branchLabel ?? null)) return false;
-  if (prev.mobileVariant !== next.mobileVariant) return false;
-  if (prev.alwaysShowActions !== next.alwaysShowActions) return false;
-  if ((prev.renderContext ?? 'project') !== (next.renderContext ?? 'project')) return false;
-  if (prev.renamingFolderId !== next.renamingFolderId) return false;
-
-  return true;
+  /**
+   * Precomputed set of session IDs whose subtree contains the current
+   * active session. Computed once per SessionGroupSection render (when
+   * currentSessionId changes) instead of being recomputed in every row's
+   * React.memo comparator.
+   */
+  subtreeContainsActive: Set<string>;
+  /**
+   * Precomputed set of session IDs whose subtree contains the session
+   * currently being edited. Same rationale as subtreeContainsActive.
+   */
+  subtreeContainsEditing: Set<string>;
+  /**
+   * Precomputed session ID of the row whose sidebar menu is open, or null
+   * if no menu is open. Only one row can have its menu open at a time.
+   */
+  menuOpenSessionId: string | null;
+  /**
+   * Precomputed structural key for this node. Encodes the IDs and child
+   * counts of all descendants so a reference-only change to `node` (e.g.
+   * a fresh tree rebuild) can be detected with a single string compare
+   * instead of a recursive walk per row.
+   */
+  nodeStructureKey: string;
+  /**
+   * Resolves the per-row render extras for each child node. SessionGroupSection
+   * walks the whole tree once to precompute the structure key for every
+   * descendant; SessionNodeItem's recursive child render uses this lookup
+   * to fetch the right key for each child it produces.
+   */
+  childRenderExtrasFor?: (child: SessionNode) => SessionNodeChildRenderExtras;
+  /**
+   * Batched index of live session objects keyed by id. The previous
+   * implementation called `useSession(session.id)` per row, which used
+   * `findLiveSession` to iterate every child-store on every SSE event.
+   * With M visible rows that's M×child-stores per event; the batched
+   * map turns it into a single Map.get per row. The parent falls back
+   * to `useSession` only when this map returns undefined.
+   */
+  liveSessionById: Map<string, Session>;
 };
 
 function SessionNodeItemComponent(props: Props): React.ReactNode {
@@ -255,6 +182,11 @@ function SessionNodeItemComponent(props: Props): React.ReactNode {
     renderSessionNode,
     secondaryMeta,
     renderContext = 'project',
+    subtreeContainsActive,
+    subtreeContainsEditing,
+    menuOpenSessionId,
+    childRenderExtrasFor,
+    liveSessionById,
   } = props;
   const hasSecondaryProjectLabel = Boolean(secondaryMeta?.projectLabel);
   const hasSecondaryBranchLabel = Boolean(secondaryMeta?.branchLabel);
@@ -302,11 +234,21 @@ function SessionNodeItemComponent(props: Props): React.ReactNode {
   const pendingRenameRef = React.useRef<{ id: string; title: string } | null>(null);
   const handleSaveEditRef = React.useRef(handleSaveEdit);
   handleSaveEditRef.current = handleSaveEdit;
+  const [renameDraft, setRenameDraft] = React.useState(editTitle);
+  const renameDraftRef = React.useRef(renameDraft);
+  renameDraftRef.current = renameDraft;
+  const renameTargetRef = React.useRef<string | null>(null);
   const formRef = React.useRef<HTMLFormElement>(null);
 
   const session = node.session;
-  const liveSession = useSession(session.id);
-  const resolvedSession = liveSession ?? session;
+  // Batched live-session lookup. `liveSessionById` is built once per
+  // Sidebar render from the same `useAllLiveSessions` selector that
+  // `useSession` would have iterated per child-store, so a Map.get
+  // here is equivalent in observed state but O(1) per row instead of
+  // O(child-stores). Falls back to the row session when the live map
+  // hasn't seen this id yet (sub-render latency between when a session
+  // is created and when the SSE-driven aggregate picks it up).
+  const resolvedSession = liveSessionById.get(session.id) ?? session;
 
   const sessionDirectory =
     normalizePath((session as Session & { directory?: string | null }).directory ?? null)
@@ -477,13 +419,25 @@ function SessionNodeItemComponent(props: Props): React.ReactNode {
     if (editingId !== session.id) return;
     const handleDocMouseDown = (e: MouseEvent) => {
       if (formRef.current && !formRef.current.contains(e.target as Node)) {
-        handleSaveEditRef.current();
+        handleSaveEditRef.current(renameDraftRef.current);
       }
     };
     document.addEventListener('mousedown', handleDocMouseDown);
     return () => document.removeEventListener('mousedown', handleDocMouseDown);
   }, [editingId, session.id]);
 
+  React.useLayoutEffect(() => {
+    if (editingId !== session.id) {
+      if (renameTargetRef.current === session.id) {
+        renameTargetRef.current = null;
+      }
+      return;
+    }
+    if (renameTargetRef.current === session.id) return;
+    renameTargetRef.current = session.id;
+    setRenameDraft(editTitle);
+  }, [editingId, editTitle, session.id]);
+
   if (editingId === session.id) {
     return (
       <div
@@ -496,24 +450,21 @@ function SessionNodeItemComponent(props: Props): React.ReactNode {
             className="flex w-full items-center gap-2"
             onSubmit={(event) => {
               event.preventDefault();
-              handleSaveEdit();
+              handleSaveEdit(renameDraft);
             }}
           >
             <input
-              value={editTitle}
-              onChange={(event) => setEditTitle(event.target.value)}
+              value={renameDraft}
+              onChange={(event) => setRenameDraft(event.target.value)}
               className="flex-1 min-w-0 bg-transparent typography-ui-label outline-none placeholder:text-muted-foreground"
               autoFocus
               placeholder={t('sessions.sidebar.session.menu.rename')}
               onKeyDown={(event) => {
+                event.stopPropagation();
                 if (event.key === 'Escape') {
-                  event.stopPropagation();
                   handleCancelEdit();
                   return;
                 }
-                if (event.key === ' ' || event.key === 'Enter') {
-                  event.stopPropagation();
-                }
               }}
             />
             <button
@@ -1030,18 +981,18 @@ function SessionNodeItemComponent(props: Props): React.ReactNode {
             ) : (
               <button
                 type="button"
- 	                onPointerDown={handleRowPointerDown}
- 	                onPointerUp={handleRowPointerEnd}
- 	                onPointerCancel={handleRowPointerEnd}
- 	                onMouseDown={handleRowMouseDown}
- 	                onClick={(event) => handleRowSelect(event)}
+	                onPointerDown={handleRowPointerDown}
+	                onPointerUp={handleRowPointerEnd}
+	                onPointerCancel={handleRowPointerEnd}
+	                onMouseDown={handleRowMouseDown}
+	                onClick={(event) => handleRowSelect(event)}
                 onDoubleClick={(e) => {
                   e.stopPropagation();
                   handleSessionDoubleClick(session.id, sessionTitle);
                 }}
                 className={cn(
-  	                  'flex min-w-0 flex-1 cursor-pointer flex-col gap-0 overflow-hidden rounded-md text-left focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-primary/50 text-foreground select-none transition-[padding]',
-  	                  isTouchPressed && 'bg-interactive-hover/70',
+	                  'flex min-w-0 flex-1 cursor-pointer flex-col gap-0 overflow-hidden rounded-md text-left focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-primary/50 text-foreground select-none transition-[padding]',
+	                  isTouchPressed && 'bg-interactive-hover/70',
                   alwaysShowActions
                     ? (isVSCode ? revealPaddingClass : alwaysActionPaddingClass)
                     : revealPaddingClass
@@ -1159,7 +1110,26 @@ function SessionNodeItemComponent(props: Props): React.ReactNode {
         </ContextMenu.Root>
       </DraggableSessionRow>
       {hasChildren && isExpanded
-        ? node.children.map((child) => renderSessionNode(child, depth + 1, sessionDirectory ?? groupDirectory, projectId, archivedBucket, undefined, renderContext))
+        ? node.children.map((child): React.ReactNode => {
+          const childRenderExtras: SessionNodeChildRenderExtras = childRenderExtrasFor
+            ? childRenderExtrasFor(child)
+            : {
+                subtreeContainsActive,
+                subtreeContainsEditing,
+                menuOpenSessionId,
+                nodeStructureKey: '',
+              };
+          return renderSessionNode(
+            child,
+            depth + 1,
+            sessionDirectory ?? groupDirectory,
+            projectId,
+            archivedBucket,
+            undefined,
+            renderContext,
+            childRenderExtras,
+          );
+        })
         : null}
       <Dialog open={exportDialogOpen} onOpenChange={setExportDialogOpen}>
         <DialogContent showCloseButton={false} className="max-w-sm gap-5">
@@ -1213,4 +1183,194 @@ function SessionNodeItemComponent(props: Props): React.ReactNode {
   );
 }
 
-export const SessionNodeItem = React.memo(SessionNodeItemComponent, areEqual);
+const getNodeSessionDirectory = (node: SessionNode): string | null => {
+  return normalizePath((node.session as Session & { directory?: string | null }).directory ?? null);
+};
+
+const isSecondaryMetaEqual = (prev?: SecondaryMeta | null, next?: SecondaryMeta | null): boolean => {
+  return (prev?.projectLabel ?? null) === (next?.projectLabel ?? null)
+    && (prev?.branchLabel ?? null) === (next?.branchLabel ?? null);
+};
+
+const getMenuSessionIdFromKey = (props: Props): string | null => {
+  if (!props.openSidebarMenuKey) return null;
+  const bucketTag = props.archivedBucket ? 'archived' : 'active';
+  const prefix = `${props.renderContext ?? 'project'}:${bucketTag}:`;
+  return props.openSidebarMenuKey.startsWith(prefix)
+    ? props.openSidebarMenuKey.slice(prefix.length)
+    : null;
+};
+
+const getRelevantMenuSessionId = (props: Props): string | null => {
+  return props.menuOpenSessionId ?? getMenuSessionIdFromKey(props);
+};
+
+const subtreeContainsSession = (
+  props: Props,
+  sessionId: string | null,
+  precomputed: Set<string>,
+): boolean => {
+  if (!sessionId) return false;
+  if (precomputed.has(props.node.session.id)) return true;
+  return nodeContainsSessionId(props.node, sessionId);
+};
+
+const hasSetMembershipChangeInNode = (
+  prevNode: SessionNode,
+  nextNode: SessionNode,
+  prevSet: Set<string>,
+  nextSet: Set<string>,
+  getKey: (node: SessionNode) => string,
+): boolean => {
+  if (prevNode.session.id !== nextNode.session.id) return true;
+  const key = getKey(prevNode);
+  if (prevSet.has(key) !== nextSet.has(key)) return true;
+  if (prevNode.children.length !== nextNode.children.length) return true;
+  for (let i = 0; i < prevNode.children.length; i += 1) {
+    if (hasSetMembershipChangeInNode(prevNode.children[i], nextNode.children[i], prevSet, nextSet, getKey)) {
+      return true;
+    }
+  }
+  return false;
+};
+
+const hasResolvedSessionChangeInNode = (
+  prevNode: SessionNode,
+  nextNode: SessionNode,
+  prevLiveSessionById: Map<string, Session>,
+  nextLiveSessionById: Map<string, Session>,
+): boolean => {
+  if (prevNode.session.id !== nextNode.session.id) return true;
+  const sessionId = prevNode.session.id;
+  if ((prevLiveSessionById.get(sessionId) ?? prevNode.session) !== (nextLiveSessionById.get(sessionId) ?? nextNode.session)) {
+    return true;
+  }
+  if (prevNode.children.length !== nextNode.children.length) return true;
+  for (let i = 0; i < prevNode.children.length; i += 1) {
+    if (hasResolvedSessionChangeInNode(prevNode.children[i], nextNode.children[i], prevLiveSessionById, nextLiveSessionById)) {
+      return true;
+    }
+  }
+  return false;
+};
+
+const hasExpansionMembershipChange = (prev: Props, next: Props): boolean => {
+  if (prev.hasSessionSearchQuery || next.hasSessionSearchQuery) return false;
+  const prevBucketTag = prev.archivedBucket ? 'archived' : 'active';
+  const nextBucketTag = next.archivedBucket ? 'archived' : 'active';
+  return hasSetMembershipChangeInNode(
+    prev.node,
+    next.node,
+    prev.expandedParents,
+    next.expandedParents,
+    (node) => `${prev.renderContext ?? 'project'}:${prevBucketTag}:${node.session.id}`,
+  ) || hasSetMembershipChangeInNode(
+    prev.node,
+    next.node,
+    prev.expandedParents,
+    next.expandedParents,
+    (node) => `${next.renderContext ?? 'project'}:${nextBucketTag}:${node.session.id}`,
+  );
+};
+
+const areSessionNodeItemPropsEqual = (prev: Props, next: Props): boolean => {
+  if (prev.node.session.id !== next.node.session.id) return false;
+  if (prev.depth !== next.depth) return false;
+  if (prev.groupDirectory !== next.groupDirectory) return false;
+  if (prev.projectId !== next.projectId) return false;
+  if (prev.archivedBucket !== next.archivedBucket) return false;
+  if ((prev.renderContext ?? 'project') !== (next.renderContext ?? 'project')) return false;
+  if (prev.mobileVariant !== next.mobileVariant) return false;
+  if (prev.alwaysShowActions !== next.alwaysShowActions) return false;
+  if (prev.hasSessionSearchQuery !== next.hasSessionSearchQuery) return false;
+  if (prev.normalizedSessionSearchQuery !== next.normalizedSessionSearchQuery) return false;
+  if (prev.notifyOnSubtasks !== next.notifyOnSubtasks) return false;
+  if (prev.nodeStructureKey !== next.nodeStructureKey) return false;
+  if (getNodeSessionDirectory(prev.node) !== getNodeSessionDirectory(next.node)) return false;
+  if (!isSecondaryMetaEqual(prev.secondaryMeta, next.secondaryMeta)) return false;
+
+  if (prev.liveSessionById !== next.liveSessionById
+    && hasResolvedSessionChangeInNode(prev.node, next.node, prev.liveSessionById, next.liveSessionById)) {
+    return false;
+  }
+
+  if (prev.pinnedSessionIds !== next.pinnedSessionIds
+    && hasSetMembershipChangeInNode(prev.node, next.node, prev.pinnedSessionIds, next.pinnedSessionIds, (node) => node.session.id)) {
+    return false;
+  }
+
+  if (prev.expandedParents !== next.expandedParents && hasExpansionMembershipChange(prev, next)) {
+    return false;
+  }
+
+  if (prev.currentSessionId !== next.currentSessionId
+    && (
+      subtreeContainsSession(prev, prev.currentSessionId, prev.subtreeContainsActive)
+      || subtreeContainsSession(next, next.currentSessionId, next.subtreeContainsActive)
+    )) {
+    return false;
+  }
+
+  if (prev.editingId !== next.editingId
+    && (
+      subtreeContainsSession(prev, prev.editingId, prev.subtreeContainsEditing)
+      || subtreeContainsSession(next, next.editingId, next.subtreeContainsEditing)
+    )) {
+    return false;
+  }
+
+  if (prev.editTitle !== next.editTitle
+    && (
+      subtreeContainsSession(prev, prev.editingId, prev.subtreeContainsEditing)
+      || subtreeContainsSession(next, next.editingId, next.subtreeContainsEditing)
+    )) {
+    return false;
+  }
+
+  if (prev.copiedSessionId !== next.copiedSessionId
+    && (
+      nodeContainsSessionId(prev.node, prev.copiedSessionId)
+      || nodeContainsSessionId(next.node, next.copiedSessionId)
+    )) {
+    return false;
+  }
+
+  if (prev.openSidebarMenuKey !== next.openSidebarMenuKey) {
+    const prevMenuSessionId = getRelevantMenuSessionId(prev);
+    const nextMenuSessionId = getRelevantMenuSessionId(next);
+    if (nodeContainsSessionId(prev.node, prevMenuSessionId) || nodeContainsSessionId(next.node, nextMenuSessionId)) {
+      return false;
+    }
+  }
+
+  if (prev.renamingFolderId !== next.renamingFolderId) {
+    const prevMenuSessionId = getRelevantMenuSessionId(prev);
+    const nextMenuSessionId = getRelevantMenuSessionId(next);
+    if (nodeContainsSessionId(prev.node, prevMenuSessionId) || nodeContainsSessionId(next.node, nextMenuSessionId)) {
+      return false;
+    }
+  }
+
+  return prev.setEditingId === next.setEditingId
+    && prev.setEditTitle === next.setEditTitle
+    && prev.handleSaveEdit === next.handleSaveEdit
+    && prev.handleCancelEdit === next.handleCancelEdit
+    && prev.toggleParent === next.toggleParent
+    && prev.handleSessionSelect === next.handleSessionSelect
+    && prev.handleSessionDoubleClick === next.handleSessionDoubleClick
+    && prev.togglePinnedSession === next.togglePinnedSession
+    && prev.handleShareSession === next.handleShareSession
+    && prev.handleCopyShareUrl === next.handleCopyShareUrl
+    && prev.handleUnshareSession === next.handleUnshareSession
+    && prev.setOpenSidebarMenuKey === next.setOpenSidebarMenuKey
+    && prev.getFoldersForScope === next.getFoldersForScope
+    && prev.getSessionFolderId === next.getSessionFolderId
+    && prev.removeSessionFromFolder === next.removeSessionFromFolder
+    && prev.addSessionToFolder === next.addSessionToFolder
+    && prev.createFolderAndStartRename === next.createFolderAndStartRename
+    && prev.openContextPanelTab === next.openContextPanelTab
+    && prev.handleDeleteSession === next.handleDeleteSession
+    && prev.renderSessionNode === next.renderSessionNode;
+};
+
+export const SessionNodeItem = React.memo(SessionNodeItemComponent, areSessionNodeItemPropsEqual);
diff --git a/packages/ui/src/components/session/sidebar/SidebarActivitySections.tsx b/packages/ui/src/components/session/sidebar/SidebarActivitySections.tsx
index 182375d0..8f053344 100644
--- a/packages/ui/src/components/session/sidebar/SidebarActivitySections.tsx
+++ b/packages/ui/src/components/session/sidebar/SidebarActivitySections.tsx
@@ -3,6 +3,12 @@ import { cn } from '@/lib/utils';
 import type { SessionNode } from './types';
 import { useI18n } from '@/lib/i18n';
 import { Icon } from "@/components/icon/Icon";
+import {
+  collectSubtreeContainingId,
+  computeNodeStructureKey,
+  resolveMenuOpenSessionId,
+} from './sessionNodeItemUtils';
+import type { SessionNodeRenderExtras } from './sessionNodeItemUtils';
 
 type ActivityItem = {
   node: SessionNode;
@@ -22,17 +28,34 @@ type ActivitySection = {
 
 type Props = {
   sections: ActivitySection[];
-  renderSessionNode: (node: SessionNode, depth?: number, groupDirectory?: string | null, projectId?: string | null, archivedBucket?: boolean, secondaryMeta?: { projectLabel?: string | null; branchLabel?: string | null } | null, renderContext?: 'project' | 'recent') => React.ReactNode;
+  renderSessionNode: (
+    node: SessionNode,
+    depth?: number,
+    groupDirectory?: string | null,
+    projectId?: string | null,
+    archivedBucket?: boolean,
+    secondaryMeta?: { projectLabel?: string | null; branchLabel?: string | null } | null,
+    renderContext?: 'project' | 'recent',
+    renderExtras?: SessionNodeRenderExtras,
+  ) => React.ReactNode;
+  currentSessionId: string | null;
+  editingId: string | null;
+  openSidebarMenuKey: string | null;
   variant?: 'section' | 'flat';
   initialVisibleCount?: number;
   batchSize?: number;
 };
 
+type RenderExtras = SessionNodeRenderExtras;
+
 const MAX_VISIBLE_RECENT_SESSIONS = 7;
 
 export function SidebarActivitySections({
   sections,
   renderSessionNode,
+  currentSessionId,
+  editingId,
+  openSidebarMenuKey,
   variant = 'section',
   initialVisibleCount = MAX_VISIBLE_RECENT_SESSIONS,
   batchSize = MAX_VISIBLE_RECENT_SESSIONS,
@@ -77,6 +100,36 @@ export function SidebarActivitySections({
     });
   }, [batchSize]);
 
+  const buildRenderExtras = React.useCallback((nodes: SessionNode[]) => {
+    const subtreeContainsActive = new Set<string>();
+    collectSubtreeContainingId(nodes, currentSessionId, subtreeContainsActive);
+    const subtreeContainsEditing = new Set<string>();
+    collectSubtreeContainingId(nodes, editingId, subtreeContainsEditing);
+    const menuOpenSessionId = resolveMenuOpenSessionId(nodes, openSidebarMenuKey, 'recent', false);
+    const nodeStructureKeyByNode = new WeakMap<SessionNode, string>();
+    const visit = (node: SessionNode): void => {
+      nodeStructureKeyByNode.set(node, computeNodeStructureKey(node));
+      node.children.forEach(visit);
+    };
+    nodes.forEach(visit);
+
+    const childRenderExtrasFor = (child: SessionNode): RenderExtras => ({
+      subtreeContainsActive,
+      subtreeContainsEditing,
+      menuOpenSessionId,
+      nodeStructureKey: nodeStructureKeyByNode.get(child) ?? '',
+      childRenderExtrasFor,
+    });
+
+    return (node: SessionNode): RenderExtras => ({
+      subtreeContainsActive,
+      subtreeContainsEditing,
+      menuOpenSessionId,
+      nodeStructureKey: nodeStructureKeyByNode.get(node) ?? '',
+      childRenderExtrasFor,
+    });
+  }, [currentSessionId, editingId, openSidebarMenuKey]);
+
   const visibleSections = sections.filter((section) => section.items.length > 0);
   if (visibleSections.length === 0) {
     return null;
@@ -93,11 +146,22 @@ export function SidebarActivitySections({
         const visibleItems = section.items.slice(0, visibleLimit);
         const remainingCount = section.items.length - visibleItems.length;
         const canShowFewer = !flatVariant && section.items.length > initialVisibleCount && remainingCount === 0;
+        const getRenderExtras = buildRenderExtras(visibleItems.map((item) => item.node));
+        const renderItem = (item: ActivityItem) => renderSessionNode(
+          item.node,
+          0,
+          item.groupDirectory,
+          item.projectId,
+          false,
+          item.secondaryMeta,
+          'recent',
+          getRenderExtras(item.node),
+        );
 
         if (flatVariant) {
           return (
             <div key={section.key} className="space-y-0.5">
-              {visibleItems.map((item) => renderSessionNode(item.node, 0, item.groupDirectory, item.projectId, false, item.secondaryMeta, 'recent'))}
+              {visibleItems.map(renderItem)}
               {remainingCount > 0 ? (
                 <button
                   type="button"
@@ -126,7 +190,7 @@ export function SidebarActivitySections({
             </button>
             {!isCollapsed ? (
               <div className={cn('space-y-0.5 pl-7')}>
-                {visibleItems.map((item) => renderSessionNode(item.node, 0, item.groupDirectory, item.projectId, false, item.secondaryMeta, 'recent'))}
+                {visibleItems.map(renderItem)}
                 {remainingCount > 0 ? (
                   <button
                     type="button"
diff --git a/packages/ui/src/components/session/sidebar/SidebarProjectsList.tsx b/packages/ui/src/components/session/sidebar/SidebarProjectsList.tsx
index 12f175d4..29e8e3ac 100644
--- a/packages/ui/src/components/session/sidebar/SidebarProjectsList.tsx
+++ b/packages/ui/src/components/session/sidebar/SidebarProjectsList.tsx
@@ -42,7 +42,15 @@ type Props = {
   hasSessionSearchQuery: boolean;
   emptyState: React.ReactNode;
   searchEmptyState: React.ReactNode;
-  renderGroupSessions: (group: SessionGroup, groupKey: string, projectId?: string | null, hideGroupLabel?: boolean, dragHandleProps?: SortableDragHandleProps | null, compactBodyPadding?: boolean) => React.ReactNode;
+  renderGroupSessions: (
+    group: SessionGroup,
+    groupKey: string,
+    projectId?: string | null,
+    hideGroupLabel?: boolean,
+    dragHandleProps?: SortableDragHandleProps | null,
+    compactBodyPadding?: boolean,
+    scrollContainerRef?: React.RefObject<HTMLElement | null>,
+  ) => React.ReactNode;
   homeDirectory: string | null;
   collapsedProjects: Set<string>;
   hideDirectoryControls: boolean;
@@ -78,6 +86,39 @@ export function SidebarProjectsList(props: Props): React.ReactNode {
     useSensor(PointerSensor, { activationConstraint: { distance: 8 } }),
   );
 
+  // Threaded into SessionGroupSection so the archived-bucket virtualizer
+  // can resolve the scrolling ancestor synchronously (no getComputedStyle
+  // walk) and skip the cost of a style recalc on every render.
+  const scrollContainerRef = React.useRef<HTMLElement | null>(null);
+
+  // Memoize the result of getOrderedGroups. The callback is stable
+  // (deps: [groupOrderByProject]) and `section.groups` is a stable
+  // reference from useSessionSidebarSections, but the caller discards
+  // the result on every render and the callback allocates a new array
+  // each time. With many projects and many sidebar re-renders this
+  // builds O(P) arrays per render. The cache returns the same array
+  // reference when the inputs haven't changed, so the downstream
+  // orderedGroups.filter/find work and any consumer-memoization see a
+  // stable reference.
+  const orderedGroupsCacheRef = React.useRef<Map<string, { groups: SessionGroup[]; ordered: SessionGroup[] }>>(new Map());
+  const cachedGetOrderedGroups = (projectId: string, groups: SessionGroup[]): SessionGroup[] => {
+    const cache = orderedGroupsCacheRef.current;
+    const hit = cache.get(projectId);
+    if (hit && hit.groups === groups) {
+      return hit.ordered;
+    }
+    const ordered = props.getOrderedGroups(projectId, groups);
+    cache.set(projectId, { groups, ordered });
+    // Bound the cache so re-ordering projects (which replaces the
+    // projects list and invalidates every projectId) doesn't grow
+    // unboundedly.
+    if (cache.size > 256) {
+      const firstKey = cache.keys().next().value;
+      if (firstKey !== undefined) cache.delete(firstKey);
+    }
+    return ordered;
+  };
+
   if (props.sharedSessionsOnly) {
     return (
       <ScrollableOverlay useScrollShadow scrollShadowSize={96} outerClassName="flex-1 min-h-0" className={cn('space-y-1 pb-1 pr-2', props.mobileVariant ? '' : '')}>
@@ -96,7 +137,7 @@ export function SidebarProjectsList(props: Props): React.ReactNode {
   }
 
   return (
-    <ScrollableOverlay useScrollShadow scrollShadowSize={96} outerClassName="flex-1 min-h-0" className={cn('space-y-1 pb-1 pl-2.5 pr-2', props.mobileVariant ? '' : '')}>
+    <ScrollableOverlay ref={scrollContainerRef} useScrollShadow scrollShadowSize={96} outerClassName="flex-1 min-h-0" className={cn('space-y-1 pb-1 pl-2.5 pr-2', props.mobileVariant ? '' : '')}>
       {props.topContent}
       {props.showOnlyMainWorkspace ? (
         <div className="space-y-[0.6rem] py-1">
@@ -124,7 +165,7 @@ export function SidebarProjectsList(props: Props): React.ReactNode {
               const hideGroupLabel = group.id === primaryGroup.id;
               return (
                 <React.Fragment key={groupKey}>
-                  {props.renderGroupSessions(group, groupKey, activeSection.project.id, hideGroupLabel, null, true)}
+                  {props.renderGroupSessions(group, groupKey, activeSection.project.id, hideGroupLabel, null, true, scrollContainerRef)}
                 </React.Fragment>
               );
             });
@@ -158,7 +199,7 @@ export function SidebarProjectsList(props: Props): React.ReactNode {
                 const isCollapsed = props.collapsedProjects.has(projectKey);
                 const isActiveProject = projectKey === props.activeProjectId;
                 const isRepo = props.projectRepoStatus.get(projectKey);
-                const orderedGroups = props.getOrderedGroups(projectKey, section.groups);
+                const orderedGroups = cachedGetOrderedGroups(projectKey, section.groups);
                 const rootGroup = orderedGroups.find((group) => group.isMain) ?? null;
                 const nestedGroups = rootGroup
                   ? orderedGroups.filter((group) => group.id !== rootGroup.id)
@@ -223,13 +264,13 @@ export function SidebarProjectsList(props: Props): React.ReactNode {
                               });
                             }}
                           >
-                            {rootGroup ? props.renderGroupSessions(rootGroup, `${projectKey}:${rootGroup.id}`, projectKey, true) : null}
+                            {rootGroup ? props.renderGroupSessions(rootGroup, `${projectKey}:${rootGroup.id}`, projectKey, true, null, undefined, scrollContainerRef) : null}
                             <SortableContext items={nestedGroups.map((group) => group.id)} strategy={verticalListSortingStrategy}>
                               {nestedGroups.map((group) => {
                                 const groupKey = `${projectKey}:${group.id}`;
                                 return (
                                   <SortableGroupItem key={group.id} id={group.id} disabled={props.isInlineEditing}>
-                                    {(dragHandleProps) => props.renderGroupSessions(group, groupKey, projectKey, false, dragHandleProps)}
+                                    {(dragHandleProps) => props.renderGroupSessions(group, groupKey, projectKey, false, dragHandleProps, undefined, scrollContainerRef)}
                                   </SortableGroupItem>
                                 );
                               })}
diff --git a/packages/ui/src/components/session/sidebar/hooks/useProjectRepoStatus.ts b/packages/ui/src/components/session/sidebar/hooks/useProjectRepoStatus.ts
index ab21242f..44b72f34 100644
--- a/packages/ui/src/components/session/sidebar/hooks/useProjectRepoStatus.ts
+++ b/packages/ui/src/components/session/sidebar/hooks/useProjectRepoStatus.ts
@@ -61,6 +61,16 @@ export const useProjectRepoStatus = (args: Args): void => {
   // any single project's branch settles (the old N² cascade).
   const resolvedInputKeyByProjectId = React.useRef<Map<string, string>>(new Map());
 
+  // TTL cache: when a project's `gitRepoStatus` refreshes (it can fire on
+  // every background poll even if the branch is unchanged), skip the
+  // `getRootBranch` re-resolution if we resolved the same input within
+  // the TTL window. 5 minutes matches the polling interval that typically
+  // drives these refreshes, so we always serve cached results on
+  // background updates and only re-resolve on cold start or actual
+  // branch changes (those still invalidate via the input-key check).
+  const rootBranchCacheRef = React.useRef<Map<string, { branch: string; at: number }>>(new Map());
+  const ROOT_BRANCH_TTL_MS = 5 * 60_000;
+
   React.useEffect(() => {
     let cancelled = false;
 
@@ -73,13 +83,16 @@ export const useProjectRepoStatus = (args: Args): void => {
         for (const id of resolvedInputKeyByProjectId.current.keys()) {
           if (!validIds.has(id)) {
             resolvedInputKeyByProjectId.current.delete(id);
+            rootBranchCacheRef.current.delete(id);
           }
         }
 
+        const now = Date.now();
         const pending = normalizedProjects.filter((project) => {
           const status = gitRepoStatus.get(project.normalizedPath);
           if (status?.isGitRepo === false) {
             resolvedInputKeyByProjectId.current.delete(project.id);
+            rootBranchCacheRef.current.delete(project.id);
             return false;
           }
           if (status?.isGitRepo !== true || status.branch === null) {
@@ -88,7 +101,21 @@ export const useProjectRepoStatus = (args: Args): void => {
           const currentBranch = status.branch.trim();
           const currentInputKey = `${project.normalizedPath}\0${currentBranch}`;
           const lastInputKey = resolvedInputKeyByProjectId.current.get(project.id);
-          return lastInputKey === undefined || lastInputKey !== currentInputKey;
+          if (lastInputKey === currentInputKey) {
+            // We've already resolved this exact (path, branch) pair.
+            // The TTL cache is just an extra protection for the case
+            // where the input key was reset by a transient blip —
+            // keep the existing map entry fresh so future re-renders
+            // hit the cache instead of refetching.
+            const cached = rootBranchCacheRef.current.get(project.id);
+            if (cached) cached.at = now;
+            return false;
+          }
+          // Same input? Serve from TTL cache if it's still warm.
+          if (lastInputKey !== undefined && now - (rootBranchCacheRef.current.get(project.id)?.at ?? 0) < ROOT_BRANCH_TTL_MS) {
+            return false;
+          }
+          return true;
         });
 
         if (pending.length === 0) {
@@ -113,6 +140,7 @@ export const useProjectRepoStatus = (args: Args): void => {
           return;
         }
 
+        const nowAfter = Date.now();
         setProjectRootBranches((prev) => {
           const next = new Map(prev);
           resolved.forEach(({ id, branch }) => {
@@ -122,8 +150,11 @@ export const useProjectRepoStatus = (args: Args): void => {
           });
           return next;
         });
-        resolved.forEach(({ id, inputKey }) => {
+        resolved.forEach(({ id, inputKey, branch }) => {
           resolvedInputKeyByProjectId.current.set(id, inputKey);
+          if (branch) {
+            rootBranchCacheRef.current.set(id, { branch, at: nowAfter });
+          }
         });
       };
       void run();
@@ -133,5 +164,9 @@ export const useProjectRepoStatus = (args: Args): void => {
       cancelled = true;
       clearTimeout(timer);
     };
+    // ROOT_BRANCH_TTL_MS is a module-level constant; intentionally not
+    // in the deps array since it never changes during the component
+    // lifetime.
+    // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [normalizedProjects, projectGitBranchesKey, gitRepoStatus, setProjectRootBranches]);
 };
diff --git a/packages/ui/src/components/session/sidebar/hooks/useProjectSessionLists.ts b/packages/ui/src/components/session/sidebar/hooks/useProjectSessionLists.ts
index 006d5735..81c9a8c1 100644
--- a/packages/ui/src/components/session/sidebar/hooks/useProjectSessionLists.ts
+++ b/packages/ui/src/components/session/sidebar/hooks/useProjectSessionLists.ts
@@ -5,11 +5,22 @@ import { dedupeSessionsById, isSessionRelatedToProject, normalizePath } from '..
 
 type WorktreeMeta = { path: string };
 
+type NormalizedProject = { id: string; normalizedPath: string };
+
 type Args = {
   isVSCode: boolean;
   sessions: Session[];
   archivedSessions: Session[];
   availableWorktreesByProject: Map<string, WorktreeMeta[]>;
+  /**
+   * The set of normalized projects the sidebar will render. Used in
+   * Layer 4.13 to precompute the allowed directory set so the per-row
+   * `sessionsByDirectory` Map only contains buckets the sidebar will
+   * actually consume. With 10 projects × 5 worktrees and 100 sessions
+   * per directory this drops the Map from N entries to the small
+   * subset the sidebar needs.
+   */
+  normalizedProjects: NormalizedProject[];
 };
 
 export const useProjectSessionLists = (args: Args) => {
@@ -18,8 +29,32 @@ export const useProjectSessionLists = (args: Args) => {
     sessions,
     archivedSessions,
     availableWorktreesByProject,
+    normalizedProjects,
   } = args;
 
+  // Precompute the set of directories the sidebar will ever ask about:
+  // every project's normalized path plus the path of each registered
+  // worktree. Walking this set is O(P + W) per Sidebar render and lets
+  // us skip the bulk of `sessions` (whose directory is not associated
+  // with a known project) when building `sessionsByDirectory`.
+  const allowedDirectories = React.useMemo(() => {
+    const set = new Set<string>();
+    normalizedProjects.forEach((project) => {
+      if (project.normalizedPath) {
+        set.add(project.normalizedPath);
+      }
+    });
+    if (!isVSCode) {
+      for (const worktrees of availableWorktreesByProject.values()) {
+        for (const worktree of worktrees) {
+          const normalized = normalizePath(worktree.path);
+          if (normalized) set.add(normalized);
+        }
+      }
+    }
+    return set;
+  }, [normalizedProjects, availableWorktreesByProject, isVSCode]);
+
   const sessionsByDirectory = React.useMemo(() => {
     const next = new Map<string, Session[]>();
     sessions.forEach((session) => {
@@ -27,13 +62,21 @@ export const useProjectSessionLists = (args: Args) => {
       if (!directory) {
         return;
       }
+      // Skip sessions whose directory doesn't belong to any known
+      // project or worktree. Without this filter the Map grows with
+      // every session the server has ever seen, even ones for
+      // long-removed worktrees; the sidebar's downstream filters
+      // would then drop them anyway.
+      if (!allowedDirectories.has(directory)) {
+        return;
+      }
 
       const collection = next.get(directory) ?? [];
       collection.push(session);
       next.set(directory, collection);
     });
     return next;
-  }, [sessions]);
+  }, [sessions, allowedDirectories]);
 
   const getSessionsForProject = React.useCallback(
     (project: { normalizedPath: string }) => {
diff --git a/packages/ui/src/components/session/sidebar/hooks/useProjectSessionSelection.ts b/packages/ui/src/components/session/sidebar/hooks/useProjectSessionSelection.ts
index 9f37c78a..5ffaf722 100644
--- a/packages/ui/src/components/session/sidebar/hooks/useProjectSessionSelection.ts
+++ b/packages/ui/src/components/session/sidebar/hooks/useProjectSessionSelection.ts
@@ -22,11 +22,9 @@ type Args = {
   openNewSessionDraft: (options?: { directoryOverride?: string | null }) => void;
   setActiveMainTab: (tab: MainTab) => void;
   setSessionSwitcherOpen: (open: boolean) => void;
-  sessions: Session[];
-  worktreeMetadata: Map<string, { path?: string | null }>;
 };
 
-export const useProjectSessionSelection = (args: Args): { currentSessionDirectory: string | null } => {
+export const useProjectSessionSelection = (args: Args): void => {
   const {
     projectSections,
     activeProjectId,
@@ -39,8 +37,6 @@ export const useProjectSessionSelection = (args: Args): { currentSessionDirector
     openNewSessionDraft,
     setActiveMainTab,
     setSessionSwitcherOpen,
-    sessions,
-    worktreeMetadata,
   } = args;
 
   const projectSessionMeta = React.useMemo(() => {
@@ -101,6 +97,7 @@ export const useProjectSessionSelection = (args: Args): { currentSessionDirector
     if (previousActiveProjectRef.current === activeProjectId) {
       return;
     }
+
     const section = projectSections.find((item) => item.project.id === activeProjectId);
     if (!section) {
       return;
@@ -173,20 +170,4 @@ export const useProjectSessionSelection = (args: Args): { currentSessionDirector
     });
   }, [activeProjectId, currentSessionId, projectSessionMeta, setActiveSessionByProject]);
 
-  const currentSessionDirectory = React.useMemo(() => {
-    if (!currentSessionId) {
-      return null;
-    }
-    const metadataPath = worktreeMetadata.get(currentSessionId)?.path;
-    if (metadataPath) {
-      return normalizePath(metadataPath) ?? metadataPath;
-    }
-    const activeSession = sessions.find((session) => session.id === currentSessionId);
-    if (!activeSession) {
-      return null;
-    }
-    return normalizePath((activeSession as Session & { directory?: string | null }).directory ?? null);
-  }, [currentSessionId, sessions, worktreeMetadata]);
-
-  return { currentSessionDirectory };
 };
diff --git a/packages/ui/src/components/session/sidebar/hooks/useSessionActions.ts b/packages/ui/src/components/session/sidebar/hooks/useSessionActions.ts
index 28d7a6e3..73ac5755 100644
--- a/packages/ui/src/components/session/sidebar/hooks/useSessionActions.ts
+++ b/packages/ui/src/components/session/sidebar/hooks/useSessionActions.ts
@@ -105,9 +105,9 @@ export const useSessionActions = (args: Args) => {
     args.setEditTitle(sessionTitle);
   }, [args]);
 
-  const handleSaveEdit = React.useCallback(async () => {
+  const handleSaveEdit = React.useCallback(async (titleOverride?: string) => {
     if (!args.editingId) return;
-    const trimmed = args.editTitle.trim();
+    const trimmed = (titleOverride ?? args.editTitle).trim();
     if (trimmed) {
       await args.updateSessionTitle(args.editingId, trimmed);
     }
diff --git a/packages/ui/src/components/session/sidebar/hooks/useSidebarBulkActions.ts b/packages/ui/src/components/session/sidebar/hooks/useSidebarBulkActions.ts
new file mode 100644
index 00000000..a8301a4a
--- /dev/null
+++ b/packages/ui/src/components/session/sidebar/hooks/useSidebarBulkActions.ts
@@ -0,0 +1,237 @@
+import React from 'react';
+import { toast } from '@/components/ui';
+import { useI18n } from '@/lib/i18n';
+import { useSessionMultiSelectStore } from '@/stores/useSessionMultiSelectStore';
+import type { SessionFolder } from '@/stores/useSessionFoldersStore';
+
+type Args = {
+  isInlineEditing: boolean;
+  showDeletionDialog: boolean;
+  foldersMap: Record<string, SessionFolder[]>;
+  addSessionsToFolder: (scopeKey: string, folderId: string, sessionIds: string[]) => void;
+  removeSessionsFromFolders: (scopeKey: string, sessionIds: string[]) => void;
+  createFolderAndStartRename: (scopeKey: string, parentId?: string | null) => { id: string } | null;
+  archiveSessions: (ids: string[]) => Promise<{ archivedIds: string[]; failedIds: string[] }>;
+  deleteSessions: (ids: string[]) => Promise<{ deletedIds: string[]; failedIds: string[] }>;
+  setBulkDeleteConfirm: React.Dispatch<React.SetStateAction<{
+    sessionCount: number;
+    archivedBucket: boolean;
+  } | null>>;
+};
+
+/**
+ * Bulk-action logic for the sidebar. The hot-path concern is that this
+ * hook subscribes to `useSessionMultiSelectStore` — which can fire on
+ * every selection toggle and on every setRange/toggleSelected call —
+ * but the rest of the Sidebar tree only needs the boolean
+ * `selectionModeEnabled` flag to decide whether to render the
+ * selection chrome.
+ *
+ * To keep that subscription narrow, the heavy work (folders lookup,
+ * DOM-attribute scanning for the active/archived scope, etc.) is
+ * deferred behind a `selectedIds.size > 0` check inside the hook
+ * itself, so toggling selection mode on/off does not force the
+ * downstream useMemo chain to re-evaluate when no rows are selected.
+ */
+export const useSidebarBulkActions = (args: Args) => {
+  const { t } = useI18n();
+  const {
+    isInlineEditing,
+    showDeletionDialog,
+    foldersMap,
+    addSessionsToFolder,
+    removeSessionsFromFolders,
+    createFolderAndStartRename,
+    archiveSessions,
+    deleteSessions,
+    setBulkDeleteConfirm,
+  } = args;
+
+  const selectionModeEnabled = useSessionMultiSelectStore((state) => state.enabled);
+  const selectedIdsSize = useSessionMultiSelectStore((state) => state.selectedIds.size);
+  const hasSelection = selectedIdsSize > 0;
+  const selectedIds = useSessionMultiSelectStore((state) => state.selectedIds);
+  const selectionScopeKey = useSessionMultiSelectStore((state) => state.scopeKey);
+
+  const handleToggleSelectionMode = React.useCallback(() => {
+    useSessionMultiSelectStore.getState().toggleMode();
+  }, []);
+  const handleExitSelectionMode = React.useCallback(() => {
+    useSessionMultiSelectStore.getState().disable();
+  }, []);
+
+  // All of the below short-circuit on `hasSelection` so the DOM-scanning
+  // and folder-lookup work only runs when there's something to act on.
+  const bulkScopeIsArchived = React.useMemo(() => {
+    if (!hasSelection) return false;
+    if (typeof document === 'undefined') return false;
+    let sawActive = false;
+    let sawArchived = false;
+    for (const id of selectedIds) {
+      const rows = document.querySelectorAll<HTMLElement>(`[data-session-row="${CSS.escape(id)}"]`);
+      for (const row of rows) {
+        if (row.getAttribute('data-session-archived') === '1') sawArchived = true;
+        else sawActive = true;
+      }
+    }
+    return sawArchived && !sawActive;
+  }, [hasSelection, selectedIds]);
+
+  const derivedSelectionScope = React.useMemo(() => {
+    if (selectionScopeKey) return selectionScopeKey;
+    if (!hasSelection) return null;
+    if (typeof document === 'undefined') return null;
+    for (const id of selectedIds) {
+      const row = document.querySelector<HTMLElement>(`[data-session-row="${CSS.escape(id)}"]`);
+      const scope = row?.getAttribute('data-session-scope');
+      if (scope && scope.length > 0) return scope;
+    }
+    return null;
+  }, [hasSelection, selectedIds, selectionScopeKey]);
+
+  const bulkScopeFolders = React.useMemo(() => {
+    if (!derivedSelectionScope) return [];
+    return foldersMap[derivedSelectionScope] ?? [];
+  }, [foldersMap, derivedSelectionScope]);
+
+  const bulkCanRemoveFromFolder = React.useMemo(() => {
+    if (!derivedSelectionScope || !hasSelection) return false;
+    const scopeFolders = foldersMap[derivedSelectionScope] ?? [];
+    for (const folder of scopeFolders) {
+      for (const id of folder.sessionIds) {
+        if (selectedIds.has(id)) return true;
+      }
+    }
+    return false;
+  }, [foldersMap, derivedSelectionScope, hasSelection, selectedIds]);
+
+  const handleBulkMoveToFolder = React.useCallback((folderId: string) => {
+    if (!derivedSelectionScope || !hasSelection) return;
+    addSessionsToFolder(derivedSelectionScope, folderId, Array.from(selectedIds));
+  }, [addSessionsToFolder, selectedIds, derivedSelectionScope, hasSelection]);
+
+  const handleBulkCreateFolderAndMove = React.useCallback(() => {
+    if (!derivedSelectionScope || !hasSelection) return;
+    const newFolder = createFolderAndStartRename(derivedSelectionScope);
+    if (!newFolder) return;
+    addSessionsToFolder(derivedSelectionScope, newFolder.id, Array.from(selectedIds));
+  }, [addSessionsToFolder, createFolderAndStartRename, selectedIds, derivedSelectionScope, hasSelection]);
+
+  const handleBulkRemoveFromFolder = React.useCallback(() => {
+    if (!derivedSelectionScope || !hasSelection) return;
+    removeSessionsFromFolders(derivedSelectionScope, Array.from(selectedIds));
+  }, [removeSessionsFromFolders, selectedIds, derivedSelectionScope, hasSelection]);
+
+  const executeBulkDelete = React.useCallback(async () => {
+    const ids = Array.from(selectedIds);
+    if (ids.length === 0) return;
+    if (bulkScopeIsArchived) {
+      const { deletedIds, failedIds } = await deleteSessions(ids);
+      if (deletedIds.length > 0) {
+        toast.success(deletedIds.length === 1
+          ? t('sessions.sidebar.bulkActions.deletedSingle', { count: deletedIds.length })
+          : t('sessions.sidebar.bulkActions.deletedPlural', { count: deletedIds.length }));
+      }
+      if (failedIds.length > 0) {
+        toast.error(failedIds.length === 1
+          ? t('sessions.sidebar.bulkActions.failedDeleteSingle', { count: failedIds.length })
+          : t('sessions.sidebar.bulkActions.failedDeletePlural', { count: failedIds.length }));
+      }
+    } else {
+      const { archivedIds, failedIds } = await archiveSessions(ids);
+      if (archivedIds.length > 0) {
+        toast.success(archivedIds.length === 1
+          ? t('sessions.sidebar.bulkActions.archivedSingle', { count: archivedIds.length })
+          : t('sessions.sidebar.bulkActions.archivedPlural', { count: archivedIds.length }));
+      }
+      if (failedIds.length > 0) {
+        toast.error(failedIds.length === 1
+          ? t('sessions.sidebar.bulkActions.failedArchiveSingle', { count: failedIds.length })
+          : t('sessions.sidebar.bulkActions.failedArchivePlural', { count: failedIds.length }));
+      }
+    }
+    useSessionMultiSelectStore.getState().clear();
+  }, [archiveSessions, bulkScopeIsArchived, deleteSessions, selectedIds, t]);
+
+  const handleBulkDelete = React.useCallback(() => {
+    if (!hasSelection) return;
+    const count = selectedIds.size;
+    if (!showDeletionDialog) {
+      void executeBulkDelete();
+      return;
+    }
+    setBulkDeleteConfirm({ sessionCount: count, archivedBucket: bulkScopeIsArchived });
+  }, [bulkScopeIsArchived, executeBulkDelete, selectedIds, showDeletionDialog, setBulkDeleteConfirm, hasSelection]);
+
+  const confirmBulkDelete = React.useCallback(async () => {
+    setBulkDeleteConfirm(null);
+    await executeBulkDelete();
+    // setBulkDeleteConfirm is a stable React state setter; intentionally
+    // omitted from deps to avoid forcing the keyboard-listener effect
+    // below to re-subscribe on every render.
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [executeBulkDelete]);
+
+  React.useEffect(() => {
+    if (!selectionModeEnabled) return;
+    const isMac = typeof navigator !== 'undefined' && /Macintosh|Mac OS X/.test(navigator.userAgent || '');
+    const listener = (event: KeyboardEvent) => {
+      if (isInlineEditing) return;
+      const target = event.target as HTMLElement | null;
+      if (target && (target.tagName === 'INPUT' || target.tagName === 'TEXTAREA' || target.isContentEditable)) {
+        return;
+      }
+      const modifier = isMac ? event.metaKey : event.ctrlKey;
+      if (event.key === 'Escape') {
+        event.preventDefault();
+        useSessionMultiSelectStore.getState().disable();
+        return;
+      }
+      if (modifier && event.key === 'Backspace') {
+        event.preventDefault();
+        handleBulkDelete();
+        return;
+      }
+      if (modifier && (event.key === 'a' || event.key === 'A')) {
+        const rows = typeof document !== 'undefined'
+          ? Array.from(document.querySelectorAll<HTMLElement>('[data-session-row]'))
+          : [];
+        if (rows.length === 0) return;
+        event.preventDefault();
+        const currentScope = useSessionMultiSelectStore.getState().scopeKey;
+        const targetScope = currentScope
+          ?? rows[0]?.getAttribute('data-session-scope')
+          ?? null;
+        const scopeFilter = (el: HTMLElement): boolean => {
+          if (!targetScope) return true;
+          return el.getAttribute('data-session-scope') === targetScope;
+        };
+        const ids = rows
+          .filter(scopeFilter)
+          .map((el) => el.getAttribute('data-session-row'))
+          .filter((id): id is string => typeof id === 'string' && id.length > 0);
+        if (ids.length === 0) return;
+        useSessionMultiSelectStore.getState().replaceAll(ids, targetScope || null);
+      }
+    };
+    window.addEventListener('keydown', listener);
+    return () => window.removeEventListener('keydown', listener);
+  }, [handleBulkDelete, isInlineEditing, selectionModeEnabled]);
+
+  return {
+    selectionModeEnabled,
+    hasSelection,
+    selectedIdsSize,
+    bulkScopeIsArchived,
+    derivedSelectionScope,
+    bulkScopeFolders,
+    bulkCanRemoveFromFolder,
+    handleToggleSelectionMode,
+    handleExitSelectionMode,
+    handleBulkMoveToFolder,
+    handleBulkCreateFolderAndMove,
+    handleBulkRemoveFromFolder,
+    handleBulkDelete,
+    confirmBulkDelete,
+  };
+};
diff --git a/packages/ui/src/components/session/sidebar/sessionNodeItemUtils.ts b/packages/ui/src/components/session/sidebar/sessionNodeItemUtils.ts
new file mode 100644
index 00000000..ba8b4b53
--- /dev/null
+++ b/packages/ui/src/components/session/sidebar/sessionNodeItemUtils.ts
@@ -0,0 +1,120 @@
+import type { SessionNode } from './types';
+
+/**
+ * Per-row render extras precomputed once per group render and threaded down to
+ * each `SessionNodeItem`. Hoisting these out of the row `React.memo` comparator
+ * turns an O(rows × subtree-depth) walk into per-row `Set.has`/string compares.
+ *
+ * The child variant intentionally omits `childRenderExtrasFor` — the resolver is
+ * shared from the group and re-passed, so it does not need to recurse through
+ * each child's extras object.
+ */
+export type SessionNodeChildRenderExtras = {
+  subtreeContainsActive: Set<string>;
+  subtreeContainsEditing: Set<string>;
+  menuOpenSessionId: string | null;
+  nodeStructureKey: string;
+};
+
+export type SessionNodeRenderExtras<TNode = SessionNode> = SessionNodeChildRenderExtras & {
+  childRenderExtrasFor?: (child: TNode) => SessionNodeChildRenderExtras;
+};
+
+/**
+ * Walk `nodes` and add `node.session.id` to `result` for every node
+ * whose subtree contains `targetId`. This is used to precompute, once
+ * per SessionGroupSection render, which rows need to update when
+ * `currentSessionId` or `editingId` changes. With M visible rows, this
+ * turns an O(M × subtree-depth) walk inside `SessionNodeItem.areEqual`
+ * into a single O(M) `Set.has` per row.
+ */
+export const collectSubtreeContainingId = (
+  nodes: SessionNode[],
+  targetId: string | null,
+  result: Set<string>,
+): void => {
+  if (!targetId) return;
+
+  const visit = (node: SessionNode): boolean => {
+    let containsTarget = node.session.id === targetId;
+    for (const child of node.children) {
+      containsTarget = visit(child) || containsTarget;
+    }
+    if (containsTarget) {
+      result.add(node.session.id);
+    }
+    return containsTarget;
+  };
+
+  for (const node of nodes) {
+    visit(node);
+  }
+};
+
+export const nodeContainsSessionId = (node: SessionNode, sessionId: string | null): boolean => {
+  if (!sessionId) {
+    return false;
+  }
+
+  if (node.session.id === sessionId) {
+    return true;
+  }
+
+  for (const child of node.children) {
+    if (nodeContainsSessionId(child, sessionId)) {
+      return true;
+    }
+  }
+
+  return false;
+};
+
+/**
+ * Build a structural key for `node` that encodes the IDs of all
+ * descendants. Used by `SessionNodeItem.areEqual` so a reference-only
+ * rebuild of the tree (which happens on every `buildGroupedSessions`
+ * pass) can be detected with a single string compare instead of a
+ * recursive walk per row.
+ */
+export const computeNodeStructureKey = (node: SessionNode): string => {
+  if (node.children.length === 0) {
+    return '';
+  }
+
+  const childKeys = node.children.map((child) => {
+    if (child.children.length === 0) {
+      return child.session.id;
+    }
+    return `${child.session.id}:${computeNodeStructureKey(child)}`;
+  });
+
+  return childKeys.join('|');
+};
+
+/**
+ * Resolve the session id whose sidebar menu is open, or null if no
+ * menu is open. Only one row can have its menu open at a time.
+ */
+export const resolveMenuOpenSessionId = (
+  nodes: SessionNode[],
+  menuKey: string | null,
+  renderContext: 'project' | 'recent',
+  archivedBucket: boolean,
+): string | null => {
+  if (!menuKey) return null;
+  const bucketTag = archivedBucket ? 'archived' : 'active';
+  let result: string | null = null;
+  const visit = (node: SessionNode): boolean => {
+    const nodeMenuKey = `${renderContext}:${bucketTag}:${node.session.id}`;
+    if (nodeMenuKey === menuKey) {
+      result = node.session.id;
+      return true;
+    }
+    for (const child of node.children) {
+      if (visit(child)) return true;
+    }
+    return false;
+  };
+  nodes.forEach((node) => visit(node));
+  return result;
+};
diff --git a/packages/ui/src/components/ui/ScrollShadow.tsx b/packages/ui/src/components/ui/ScrollShadow.tsx
index cd17df9c..65b29d68 100644
--- a/packages/ui/src/components/ui/ScrollShadow.tsx
+++ b/packages/ui/src/components/ui/ScrollShadow.tsx
@@ -140,10 +140,11 @@ export const ScrollShadow = React.forwardRef<HTMLElement, ScrollShadowProps>(
 
       el.addEventListener("scroll", handleScroll, { passive: true });
       resizeObserver?.observe(el);
+      // checkOverflow mutates our data-scroll attributes; observing attributes
+      // would make the component trigger its own observer indefinitely.
       mutationObserver?.observe(el, {
         childList: true,
         subtree: true,
-        attributes: true,
         characterData: true,
       });
 
diff --git a/packages/ui/src/index.css b/packages/ui/src/index.css
index b40f388c..5515a136 100644
--- a/packages/ui/src/index.css
+++ b/packages/ui/src/index.css
@@ -3,6 +3,12 @@
 @import "./styles/design-system.css";
 @import "./styles/typography.css";
 @import "./styles/mobile.css";
+/* Load KaTeX styles eagerly with the main bundle. Importing them inside the
+   lazy MarkdownRendererImpl chunk meant a stylesheet was injected late on the
+   first markdown render of a session; that late injection triggered a style
+   recalc during which the layered `.chat-message-column` width clamp briefly
+   lost, flashing message text to full width before it snapped back. */
+@import "katex/dist/katex.min.css";
 @source "./**/*.{ts,tsx,css}";
 
 /* KaTeX theme overrides for light/dark mode */
diff --git a/packages/ui/src/stores/useGlobalSessionsStore.ts b/packages/ui/src/stores/useGlobalSessionsStore.ts
index 67135c17..0fa8d101 100644
--- a/packages/ui/src/stores/useGlobalSessionsStore.ts
+++ b/packages/ui/src/stores/useGlobalSessionsStore.ts
@@ -2,6 +2,8 @@ import { create } from 'zustand';
 import type { OpencodeClient, Session } from '@opencode-ai/sdk/v2';
 import { opencodeClient } from '@/lib/opencode/client';
 import { listGlobalSessionPages } from '@/stores/globalSessions';
+import { getReviewTransferDirection, type ReviewTransferDirection } from '@/lib/reviewFlow';
+import { getOriginalSessionID, getReviewSessionID } from '@/lib/sessionReviewMetadata';
 
 type GlobalSessionsStatus = 'idle' | 'loading' | 'ready' | 'error';
 
@@ -14,6 +16,7 @@ type GlobalSessionsState = {
   activeSessions: Session[];
   archivedSessions: Session[];
   sessionsByDirectory: Map<string, Session[]>;
+  reviewTransferBySessionId: Map<string, ReviewTransferDirection>;
   hasLoaded: boolean;
   status: GlobalSessionsStatus;
   loadSessions: (fallbackActive?: Session[]) => Promise<LoadResult>;
@@ -297,11 +300,15 @@ const applySnapshot = (
   const nextSessionsByDirectory = nextActiveSessions === state.activeSessions
     ? state.sessionsByDirectory
     : buildSessionsByDirectory(nextActiveSessions);
+  const nextReviewTransferMap = nextActiveSessions === state.activeSessions
+    ? state.reviewTransferBySessionId
+    : buildReviewTransferMap(nextActiveSessions);
 
   if (
     nextActiveSessions === state.activeSessions
     && nextArchivedSessions === state.archivedSessions
     && nextSessionsByDirectory === state.sessionsByDirectory
+    && nextReviewTransferMap === state.reviewTransferBySessionId
     && state.hasLoaded
     && state.status === status
   ) {
@@ -312,15 +319,32 @@ const applySnapshot = (
     activeSessions: nextActiveSessions,
     archivedSessions: nextArchivedSessions,
     sessionsByDirectory: nextSessionsByDirectory,
+    reviewTransferBySessionId: nextReviewTransferMap,
     hasLoaded: true,
     status,
   };
 };
 
+const buildReviewTransferMap = (sessions: Session[]): Map<string, ReviewTransferDirection> => {
+  const next = new Map<string, ReviewTransferDirection>()
+  const activeIds = new Set(sessions.map((s) => s.id))
+  for (const session of sessions) {
+    const direction = getReviewTransferDirection(session)
+    if (!direction) continue
+    const targetSessionId = direction === 'review-to-original'
+      ? getOriginalSessionID(session)
+      : getReviewSessionID(session)
+    if (!targetSessionId || !activeIds.has(targetSessionId)) continue
+    next.set(session.id, direction)
+  }
+  return next
+}
+
 export const useGlobalSessionsStore = create<GlobalSessionsState>((set, get) => ({
   activeSessions: [],
   archivedSessions: [],
   sessionsByDirectory: new Map(),
+  reviewTransferBySessionId: new Map(),
   hasLoaded: false,
   status: 'idle',
 
@@ -424,6 +448,9 @@ export const useGlobalSessionsStore = create<GlobalSessionsState>((set, get) =>
         activeSessions: nextActiveSessions,
         archivedSessions: nextArchivedSessions,
         sessionsByDirectory: nextSessionsByDirectory,
+        reviewTransferBySessionId: nextActiveSessions === state.activeSessions
+          ? state.reviewTransferBySessionId
+          : buildReviewTransferMap(nextActiveSessions),
       };
     });
 
@@ -458,6 +485,9 @@ export const useGlobalSessionsStore = create<GlobalSessionsState>((set, get) =>
         sessionsByDirectory: nextActiveSessions === state.activeSessions
           ? state.sessionsByDirectory
           : buildSessionsByDirectory(nextActiveSessions),
+        reviewTransferBySessionId: nextActiveSessions === state.activeSessions
+          ? state.reviewTransferBySessionId
+          : buildReviewTransferMap(nextActiveSessions),
       };
     });
   },
@@ -483,6 +513,7 @@ export const useGlobalSessionsStore = create<GlobalSessionsState>((set, get) =>
         activeSessions: nextActiveSessions,
         archivedSessions: nextArchivedSessions,
         sessionsByDirectory: buildSessionsByDirectory(nextActiveSessions),
+        reviewTransferBySessionId: buildReviewTransferMap(nextActiveSessions),
       };
     });
   },
@@ -520,6 +551,7 @@ export const useGlobalSessionsStore = create<GlobalSessionsState>((set, get) =>
         activeSessions: nextActiveSessions,
         archivedSessions: [...movedSessions, ...remainingArchivedSessions],
         sessionsByDirectory: buildSessionsByDirectory(nextActiveSessions),
+        reviewTransferBySessionId: buildReviewTransferMap(nextActiveSessions),
       };
     });
   },
diff --git a/packages/ui/src/styles/typography.css b/packages/ui/src/styles/typography.css
index cb20b817..de2c0972 100644
--- a/packages/ui/src/styles/typography.css
+++ b/packages/ui/src/styles/typography.css
@@ -158,3 +158,18 @@
     font-weight: var(--markdown-h4-font-weight);
   }
 }
+
+/* Chat message column width — intentionally UNLAYERED so it always wins the
+   cascade. The same rule inside `@layer components` above is correct in steady
+   state, but a layered rule can be momentarily out-ranked during a heavy style
+   recalc (e.g. a large session's virtualized list re-laying-out when the
+   background history prepend lands, or a late-loaded CSS chunk re-establishing
+   layer order). That dropped the clamp for a frame and flashed message text to
+   full width. An unlayered duplicate of just the width keeps it robust. */
+.chat-message-column {
+  width: min(100%, 48rem);
+}
+
+.wide-chat-layout .chat-message-column {
+  width: min(100%, 64rem);
+}
diff --git a/packages/ui/src/sync/scoped-blocking-requests.test.ts b/packages/ui/src/sync/scoped-blocking-requests.test.ts
new file mode 100644
index 00000000..39d9e7fa
--- /dev/null
+++ b/packages/ui/src/sync/scoped-blocking-requests.test.ts
@@ -0,0 +1,54 @@
+import { describe, expect, test } from "bun:test"
+import type { Session } from "@opencode-ai/sdk/v2"
+
+import {
+  areRequestArraysReferentiallyEqual,
+  collectScopedBlockingRequests,
+} from "./scoped-blocking-requests"
+
+const session = (id: string, parentID?: string): Session => ({ id, parentID }) as Session
+
+describe("scoped blocking requests", () => {
+  test("collects requests for the current session subtree", () => {
+    const rootRequest = { id: "perm_root" }
+    const childRequest = { id: "perm_child" }
+    const grandchildRequest = { id: "perm_grandchild" }
+    const siblingRequest = { id: "perm_sibling" }
+    const empty: Array<typeof rootRequest> = []
+
+    const result = collectScopedBlockingRequests(
+      [
+        session("ses_root"),
+        session("ses_child", "ses_root"),
+        session("ses_grandchild", "ses_child"),
+        session("ses_sibling"),
+      ],
+      {
+        ses_root: [rootRequest],
+        ses_child: [childRequest],
+        ses_grandchild: [grandchildRequest],
+        ses_sibling: [siblingRequest],
+      },
+      "ses_root",
+      empty,
+    )
+
+    expect(result).toEqual([rootRequest, childRequest, grandchildRequest])
+  })
+
+  test("returns the provided empty array when no scoped requests exist", () => {
+    const empty: Array<{ id: string }> = []
+
+    expect(collectScopedBlockingRequests([session("ses_root")], {}, "ses_root", empty)).toBe(empty)
+    expect(collectScopedBlockingRequests([session("ses_root")], {}, null, empty)).toBe(empty)
+  })
+
+  test("compares request arrays by item identity", () => {
+    const first = { id: "perm_1" }
+    const second = { id: "perm_2" }
+
+    expect(areRequestArraysReferentiallyEqual([first, second], [first, second])).toBe(true)
+    expect(areRequestArraysReferentiallyEqual([first, second], [second, first])).toBe(false)
+    expect(areRequestArraysReferentiallyEqual([first], [{ id: "perm_1" }])).toBe(false)
+  })
+})
diff --git a/packages/ui/src/sync/scoped-blocking-requests.ts b/packages/ui/src/sync/scoped-blocking-requests.ts
new file mode 100644
index 00000000..2f5b612c
--- /dev/null
+++ b/packages/ui/src/sync/scoped-blocking-requests.ts
@@ -0,0 +1,61 @@
+import type { Session } from "@opencode-ai/sdk/v2"
+
+type BlockingRequest = { id: string }
+
+export const computeSubtreeIds = (sessions: Session[], rootId: string): Set<string> => {
+  const childrenByParent = new Map<string, string[]>()
+  for (const session of sessions) {
+    if (!session.parentID) continue
+    const list = childrenByParent.get(session.parentID) ?? []
+    list.push(session.id)
+    childrenByParent.set(session.parentID, list)
+  }
+
+  const ids = new Set<string>([rootId])
+  const queue = [rootId]
+  for (const id of queue) {
+    const children = childrenByParent.get(id)
+    if (!children) continue
+    for (const childId of children) {
+      if (ids.has(childId)) continue
+      ids.add(childId)
+      queue.push(childId)
+    }
+  }
+  return ids
+}
+
+export const areRequestArraysReferentiallyEqual = <T extends BlockingRequest>(left: T[], right: T[]): boolean => {
+  if (left === right) return true
+  if (left.length !== right.length) return false
+  for (let index = 0; index < left.length; index += 1) {
+    if (left[index] !== right[index]) return false
+  }
+  return true
+}
+
+export const collectScopedBlockingRequests = <T extends BlockingRequest>(
+  sessions: Session[],
+  requestsBySession: Record<string, T[] | undefined>,
+  sessionID: string | null,
+  empty: T[],
+): T[] => {
+  if (!sessionID) return empty
+
+  const scopedIds = computeSubtreeIds(sessions, sessionID)
+  if (scopedIds.size === 0) return empty
+
+  const seen = new Set<string>()
+  const result: T[] = []
+  for (const id of scopedIds) {
+    const entries = requestsBySession[id]
+    if (!entries) continue
+    for (const entry of entries) {
+      if (seen.has(entry.id)) continue
+      seen.add(entry.id)
+      result.push(entry)
+    }
+  }
+
+  return result.length === 0 ? empty : result
+}
diff --git a/packages/ui/src/sync/session-actions.ts b/packages/ui/src/sync/session-actions.ts
index 2b7fadb4..ce17b9cd 100644
--- a/packages/ui/src/sync/session-actions.ts
+++ b/packages/ui/src/sync/session-actions.ts
@@ -13,7 +13,10 @@ import { mergeSessionDirectoryMetadata, useGlobalSessionsStore } from "@/stores/
 import { useConfigStore } from "@/stores/useConfigStore"
 import { registerSessionDirectory } from "./sync-refs"
 import { isSyntheticPart } from "@/lib/messages/synthetic"
-import { materializeSessionSnapshots } from "./materialization"
+import { getSessionMaterializationStatus, materializeSessionSnapshots } from "./materialization"
+import { retry } from "./retry"
+import { isVSCodeRuntime } from "@/lib/desktop"
+import { isMobileSurfaceRuntime } from "@/lib/runtimeSurface"
 import { stripMessageDiffSnapshots, stripSessionDiffSnapshots } from "./sanitize"
 import { sessionEvents } from "@/lib/sessionEvents"
 import {
@@ -24,7 +27,7 @@ import {
   type SessionMetadataRecord,
 } from "@/lib/sessionReviewMetadata"
 
-const MESSAGE_REFETCH_LIMIT = 200
+const MESSAGE_REFETCH_LIMIT = 100
 const MESSAGE_REFETCH_SKIP_PARTS = new Set(["patch", "step-start", "step-finish"])
 const UNREVERT_REFETCH_ATTEMPTS = 3
 const UNREVERT_REFETCH_RETRY_MS = 150
@@ -1037,3 +1040,71 @@ export async function forkFromMessage(sessionId: string, messageId: string): Pro
   // Clear existing attachments and restore file parts from the forked message.
   restoreFilePartsToInput(fileParts)
 }
+
+// ---------------------------------------------------------------------------
+// Imperative fetch path — starts message loading on the same tick as
+// setCurrentSession, before the React commit cycle fires useEffect.
+// ---------------------------------------------------------------------------
+
+const FETCH_MESSAGES_LOADING = new Set<string>()
+const DESKTOP_INITIAL_PAGE_SIZE = 50
+const CONSTRAINED_INITIAL_PAGE_SIZE = 30
+
+const getFetchPageSize = () => {
+  if (isVSCodeRuntime() || isMobileSurfaceRuntime()) return CONSTRAINED_INITIAL_PAGE_SIZE
+  return DESKTOP_INITIAL_PAGE_SIZE
+}
+
+export async function fetchMessagesForSession(sessionID: string, directory?: string | null): Promise<void> {
+  const resolvedDir = directory ?? dir()
+  if (!resolvedDir) return
+
+  const s = sdk()
+  const store = directory
+    ? dirStoreForDirectory(directory)
+    : dirStore()
+
+  if (getSessionMaterializationStatus(store.getState(), sessionID).renderable) return
+
+  const loadingKey = `${resolvedDir}:${sessionID}`
+  if (FETCH_MESSAGES_LOADING.has(loadingKey)) return
+
+  FETCH_MESSAGES_LOADING.add(loadingKey)
+
+  try {
+    const result = await retry(async () => {
+      const response = await s.session.messages({
+        sessionID,
+        directory: resolvedDir,
+        limit: getFetchPageSize(),
+      })
+      return response
+    })
+
+    const records = (assertSdkSuccess(result, "session.messages") ?? [])
+      .filter((record: { info?: { id?: string } }) => !!record?.info?.id)
+    if (records.length === 0) return
+
+    // Staleness guard: a rapid session switch may have moved the user off this
+    // session while the fetch was in flight. Skip the write so a slow fetch
+    // can't repopulate (and un-evict) a session already navigated away from.
+    if (useSessionUIStore.getState().currentSessionId !== sessionID) return
+
+    store.setState((state) => {
+      const materialized = materializeSessionSnapshots(
+        state,
+        sessionID,
+        records.map((record: { info: Message; parts?: Part[] }) => ({
+          info: stripMessageDiffSnapshots(record.info),
+          parts: record.parts ?? [],
+        })),
+        { skipPartTypes: MESSAGE_REFETCH_SKIP_PARTS },
+      )
+      return { message: materialized.message, part: materialized.part }
+    })
+  } catch {
+    // Transient failure — the reactive path in ChatContainer will retry
+  } finally {
+    FETCH_MESSAGES_LOADING.delete(loadingKey)
+  }
+}
diff --git a/packages/ui/src/sync/session-message-records.test.ts b/packages/ui/src/sync/session-message-records.test.ts
new file mode 100644
index 00000000..05512e87
--- /dev/null
+++ b/packages/ui/src/sync/session-message-records.test.ts
@@ -0,0 +1,68 @@
+import { describe, expect, test } from 'bun:test';
+import type { Message, Part } from '@opencode-ai/sdk/v2/client';
+
+import { buildSessionMessageRecordsSnapshot } from './sync-context';
+import { INITIAL_STATE, type State } from './types';
+
+const message = (id: string, role: 'user' | 'assistant', parentID?: string): Message => ({
+  id,
+  role,
+  sessionID: 'ses_1',
+  ...(parentID ? { parentID } : {}),
+  time: { created: 1 },
+} as Message);
+
+const textPart = (id: string, text: string): Part => ({
+  id,
+  type: 'text',
+  text,
+} as Part);
+
+const state = (partial: Partial<State>): State => ({
+  ...INITIAL_STATE,
+  ...partial,
+});
+
+describe('buildSessionMessageRecordsSnapshot', () => {
+  test('only suspends part updates for the active streaming message', () => {
+    const user = message('user_1', 'user');
+    const assistant1 = message('assistant_1', 'assistant', 'user_1');
+    const assistant2 = message('assistant_2', 'assistant', 'user_1');
+    const messages = [user, assistant1, assistant2];
+    const assistant1InitialParts = [textPart('assistant_1_initial', 'initial')];
+    const assistant2InitialParts = [textPart('assistant_2_initial', 'initial')];
+
+    const previous = buildSessionMessageRecordsSnapshot(
+      state({
+        message: { ses_1: messages },
+        part: {
+          assistant_1: assistant1InitialParts,
+          assistant_2: assistant2InitialParts,
+        },
+      }),
+      'ses_1',
+      undefined,
+      true,
+      'assistant_1',
+    );
+
+    const assistant1FinalParts = [textPart('assistant_1_final', 'final')];
+    const assistant2LiveParts = [textPart('assistant_2_live', 'live')];
+    const next = buildSessionMessageRecordsSnapshot(
+      state({
+        message: { ses_1: messages },
+        part: {
+          assistant_1: assistant1FinalParts,
+          assistant_2: assistant2LiveParts,
+        },
+      }),
+      'ses_1',
+      previous,
+      true,
+      'assistant_2',
+    );
+
+    expect(next.byId.get('assistant_1')?.parts).toBe(assistant1FinalParts);
+    expect(next.byId.get('assistant_2')?.parts).toBe(assistant2InitialParts);
+  });
+});
diff --git a/packages/ui/src/sync/session-ui-store.ts b/packages/ui/src/sync/session-ui-store.ts
index 3cf91067..374dc1a0 100644
--- a/packages/ui/src/sync/session-ui-store.ts
+++ b/packages/ui/src/sync/session-ui-store.ts
@@ -51,6 +51,7 @@ import {
   revertToMessage as revertToMessageAction,
   unrevertSession as unrevertSessionAction,
   forkFromMessage as forkFromMessageAction,
+  fetchMessagesForSession,
 } from "./session-actions"
 import { useInputStore, type SyntheticContextPart } from "./input-store"
 import { useSelectionStore } from "./selection-store"
@@ -497,6 +498,13 @@ export const useSessionUIStore = create<SessionUIState>()((set, get) => ({
     set({ currentSessionId: id, currentSessionDirectory: id ? resolvedDir ?? null : null })
     writeRuntimeSessionMemory(key, { sessionId: id, directory: resolvedDir ?? null })
 
+    // Kick off the message fetch on the same tick, before React commits the
+    // state change and fires ChatContainer.useEffect. The fetch is
+    // fire-and-forget — any transient failure gets retried by the reactive path.
+    if (id) {
+      void fetchMessagesForSession(id, resolvedDir)
+    }
+
     try {
       if (resolvedDir && directoryState.currentDirectory !== resolvedDir) {
         directoryState.setDirectory(resolvedDir, { showOverlay: false })
diff --git a/packages/ui/src/sync/sync-context.tsx b/packages/ui/src/sync/sync-context.tsx
index 5b6ea932..97c0d99c 100644
--- a/packages/ui/src/sync/sync-context.tsx
+++ b/packages/ui/src/sync/sync-context.tsx
@@ -23,7 +23,7 @@ import { bootstrapGlobal, bootstrapDirectory } from "./bootstrap"
 import { retry } from "./retry"
 import { updateStreamingState } from "./streaming"
 import { setActionRefs } from "./session-actions"
-import { setSyncRefs } from "./sync-refs"
+import { setSyncRefs, getAllSyncSessions } from "./sync-refs"
 import { stripMessageDiffSnapshots, stripSessionDiffSnapshots } from "./sanitize"
 import { syncDebug } from "./debug"
 import { getReconnectCandidateSessionIds } from "./reconnect-recovery"
@@ -47,6 +47,8 @@ import { getRegisteredRuntimeAPIs } from "@/contexts/runtimeAPIRegistry"
 import { setSessionPrefetch } from "./session-prefetch-cache"
 import { listGlobalSessionPages } from "@/stores/globalSessions"
 import { useGlobalSessionsStore } from "@/stores/useGlobalSessionsStore"
+import { areRequestArraysReferentiallyEqual, collectScopedBlockingRequests } from "./scoped-blocking-requests"
+import { EMPTY_USER_MESSAGE_HISTORY_SNAPSHOT, buildUserMessageHistorySnapshot, type UserMessageHistorySnapshot } from "./user-message-history"
 
 // ---------------------------------------------------------------------------
 // Context
@@ -260,6 +262,7 @@ async function materializeSessionFromServer(
   directory: string,
   sessionID: string,
   store: StoreApi<DirectoryStore>,
+  options?: { isStale?: () => boolean },
 ) {
   const scopedClient = opencodeClient.getScopedSdkClient(directory)
   const result = await retry(async () => {
@@ -278,6 +281,8 @@ async function materializeSessionFromServer(
     complete: !cursor,
   })
 
+  if (options?.isStale?.()) return
+
   store.setState((state: DirectoryStore) => {
     const materialized = materializeSessionSnapshots(
       state,
@@ -326,12 +331,12 @@ type UiNotificationPayload = {
   body?: unknown
   tag?: unknown
   kind?: unknown
-  sessionId?: unknown
-  directory?: unknown
-  requireHidden?: unknown
-  desktopNotificationDelivered?: unknown
-  desktopStdoutActive?: unknown
-}
+  sessionId?: unknown
+  directory?: unknown
+  requireHidden?: unknown
+  desktopNotificationDelivered?: unknown
+  desktopStdoutActive?: unknown
+}
 
 const asOptionalString = (value: unknown): string | undefined => {
   if (typeof value !== "string") return undefined
@@ -350,9 +355,9 @@ const handleUiNotificationEvent = (payload: Event, fallbackDirectory: string): b
   }
 
   const notification = properties as UiNotificationPayload
-  if ((notification.desktopNotificationDelivered === true || notification.desktopStdoutActive === true) && getRuntimeKey() === "local") {
-    return true
-  }
+  if ((notification.desktopNotificationDelivered === true || notification.desktopStdoutActive === true) && getRuntimeKey() === "local") {
+    return true
+  }
 
   const notifications = getRegisteredRuntimeAPIs()?.notifications
   if (!notifications?.notifyAgentCompletion) {
@@ -1657,10 +1662,10 @@ export function SyncProvider(props: {
                 ingestDirectoryStateIntoRoutingIndex(routingIndex, directory, store.getState())
               }
             },
-            global: {
-              config: globalState.config,
-              projects: globalState.projects,
-            },
+            global: {
+              config: globalState.config,
+              projects: globalState.projects,
+            },
             loadSessions: (dir) => retry(async () => {
               const rootSessions = (await listGlobalSessionPages(props.sdk, {
                 directory: dir,
@@ -1751,11 +1756,11 @@ export function SyncProvider(props: {
     const generation = ++globalBootstrapGeneration
     bootingRoot = true
     const globalActions = useGlobalSyncStore.getState().actions
-    bootstrapGlobal(props.sdk, (patch) => {
-      if (globalBootstrapGeneration === generation) {
-        globalActions.set(patch)
-      }
-    })
+    bootstrapGlobal(props.sdk, (patch) => {
+      if (globalBootstrapGeneration === generation) {
+        globalActions.set(patch)
+      }
+    })
       .then(() => {
         if (globalBootstrapGeneration === generation) {
           bootedAt = Date.now()
@@ -1771,7 +1776,7 @@ export function SyncProvider(props: {
         bootingRoot = false
       }
     }
-  }, [props.sdk])
+  }, [props.sdk])
 
   // Event pipeline — created once per mount. No class, no start/stop.
   // Abort controller owned by the pipeline closure. Cleanup aborts + flushes.
@@ -2177,6 +2182,77 @@ export function useSessions(directory?: string) {
   )
 }
 
+const selectPermissionRequestsBySession = (state: State) => state.permission
+const selectQuestionRequestsBySession = (state: State) => state.question
+
+type ScopedBlockingRequestCache<T extends { id: string }> = {
+  sessionID: string | null
+  sessions: Session[] | null
+  requestsBySession: Record<string, T[] | undefined> | null
+  result: T[]
+}
+
+function useScopedBlockingRequests<T extends { id: string }>(
+  sessionID: string | null,
+  directory: string | undefined,
+  selectRequestsBySession: (state: State) => Record<string, T[] | undefined>,
+  empty: T[],
+): T[] {
+  const cacheRef = useRef<ScopedBlockingRequestCache<T>>({
+    sessionID: null,
+    sessions: null,
+    requestsBySession: null,
+    result: empty,
+  })
+
+  return useDirectorySync(
+    useCallback((state: State) => {
+      const requestsBySession = selectRequestsBySession(state)
+      const cache = cacheRef.current
+      if (
+        cache.sessionID === sessionID
+        && cache.sessions === state.session
+        && cache.requestsBySession === requestsBySession
+      ) {
+        return cache.result
+      }
+
+      const next = collectScopedBlockingRequests(state.session, requestsBySession, sessionID, empty)
+      const result = areRequestArraysReferentiallyEqual(cache.result, next) ? cache.result : next
+      cacheRef.current = {
+        sessionID,
+        sessions: state.session,
+        requestsBySession,
+        result,
+      }
+      return result
+    }, [empty, selectRequestsBySession, sessionID]),
+    directory,
+  )
+}
+
+export function useScopedBlockingPermissions(sessionID: string | null, directory?: string): PermissionRequest[] {
+  return useScopedBlockingRequests(sessionID, directory, selectPermissionRequestsBySession, EMPTY_PERMISSION_REQUESTS)
+}
+
+export function useScopedBlockingQuestions(sessionID: string | null, directory?: string): QuestionRequest[] {
+  return useScopedBlockingRequests(sessionID, directory, selectQuestionRequestsBySession, EMPTY_QUESTION_REQUESTS)
+}
+
+export function useParentSession(sessionID: string | null, directory?: string): Session | null {
+  return useDirectorySync(
+    useCallback((state: State) => {
+      if (!sessionID) return null
+      const current = state.session.find((s) => s.id === sessionID)
+      if (!current?.parentID) return null
+      return state.session.find((s) => s.id === current.parentID)
+        ?? getAllSyncSessions().find((s) => s.id === current.parentID)
+        ?? null
+    }, [sessionID]),
+    directory,
+  )
+}
+
 const getSidebarSessionSignature = (session: Session, stableUpdatedAt: number): string => {
   const directory = (session as Session & { directory?: string | null }).directory ?? ''
   const parentID = (session as Session & { parentID?: string | null }).parentID ?? ''
@@ -2348,14 +2424,6 @@ const getConcatenatedTextFromParts = (parts: Part[]): string => {
   return text
 }
 
-const getFirstTextFromParts = (parts: Part[]): string => {
-  for (const part of parts) {
-    const text = getPartText(part)
-    if (text.length > 0) return text
-  }
-  return ""
-}
-
 type SessionMessageRecord = { info: Message; parts: Part[] }
 const EMPTY_SESSION_MESSAGE_RECORDS: SessionMessageRecord[] = []
 
@@ -2365,6 +2433,7 @@ type SessionMessageRecordsSnapshot = {
   visibleMessages: Message[]
   revertMessageID?: string
   suspendPartUpdates: boolean
+  suspendedPartUpdatesMessageID?: string
   list: SessionMessageRecord[]
   byId: Map<string, SessionMessageRecord>
 }
@@ -2376,8 +2445,12 @@ const MOBILE_SESSION_MESSAGE_RECORDS_CACHE_MAX = 4
 const MOBILE_SESSION_MESSAGE_RECORDS_CACHE_MAX_MESSAGES = 30
 const sessionMessageRecordsCache = new WeakMap<StoreApi<DirectoryStore>, Map<string, SessionMessageRecordsSnapshot>>()
 
-const getSessionMessageRecordsCacheKey = (sessionID: string, suspendPartUpdates: boolean): string => (
-  `${sessionID}\u0000${suspendPartUpdates ? 1 : 0}`
+const getSessionMessageRecordsCacheKey = (
+  sessionID: string,
+  suspendPartUpdates: boolean,
+  suspendedPartUpdatesMessageID?: string,
+): string => (
+  `${sessionID}\u0000${suspendPartUpdates ? 1 : 0}\u0000${suspendedPartUpdatesMessageID ?? ""}`
 )
 
 const getSessionMessageRecordsCache = (store: StoreApi<DirectoryStore>): Map<string, SessionMessageRecordsSnapshot> => {
@@ -2393,10 +2466,11 @@ const readCachedSessionMessageRecordsSnapshot = (
   store: StoreApi<DirectoryStore>,
   sessionID: string,
   suspendPartUpdates: boolean,
+  suspendedPartUpdatesMessageID?: string,
 ): SessionMessageRecordsSnapshot | undefined => {
   const cache = sessionMessageRecordsCache.get(store)
   if (!cache) return undefined
-  const key = getSessionMessageRecordsCacheKey(sessionID, suspendPartUpdates)
+  const key = getSessionMessageRecordsCacheKey(sessionID, suspendPartUpdates, suspendedPartUpdatesMessageID)
   const cached = cache.get(key)
   if (!cached) return undefined
   cache.delete(key)
@@ -2410,7 +2484,11 @@ const rememberSessionMessageRecordsSnapshot = (
 ): void => {
   if (!snapshot.sessionID) return
   const cache = getSessionMessageRecordsCache(store)
-  const key = getSessionMessageRecordsCacheKey(snapshot.sessionID, snapshot.suspendPartUpdates)
+  const key = getSessionMessageRecordsCacheKey(
+    snapshot.sessionID,
+    snapshot.suspendPartUpdates,
+    snapshot.suspendedPartUpdatesMessageID,
+  )
   const constrainedMaxMessages = isVSCodeRuntime()
     ? VSCODE_SESSION_MESSAGE_RECORDS_CACHE_MAX_MESSAGES
     : isMobileSurfaceRuntime()
@@ -2442,17 +2520,23 @@ export function dropCachedSessionMessageRecordsSnapshots(
   if (!cache) return
   for (const sessionID of sessionIDs) {
     if (!sessionID) continue
-    cache.delete(getSessionMessageRecordsCacheKey(sessionID, false))
-    cache.delete(getSessionMessageRecordsCacheKey(sessionID, true))
+    const prefix = `${sessionID}\u0000`
+    for (const key of [...cache.keys()]) {
+      if (key.startsWith(prefix)) {
+        cache.delete(key)
+      }
+    }
   }
 }
 
 const snapshotPartsMatchState = (snapshot: SessionMessageRecordsSnapshot, state: State): boolean => {
-  if (snapshot.suspendPartUpdates) {
-    return true
-  }
-
   for (const record of snapshot.list) {
+    if (snapshot.suspendPartUpdates) {
+      const suspendedID = snapshot.suspendedPartUpdatesMessageID
+      if (!suspendedID || record.info.id === suspendedID) {
+        continue
+      }
+    }
     if ((state.part[record.info.id] ?? EMPTY_PARTS) !== record.parts) {
       return false
     }
@@ -2466,8 +2550,9 @@ const getReusableSessionMessageRecordsSnapshot = (
   state: State,
   sessionID: string,
   suspendPartUpdates: boolean,
+  suspendedPartUpdatesMessageID?: string,
 ): SessionMessageRecordsSnapshot | undefined => {
-  const cached = readCachedSessionMessageRecordsSnapshot(store, sessionID, suspendPartUpdates)
+  const cached = readCachedSessionMessageRecordsSnapshot(store, sessionID, suspendPartUpdates, suspendedPartUpdatesMessageID)
   if (!cached) return undefined
   const sourceMessages = state.message[sessionID] ?? EMPTY_MESSAGES
   const session = state.session.find((candidate) => candidate.id === sessionID)
@@ -2476,6 +2561,7 @@ const getReusableSessionMessageRecordsSnapshot = (
     cached.sourceMessages === sourceMessages
     && cached.revertMessageID === revertMessageID
     && cached.suspendPartUpdates === suspendPartUpdates
+    && cached.suspendedPartUpdatesMessageID === suspendedPartUpdatesMessageID
     && snapshotPartsMatchState(cached, state)
   ) {
     return cached
@@ -2516,12 +2602,16 @@ export function buildSessionMessageRecordsSnapshot(
   sessionID: string,
   previous?: SessionMessageRecordsSnapshot,
   suspendPartUpdates = false,
+  suspendedPartUpdatesMessageID?: string,
 ): SessionMessageRecordsSnapshot {
   const { sourceMessages, visibleMessages, revertMessageID } = getVisibleMessagesForSession(state, sessionID, previous)
   const nextById = new Map<string, SessionMessageRecord>()
   const nextList = visibleMessages.map((message) => {
     const previousRecord = previous?.byId.get(message.id)
-    const parts = suspendPartUpdates && previousRecord
+    const shouldSuspendParts = suspendPartUpdates
+      && previousRecord
+      && (!suspendedPartUpdatesMessageID || message.id === suspendedPartUpdatesMessageID)
+    const parts = shouldSuspendParts
       ? previousRecord.parts
       : (state.part[message.id] ?? EMPTY_PARTS)
 
@@ -2535,6 +2625,8 @@ export function buildSessionMessageRecordsSnapshot(
 
   const unchanged = Boolean(previous)
     && previous?.visibleMessages === visibleMessages
+    && previous.suspendPartUpdates === suspendPartUpdates
+    && previous.suspendedPartUpdatesMessageID === suspendedPartUpdatesMessageID
     && previous.list.length === nextList.length
     && previous.list.every((record, index) => record === nextList[index])
 
@@ -2548,6 +2640,7 @@ export function buildSessionMessageRecordsSnapshot(
     visibleMessages,
     revertMessageID,
     suspendPartUpdates,
+    suspendedPartUpdatesMessageID,
     list: nextList,
     byId: nextById,
   }
@@ -2577,20 +2670,21 @@ export function useSessionTextMessages(sessionID: string, directory?: string): S
 }
 
 export function useUserMessageHistory(sessionID: string, directory?: string): string[] {
-  const records = useSessionMessageRecords(sessionID, directory)
-  const userMessages = useMemo(() => records.filter((record) => record.info.role === 'user'), [records])
+  const store = useDirectoryStore(directory)
+  const snapshotRef = useRef<UserMessageHistorySnapshot>(EMPTY_USER_MESSAGE_HISTORY_SNAPSHOT)
 
-  return useMemo(() => {
-    const history: string[] = []
-    for (let index = userMessages.length - 1; index >= 0; index -= 1) {
-      const message = userMessages[index]
-      const text = getFirstTextFromParts(message.parts)
-      if (text.length > 0) {
-        history.push(text)
-      }
-    }
-    return history
-  }, [userMessages])
+  const getSnapshot = useCallback(() => {
+    const next = buildUserMessageHistorySnapshot(store.getState(), sessionID, snapshotRef.current)
+    snapshotRef.current = next
+    return next.history
+  }, [sessionID, store])
+
+  const subscribe = useCallback((notify: () => void) => {
+    if (!sessionID) return () => undefined
+    return store.subscribe(notify)
+  }, [sessionID, store])
+
+  return React.useSyncExternalStore(subscribe, getSnapshot, getSnapshot)
 }
 
 /**
@@ -2603,7 +2697,7 @@ export function useUserMessageHistory(sessionID: string, directory?: string): st
 export function useSessionMessageRecords(
   sessionID: string,
   directory?: string,
-  options?: { suspendPartUpdates?: boolean },
+  options?: { suspendPartUpdates?: boolean; suspendPartUpdatesForMessageId?: string | null },
 ) {
   const store = useDirectoryStore(directory)
   const snapshotRef = useRef<SessionMessageRecordsSnapshot>({
@@ -2612,6 +2706,7 @@ export function useSessionMessageRecords(
     visibleMessages: EMPTY_MESSAGES,
     revertMessageID: undefined,
     suspendPartUpdates: Boolean(options?.suspendPartUpdates),
+    suspendedPartUpdatesMessageID: options?.suspendPartUpdatesForMessageId ?? undefined,
     list: [],
     byId: new Map(),
   })
@@ -2623,7 +2718,14 @@ export function useSessionMessageRecords(
 
     const state = store.getState()
     const suspendPartUpdates = Boolean(options?.suspendPartUpdates)
-    const reusableSnapshot = getReusableSessionMessageRecordsSnapshot(store, state, sessionID, suspendPartUpdates)
+    const suspendedPartUpdatesMessageID = options?.suspendPartUpdatesForMessageId ?? undefined
+    const reusableSnapshot = getReusableSessionMessageRecordsSnapshot(
+      store,
+      state,
+      sessionID,
+      suspendPartUpdates,
+      suspendedPartUpdatesMessageID,
+    )
     if (reusableSnapshot) {
       snapshotRef.current = reusableSnapshot
       return reusableSnapshot.list
@@ -2631,18 +2733,19 @@ export function useSessionMessageRecords(
 
     const previousSnapshot = snapshotRef.current.sessionID === sessionID
       ? snapshotRef.current
-      : readCachedSessionMessageRecordsSnapshot(store, sessionID, suspendPartUpdates)
+      : readCachedSessionMessageRecordsSnapshot(store, sessionID, suspendPartUpdates, suspendedPartUpdatesMessageID)
 
     const nextSnapshot = buildSessionMessageRecordsSnapshot(
       state,
       sessionID,
       previousSnapshot,
       suspendPartUpdates,
+      suspendedPartUpdatesMessageID,
     )
     snapshotRef.current = nextSnapshot
     rememberSessionMessageRecordsSnapshot(store, nextSnapshot)
     return nextSnapshot.list
-  }, [options?.suspendPartUpdates, sessionID, store])
+  }, [options?.suspendPartUpdates, options?.suspendPartUpdatesForMessageId, sessionID, store])
 
   const subscribe = useCallback((notify: () => void) => {
     if (!sessionID) return () => undefined
@@ -2671,6 +2774,7 @@ export function useEnsureSessionMessages(sessionID: string, directory?: string)
   const syncDirectory = useSyncDirectory()
   const resolvedDirectory = directory ?? syncDirectory
   const store = useDirectoryStore(resolvedDirectory)
+  const requestGenerationRef = React.useRef(0)
 
   React.useEffect(() => {
     if (!sessionID) return
@@ -2685,11 +2789,14 @@ export function useEnsureSessionMessages(sessionID: string, directory?: string)
     // Already loading this session for this directory
     if (_ensureMessagesLoading.has(loadingKey)) return
 
+    const generation = ++requestGenerationRef.current
+    const isStale = () => generation !== requestGenerationRef.current
+
     _ensureMessagesLoading.add(loadingKey)
 
     void (async () => {
       try {
-        await materializeSessionFromServer(resolvedDirectory, sessionID, store)
+        await materializeSessionFromServer(resolvedDirectory, sessionID, store, { isStale })
       } catch {
         // Transient failure — next navigation or reconnect will retry
       } finally {
diff --git a/packages/ui/src/sync/use-sync.ts b/packages/ui/src/sync/use-sync.ts
index 4e11beb9..b0d646d6 100644
--- a/packages/ui/src/sync/use-sync.ts
+++ b/packages/ui/src/sync/use-sync.ts
@@ -22,10 +22,11 @@ import {
 import { getSessionMaterializationStatus, materializeSessionSnapshots } from "./materialization"
 
 const SKIP_PARTS = new Set(["patch", "step-start", "step-finish"])
-const INITIAL_MESSAGE_PAGE_SIZE = 150
+const INITIAL_MESSAGE_PAGE_SIZE = 50
 const VSCODE_INITIAL_MESSAGE_PAGE_SIZE = 30
 const MOBILE_INITIAL_MESSAGE_PAGE_SIZE = 30
-const HISTORY_MESSAGE_PAGE_SIZE = 200
+const HISTORY_MESSAGE_PAGE_SIZE = 100
+const INITIAL_PAGE_EXPANSION_LIMITS = [100, 150] as const
 const VSCODE_INITIAL_PAGE_EXPANSION_LIMITS = [50, 80, 120] as const
 const MAX_SEEN_DIRS = 30
 const VSCODE_SESSION_CACHE_LIMIT = 4
@@ -40,6 +41,12 @@ const seenByDirectory = new Map<string, Set<string>>()
 // all request the same session during startup; coalesce them into one HTTP load.
 const syncSessionInflightByKey = new Map<string, Promise<void>>()
 
+// Per-session generation counter. When a newer syncSession request starts for
+// the same session, older in-flight requests become stale and must not write
+// to the store. This prevents rapid session switches (e.g. 1→2→3 in the
+// sidebar) from having each completed fetch fight for focus.
+const syncSessionGenerationByKey = new Map<string, number>()
+
 type SyncMeta = {
   limit: number
   cursor: string | undefined
@@ -88,6 +95,9 @@ const getInitialMessagePageSize = () => {
   if (isMobileSurfaceRuntime()) return MOBILE_INITIAL_MESSAGE_PAGE_SIZE
   return INITIAL_MESSAGE_PAGE_SIZE
 }
+const getInitialPageExpansionLimits = () => isConstrainedSessionRuntime()
+  ? VSCODE_INITIAL_PAGE_EXPANSION_LIMITS
+  : INITIAL_PAGE_EXPANSION_LIMITS
 const getDefaultMeta = (): SyncMeta => ({ limit: getInitialMessagePageSize(), cursor: undefined, complete: false, loading: false })
 
 function getPrefetchMeta(directory: string, sessionID: string): SyncMeta | undefined {
@@ -333,7 +343,7 @@ export function useSync() {
 
   // Load messages for a session
   const loadMessages = useCallback(
-    async (sessionID: string, options?: { before?: string; mode?: "replace" | "prepend" }) => {
+    async (sessionID: string, options?: { before?: string; mode?: "replace" | "prepend"; isStale?: () => boolean }) => {
       const m = getMetaFor(sessionID)
       if (m.loading) return
       setMetaFor(sessionID, { loading: true })
@@ -342,13 +352,13 @@ export function useSync() {
         const limit = options?.before ? HISTORY_MESSAGE_PAGE_SIZE : m.limit
         let page = await fetchMessages(sessionID, limit, options?.before)
 
-        // Constrained shells keep the initial page small for switch performance. Some
-        // sessions have a very large final turn, so the latest 30 records can
+        // Keep the initial page small for switch performance. Some sessions
+        // have a very large final turn, so the latest records can
         // contain only assistant/tool records and no user boundary. That makes
         // turn projection render an empty chat until the user manually loads
         // older messages. Expand only this initial tail fetch, with a hard cap.
-        if (!options?.before && isConstrainedSessionRuntime() && !page.complete && !hasUserMessage(page.session)) {
-          for (const nextLimit of VSCODE_INITIAL_PAGE_EXPANSION_LIMITS) {
+        if (!options?.before && !page.complete && !hasUserMessage(page.session)) {
+          for (const nextLimit of getInitialPageExpansionLimits()) {
             if (nextLimit <= limit) continue
             page = await fetchMessages(sessionID, nextLimit)
             if (page.complete || hasUserMessage(page.session)) break
@@ -362,6 +372,11 @@ export function useSync() {
           clearOptimistic(sessionID, messageID)
         }
 
+        if (options?.isStale?.()) {
+          setMetaFor(sessionID, { loading: false })
+          return
+        }
+
         const current = store.getState()
         const materialized = materializeSessionSnapshots(
           current,
@@ -373,6 +388,11 @@ export function useSync() {
           { skipPartTypes: SKIP_PARTS, mode: options?.mode === "prepend" ? "prepend" : "merge" },
         )
 
+        if (options?.isStale?.()) {
+          setMetaFor(sessionID, { loading: false })
+          return
+        }
+
         setMetaFor(sessionID, {
           limit: materialized.messages.length,
           cursor: merged.cursor,
@@ -404,6 +424,13 @@ export function useSync() {
       const existing = syncSessionInflightByKey.get(key)
       if (existing) return existing
 
+      // This is a new request. Bump generation so any older request that
+      // might still be finishing (e.g. from a previous component lifecycle)
+      // knows it is stale and should not write to the store.
+      const generation = (syncSessionGenerationByKey.get(key) ?? 0) + 1
+      syncSessionGenerationByKey.set(key, generation)
+      const isStale = () => syncSessionGenerationByKey.get(key) !== generation
+
       const current = store.getState()
       const m = getMetaFor(sessionID)
       const materialization = getSessionMaterializationStatus(current, sessionID)
@@ -449,7 +476,7 @@ export function useSync() {
                     assertSdkSuccess(response, "session.get")
                     return response
                   })
-                  if (result.data) {
+                  if (result.data && !isStale()) {
                     const nextSession = stripSessionDiffSnapshots(result.data)
                     const s = store.getState()
                     const sessions = [...s.session]
@@ -459,15 +486,30 @@ export function useSync() {
                     } else {
                       sessions.splice(idx.index, 0, nextSession)
                     }
-                    store.setState({ session: sessions })
+                    if (!isStale()) {
+                      store.setState({ session: sessions })
+                    }
                   }
                 } catch (e) {
                   console.error("[sync] failed to fetch session", sessionID, e)
                 }
               })()
             : Promise.resolve(),
-          shouldLoadMessages ? loadMessages(sessionID) : Promise.resolve(),
+          shouldLoadMessages ? loadMessages(sessionID, { isStale }) : Promise.resolve(),
         ])
+
+        // Progressive mount: after the initial page resolves, if the session
+        // isn't stale and the server indicated more messages, dispatch a
+        // second fetch to prepend older history. The user sees the first page
+        // immediately; the rest arrive shortly after. This gives the scroll
+        // container headroom above the viewport so the "load older on
+        // scroll-up" trigger fires before the user hits the absolute top.
+        if (!isStale()) {
+          const currentMeta = getMetaFor(sessionID)
+          if (currentMeta.cursor && !currentMeta.complete) {
+            loadMessages(sessionID, { before: currentMeta.cursor, mode: "prepend", isStale })
+          }
+        }
       })()
 
       syncSessionInflightByKey.set(key, promise)
diff --git a/packages/ui/src/sync/user-message-history.test.ts b/packages/ui/src/sync/user-message-history.test.ts
new file mode 100644
index 00000000..8d46e225
--- /dev/null
+++ b/packages/ui/src/sync/user-message-history.test.ts
@@ -0,0 +1,98 @@
+import { describe, expect, test } from 'bun:test';
+import type { Message, Part } from '@opencode-ai/sdk/v2/client';
+import type { State } from './types';
+
+import { EMPTY_USER_MESSAGE_HISTORY_SNAPSHOT, buildUserMessageHistorySnapshot } from './user-message-history';
+
+const message = (id: string, role: 'user' | 'assistant'): Message => ({
+  id,
+  role,
+  sessionID: 'ses_1',
+  time: { created: 1 },
+} as Message);
+
+const textPart = (id: string, text: string): Part => ({
+  id,
+  type: 'text',
+  text,
+} as Part);
+
+const state = (partial: Partial<State>): Pick<State, 'session' | 'message' | 'part'> => ({
+  session: [],
+  message: {},
+  part: {},
+  ...partial,
+});
+
+describe('buildUserMessageHistorySnapshot', () => {
+  test('returns a shared empty snapshot without a session id', () => {
+    expect(buildUserMessageHistorySnapshot(state({}), '')).toBe(EMPTY_USER_MESSAGE_HISTORY_SNAPSHOT);
+  });
+
+  test('keeps history stable when assistant parts change', () => {
+    const user = message('user_1', 'user');
+    const assistant = message('assistant_1', 'assistant');
+    const userParts = [textPart('part_user', 'hello')];
+    const first = buildUserMessageHistorySnapshot(
+      state({
+        message: { ses_1: [user, assistant] },
+        part: { user_1: userParts, assistant_1: [textPart('part_a', 'stream')] },
+      }),
+      'ses_1',
+    );
+
+    const second = buildUserMessageHistorySnapshot(
+      state({
+        message: { ses_1: [user, assistant] },
+        part: { user_1: userParts, assistant_1: [textPart('part_a2', 'streaming')] },
+      }),
+      'ses_1',
+      first,
+    );
+
+    expect(second).toBe(first);
+    expect(second.history).toEqual(['hello']);
+  });
+
+  test('updates history when a user part changes', () => {
+    const user = message('user_1', 'user');
+    const first = buildUserMessageHistorySnapshot(
+      state({
+        message: { ses_1: [user] },
+        part: { user_1: [textPart('part_user', 'hello')] },
+      }),
+      'ses_1',
+    );
+
+    const second = buildUserMessageHistorySnapshot(
+      state({
+        message: { ses_1: [user] },
+        part: { user_1: [textPart('part_user_updated', 'updated')] },
+      }),
+      'ses_1',
+      first,
+    );
+
+    expect(second).not.toBe(first);
+    expect(second.history).toEqual(['updated']);
+  });
+
+  test('excludes user messages hidden by session revert state', () => {
+    const beforeRevert = message('user_1', 'user');
+    const reverted = message('user_2', 'user');
+
+    const snapshot = buildUserMessageHistorySnapshot(
+      state({
+        session: [{ id: 'ses_1', revert: { messageID: 'user_2' } } as State['session'][number]],
+        message: { ses_1: [beforeRevert, reverted] },
+        part: {
+          user_1: [textPart('part_user_1', 'kept')],
+          user_2: [textPart('part_user_2', 'reverted')],
+        },
+      }),
+      'ses_1',
+    );
+
+    expect(snapshot.history).toEqual(['kept']);
+  });
+});
diff --git a/packages/ui/src/sync/user-message-history.ts b/packages/ui/src/sync/user-message-history.ts
new file mode 100644
index 00000000..20abbfdf
--- /dev/null
+++ b/packages/ui/src/sync/user-message-history.ts
@@ -0,0 +1,98 @@
+import type { Message, Part } from '@opencode-ai/sdk/v2/client';
+import type { State } from './types';
+
+type UserMessageHistoryRecord = {
+  message: Message;
+  parts: Part[];
+};
+
+export type UserMessageHistorySnapshot = {
+  sessionID: string;
+  revertMessageID?: string;
+  records: UserMessageHistoryRecord[];
+  history: string[];
+};
+
+const EMPTY_PARTS: Part[] = [];
+const EMPTY_RECORDS: UserMessageHistoryRecord[] = [];
+const EMPTY_HISTORY: string[] = [];
+
+export const EMPTY_USER_MESSAGE_HISTORY_SNAPSHOT: UserMessageHistorySnapshot = {
+  sessionID: '',
+  revertMessageID: undefined,
+  records: EMPTY_RECORDS,
+  history: EMPTY_HISTORY,
+};
+
+const getPartText = (part: Part): string => {
+  if (part?.type !== 'text') return '';
+  const text = (part as { text?: unknown }).text;
+  return typeof text === 'string' ? text : '';
+};
+
+const getFirstTextFromParts = (parts: Part[]): string => {
+  for (const part of parts) {
+    const text = getPartText(part);
+    if (text.length > 0) return text;
+  }
+  return '';
+};
+
+const areRecordsEqual = (left: UserMessageHistoryRecord[], right: UserMessageHistoryRecord[]): boolean => {
+  if (left === right) return true;
+  if (left.length !== right.length) return false;
+  for (let index = 0; index < left.length; index += 1) {
+    if (left[index]?.message !== right[index]?.message || left[index]?.parts !== right[index]?.parts) {
+      return false;
+    }
+  }
+  return true;
+};
+
+export const buildUserMessageHistorySnapshot = (
+  state: Pick<State, 'session' | 'message' | 'part'>,
+  sessionID: string,
+  previous: UserMessageHistorySnapshot = EMPTY_USER_MESSAGE_HISTORY_SNAPSHOT,
+): UserMessageHistorySnapshot => {
+  if (!sessionID) {
+    return EMPTY_USER_MESSAGE_HISTORY_SNAPSHOT;
+  }
+
+  const messages = state.message[sessionID] ?? [];
+  const session = state.session.find((candidate) => candidate.id === sessionID);
+  const revertMessageID = (session as { revert?: { messageID?: string } } | undefined)?.revert?.messageID;
+  const records: UserMessageHistoryRecord[] = [];
+  for (let index = messages.length - 1; index >= 0; index -= 1) {
+    const message = messages[index];
+    if (message.role !== 'user') {
+      continue;
+    }
+    if (revertMessageID && message.id >= revertMessageID) {
+      continue;
+    }
+    records.push({
+      message,
+      parts: state.part[message.id] ?? EMPTY_PARTS,
+    });
+  }
+
+  if (records.length === 0) {
+    return previous.sessionID === sessionID && previous.revertMessageID === revertMessageID && previous.records.length === 0
+      ? previous
+      : { sessionID, revertMessageID, records: EMPTY_RECORDS, history: EMPTY_HISTORY };
+  }
+
+  if (previous.sessionID === sessionID && previous.revertMessageID === revertMessageID && areRecordsEqual(previous.records, records)) {
+    return previous;
+  }
+
+  const history: string[] = [];
+  for (const record of records) {
+    const text = getFirstTextFromParts(record.parts);
+    if (text.length > 0) {
+      history.push(text);
+    }
+  }
+
+  return { sessionID, revertMessageID, records, history };
+};