perf(sessions): archive a worktree's sessions through one server batch

Removing a worktree archived its sessions one SDK call at a time and
then re-rendered the whole sidebar once per streamed session.updated
echo. On a worktree with 121 sessions that meant 14.8s of main-thread
work, 121 requests, and 328 localStorage writes.

- Add POST /api/openchamber/sessions/archive: validates a batch (max
  500 ids, per-request archivedAt), archives sequentially, and reports
  partial failures instead of dropping the batch. VS Code serves no
  such route and answers 501; the shared UI then falls back to the
  per-session path.
- Plan batches from the sessions this client actually holds, live
  directory stores first, so worktree-only sessions still batch.
- Claim (id, archivedAt) pairs before the request and consume the
  matching session.updated echoes, so the server's own confirmations
  no longer fan out into 121 store publications. Runtime-scoped, TTL
  30s, released on response or fallback; non-matching updates pass.
- Make the managed-chats persistence a real trailing debounce instead
  of a 50ms throttle, so a burst of publications coalesces into one
  localStorage write.

Benchmark (121 sessions, production build, real Chrome): 14785ms ->
~1030ms, long tasks 100 -> 1, global store publications 236 -> 1,
persistence writes 328 -> 3.

packages/ui/src/sync/__tests__/sync-context-session-events.test.ts

@@ -45,7 +45,15 @@ mock.module("@/lib/runtime-switch", () => ({
     return () => undefined
   },
 }))
-import { applySessionEventsToGlobalSessions, applySessionEventToGlobalSessions } from "../session-event-router"
+import {
+  applySessionEventsToGlobalSessions,
+  applySessionEventToGlobalSessions,
+} from "../session-event-router"
+import {
+  registerBulkArchiveEchoes,
+  releaseBulkArchiveEchoes,
+  shouldConsumeBulkArchiveEcho,
+} from "../bulk-archive-echo"
 
 const buildSession = (title: string, time: Session["time"]): Session => ({
   id: "ses_1",
@@ -146,4 +154,35 @@ describe("applySessionEventToGlobalSessions", () => {
     expect(mutationCalls).toBe(1)
     expect(upsertedSessions).toHaveLength(1_000)
   })
+
+  test("consumes only the matching bulk archive echo", () => {
+    registerBulkArchiveEchoes(runtimeKey, [{ id: "ses_1", archivedAt: 20 }], 100)
+
+    expect(shouldConsumeBulkArchiveEcho(buildEvent(buildSession("Initial", {
+      created: 1,
+      updated: 20,
+      archived: 20,
+    })), runtimeKey, 101)).toBe(true)
+    expect(shouldConsumeBulkArchiveEcho(buildEvent(buildSession("Initial", {
+      created: 1,
+      updated: 21,
+      archived: 21,
+    })), runtimeKey, 101)).toBe(false)
+    expect(shouldConsumeBulkArchiveEcho(buildEvent(buildSession("Initial", {
+      created: 1,
+      updated: 20,
+      archived: 20,
+    })), "runtime-b", 101)).toBe(false)
+  })
+
+  test("does not consume an expired or released bulk archive echo", () => {
+    registerBulkArchiveEchoes(runtimeKey, [{ id: "ses_1", archivedAt: 20 }], 100)
+    const event = buildEvent(buildSession("Initial", { created: 1, updated: 20, archived: 20 }))
+
+    expect(shouldConsumeBulkArchiveEcho(event, runtimeKey, 30_101)).toBe(false)
+
+    registerBulkArchiveEchoes(runtimeKey, [{ id: "ses_1", archivedAt: 20 }], 100)
+    releaseBulkArchiveEchoes(runtimeKey, ["ses_1"])
+    expect(shouldConsumeBulkArchiveEcho(event, runtimeKey, 101)).toBe(false)
+  })
 })

packages/ui/src/sync/bulk-archive-echo.ts

@@ -0,0 +1,49 @@
+import type { Event } from "@opencode-ai/sdk/v2/client"
+import { subscribeRuntimeEndpointWillChange } from "@/lib/runtime-switch"
+
+const BULK_ARCHIVE_ECHO_TTL_MS = 30_000
+const pendingEchoes = new Map<string, Map<string, { archivedAt: number; expiresAt: number }>>()
+
+subscribeRuntimeEndpointWillChange(() => pendingEchoes.clear())
+
+export const registerBulkArchiveEchoes = (
+  runtimeKey: string,
+  sessions: Iterable<{ id: string; archivedAt: number }>,
+  now = Date.now(),
+): void => {
+  let runtimeEchoes = pendingEchoes.get(runtimeKey)
+  if (!runtimeEchoes) {
+    runtimeEchoes = new Map()
+    pendingEchoes.set(runtimeKey, runtimeEchoes)
+  }
+  for (const session of sessions) {
+    runtimeEchoes.set(session.id, {
+      archivedAt: session.archivedAt,
+      expiresAt: now + BULK_ARCHIVE_ECHO_TTL_MS,
+    })
+  }
+}
+
+export const releaseBulkArchiveEchoes = (runtimeKey: string, sessionIds: Iterable<string>): void => {
+  const runtimeEchoes = pendingEchoes.get(runtimeKey)
+  if (!runtimeEchoes) return
+  for (const sessionId of sessionIds) runtimeEchoes.delete(sessionId)
+  if (runtimeEchoes.size === 0) pendingEchoes.delete(runtimeKey)
+}
+
+export const shouldConsumeBulkArchiveEcho = (
+  event: Event,
+  runtimeKey: string,
+  now = Date.now(),
+): boolean => {
+  if (event.type !== "session.updated") return false
+  const runtimeEchoes = pendingEchoes.get(runtimeKey)
+  const expected = runtimeEchoes?.get(event.properties.info.id)
+  if (!expected) return false
+  if (expected.expiresAt < now) {
+    runtimeEchoes?.delete(event.properties.info.id)
+    if (runtimeEchoes?.size === 0) pendingEchoes.delete(runtimeKey)
+    return false
+  }
+  return event.properties.info.time.archived === expected.archivedAt
+}

packages/ui/src/sync/persist-cache.test.ts

@@ -92,6 +92,16 @@ describe("persisted directory sessions", () => {
     expect(readManagedChatSessions()).toEqual([])
   })
 
+  test("coalesces a continuing burst into one trailing session write", async () => {
+    persistSessions(directory, [session(1, 1)])
+    await new Promise((resolve) => setTimeout(resolve, 30))
+    persistSessions(directory, [session(1, 2)])
+    await waitForPersistence()
+
+    expect(storage.writes).toBe(1)
+    expect(readDirCache(directory).sessions?.[0]?.time.updated).toBe(2)
+  })
+
   test("keeps the 50 most recently updated sessions across restart reads", async () => {
     const sessions = Array.from({ length: 60 }, (_, updated) => session(59 - updated, updated))
 

packages/ui/src/sync/persist-cache.ts

@@ -177,7 +177,7 @@ function scheduleSessionCacheWrite(directory: string, sessions: Session[]): void
     if (pending.runtimeKey !== runtimeKey) pendingSessionWrites.delete(pendingKey)
   }
   pendingSessionWrites.set(key, { runtimeKey, key, legacyKey: legacyCacheKey(directory, "sessions"), sessions })
-  if (pendingSessionWriteTimer !== undefined) return
+  if (pendingSessionWriteTimer !== undefined) clearTimeout(pendingSessionWriteTimer)
   pendingSessionWriteTimer = setTimeout(flushPendingSessionWrites, SESSION_PERSIST_DEBOUNCE_MS)
 }
 

packages/ui/src/sync/session-actions.test.ts

@@ -21,7 +21,16 @@ let sessionDeleteError: unknown | null = null
 let beforeSessionUpdateResolve: ((sessionId: string) => void) | null = null
 let beforeSessionDeleteResolve: ((sessionId: string) => void) | null = null
 const globalUpsertedSessions: unknown[] = []
+const globalUpsertedSessionBatches: Session[][] = []
 const globalRemovedSessionIds: string[] = []
+// Sessions this client is holding. `archiveSessions` reads them to decide which
+// sessions can be archived by the server in one batch.
+let globalActiveSessions: Session[] = []
+const archiveBatchRequests: Array<{ directory: string; ids: string[] }> = []
+let archiveBatchResponse: { status: number; body: unknown } = {
+  status: 404,
+  body: { error: 'not found' },
+}
 const deletedCleanupIdentities: Array<{ runtimeKey: string; directory: string; sessionId: string }> = []
 const movedSessionDirectories: Array<{ sessionID: string; directory: string }> = []
 
@@ -243,11 +252,15 @@ mock.module("@/stores/useGlobalSessionsStore", () => ({
   },
   useGlobalSessionsStore: {
     getState: () => ({
-      activeSessions: [],
+      activeSessions: globalActiveSessions,
       archivedSessions: [],
       upsertSession: (session: unknown) => {
         globalUpsertedSessions.push(session)
       },
+      upsertSessions: (sessions: Session[]) => {
+        globalUpsertedSessionBatches.push(sessions)
+        globalUpsertedSessions.push(...sessions)
+      },
       removeSessions: (ids: Iterable<string>) => {
         globalRemovedSessionIds.push(...ids)
       },
@@ -255,6 +268,18 @@ mock.module("@/stores/useGlobalSessionsStore", () => ({
   },
 }))
 
+mock.module("@/lib/runtime-fetch", () => ({
+  runtimeFetch: async (path: string, init?: { body?: string }) => {
+    const payload = JSON.parse(String(init?.body ?? "{}"))
+    archiveBatchRequests.push({ directory: payload.directory, ids: payload.ids })
+    void path
+    return new Response(JSON.stringify(archiveBatchResponse.body), {
+      status: archiveBatchResponse.status,
+      headers: { "content-type": "application/json" },
+    })
+  },
+}))
+
 mock.module("./session-deletion-cleanup", () => ({
   cleanupPersistedSessionState: (identity: { runtimeKey: string; directory: string; sessionId: string }) => {
     deletedCleanupIdentities.push(identity)
@@ -396,6 +421,10 @@ describe("confirmed session removal", () => {
     sessionUpdateResult = {}
     beforeSessionUpdateResolve = null
     beforeSessionDeleteResolve = null
+    globalUpsertedSessionBatches.length = 0
+    globalActiveSessions = []
+    archiveBatchRequests.length = 0
+    archiveBatchResponse = { status: 404, body: { error: 'not found' } }
   })
 
   test("does not remove live or persisted state when delete fails", async () => {
@@ -636,6 +665,161 @@ describe("confirmed session removal", () => {
   })
 })
 
+describe("archiving a batch through the server", () => {
+  const liveSession = (id: string, metadata?: Record<string, unknown>): Session => ({
+    id,
+    directory: "/test/project",
+    time: { created: 1 },
+    ...(metadata ? { metadata } : {}),
+  } as unknown as Session)
+
+  const archivedSession = (id: string): Session => ({
+    id,
+    directory: "/test/project",
+    time: { created: 1, archived: 2 },
+  } as unknown as Session)
+
+  beforeEach(() => {
+    replyCalls.length = 0
+    globalUpsertedSessions.length = 0
+    globalUpsertedSessionBatches.length = 0
+    globalActiveSessions = []
+    archiveBatchRequests.length = 0
+    archiveBatchResponse = { status: 404, body: { error: "not found" } }
+    sessionUpdateResult = {}
+    beforeSessionUpdateResolve = null
+  })
+
+  test("archives held sessions in one request and reconciles the stores once", async () => {
+    globalActiveSessions = [liveSession("session-a"), liveSession("session-b")]
+    archiveBatchResponse = {
+      status: 200,
+      body: { archived: [archivedSession("session-a"), archivedSession("session-b")], failedIds: [] },
+    }
+    const source = createStore({}, { session: [liveSession("session-a"), liveSession("session-b")] })
+    const { archiveSessions, setActionRefs } = await import("./session-actions")
+    setActionRefs(mockSdk as unknown as OpencodeClient, createChildStores([["/test/project", source]]), () => "/test/project")
+
+    const result = await archiveSessions(["session-a", "session-b"])
+
+    expect(result).toEqual({ archivedIds: ["session-a", "session-b"], failedIds: [] })
+    expect(archiveBatchRequests).toEqual([{ directory: "/test/project", ids: ["session-a", "session-b"] }])
+    // The point of the batch: no per-session SDK call, and one store write for
+    // the whole set instead of one per session.
+    expect(replyCalls.filter((call) => call.method === "session.update")).toEqual([])
+    expect(globalUpsertedSessionBatches).toHaveLength(1)
+    expect(source.getState().session).toEqual([])
+    expect(source.getState().sessionRevision).toBe(1)
+  })
+
+  test("batches sessions held only by the live directory store", async () => {
+    archiveBatchResponse = {
+      status: 200,
+      body: { archived: [archivedSession("session-a")], failedIds: [] },
+    }
+    const source = createStore({}, { session: [liveSession("session-a")] })
+    const { archiveSessions, setActionRefs } = await import("./session-actions")
+    setActionRefs(mockSdk as unknown as OpencodeClient, createChildStores([["/test/project", source]]), () => "/test/project")
+
+    const result = await archiveSessions(["session-a"])
+
+    expect(result).toEqual({ archivedIds: ["session-a"], failedIds: [] })
+    expect(archiveBatchRequests).toEqual([{ directory: "/test/project", ids: ["session-a"] }])
+    expect(replyCalls.filter((call) => call.method === "session.update")).toEqual([])
+  })
+
+  test("reports the sessions the server could not archive without losing the rest", async () => {
+    globalActiveSessions = [liveSession("session-a"), liveSession("session-b")]
+    archiveBatchResponse = {
+      status: 200,
+      body: { archived: [archivedSession("session-a")], failedIds: ["session-b"] },
+    }
+    const source = createStore({}, { session: [liveSession("session-a"), liveSession("session-b")] })
+    const { archiveSessions, setActionRefs } = await import("./session-actions")
+    setActionRefs(mockSdk as unknown as OpencodeClient, createChildStores([["/test/project", source]]), () => "/test/project")
+
+    const result = await archiveSessions(["session-a", "session-b"])
+
+    expect(result).toEqual({ archivedIds: ["session-a"], failedIds: ["session-b"] })
+    expect(source.getState().session.map((item) => item.id)).toEqual(["session-b"])
+  })
+
+  test("falls back to archiving one by one when the runtime does not serve the route", async () => {
+    globalActiveSessions = [liveSession("session-a"), liveSession("session-b")]
+    archiveBatchResponse = { status: 501, body: { error: "not supported in VS Code" } }
+    sessionUpdateResult = { data: archivedSession("session-a") }
+    const source = createStore({}, { session: [liveSession("session-a"), liveSession("session-b")] })
+    const { archiveSessions, setActionRefs } = await import("./session-actions")
+    setActionRefs(mockSdk as unknown as OpencodeClient, createChildStores([["/test/project", source]]), () => "/test/project")
+
+    const result = await archiveSessions(["session-a", "session-b"])
+
+    expect(result).toEqual({ archivedIds: ["session-a", "session-b"], failedIds: [] })
+    expect(replyCalls.filter((call) => call.method === "session.update").map((call) => call.params.sessionID))
+      .toEqual(["session-a", "session-b"])
+    expect(source.getState().session).toEqual([])
+  })
+
+  test("treats a malformed batch answer as unavailable instead of as an empty success", async () => {
+    globalActiveSessions = [liveSession("session-a")]
+    archiveBatchResponse = { status: 200, body: { archived: [{ title: "no id" }], failedIds: [] } }
+    sessionUpdateResult = { data: archivedSession("session-a") }
+    const source = createStore({}, { session: [liveSession("session-a")] })
+    const { archiveSessions, setActionRefs } = await import("./session-actions")
+    setActionRefs(mockSdk as unknown as OpencodeClient, createChildStores([["/test/project", source]]), () => "/test/project")
+
+    const result = await archiveSessions(["session-a"])
+
+    expect(result).toEqual({ archivedIds: ["session-a"], failedIds: [] })
+    expect(replyCalls.filter((call) => call.method === "session.update").map((call) => call.params.sessionID))
+      .toEqual(["session-a"])
+  })
+
+  test("keeps review and btw sessions on the per-session path", async () => {
+    const review = liveSession("session-review", { openchamber: { kind: "review", originalSessionID: "session-parent" } })
+    const parentWithFork = liveSession("session-parent", { openchamber: { btwSessionID: "session-fork" } })
+    globalActiveSessions = [liveSession("session-plain"), review, parentWithFork]
+    archiveBatchResponse = {
+      status: 200,
+      body: { archived: [archivedSession("session-plain")], failedIds: [] },
+    }
+    sessionUpdateResult = { data: archivedSession("session-review") }
+    const source = createStore({}, { session: [liveSession("session-plain"), review, parentWithFork] })
+    const { archiveSessions, setActionRefs } = await import("./session-actions")
+    setActionRefs(mockSdk as unknown as OpencodeClient, createChildStores([["/test/project", source]]), () => "/test/project")
+
+    await archiveSessions(["session-plain", "session-review", "session-parent"])
+
+    // Unlinking a partner rewrites another session's metadata, so those two
+    // never travel in the batch.
+    expect(archiveBatchRequests).toEqual([{ directory: "/test/project", ids: ["session-plain"] }])
+    expect(replyCalls.filter((call) => call.method === "session.update").map((call) => call.params.sessionID))
+      .toEqual(["session-review", "session-parent"])
+  })
+
+  test("does not reconcile a batch answered after a runtime switch", async () => {
+    globalActiveSessions = [liveSession("session-a")]
+    archiveBatchResponse = {
+      status: 200,
+      body: { archived: [archivedSession("session-a")], failedIds: [] },
+    }
+    const source = createStore({}, { session: [liveSession("session-a")] })
+    const { getRuntimeKey, switchRuntimeEndpoint } = await import("../lib/runtime-switch")
+    switchRuntimeEndpoint({ apiBaseUrl: "http://archive-bulk-a.test", runtimeKey: "archive-bulk-a" })
+    const capturedRuntimeKey = getRuntimeKey()
+    const { archiveSessions, setActionRefs } = await import("./session-actions")
+    setActionRefs(mockSdk as unknown as OpencodeClient, createChildStores([["/test/project", source]]), () => "/test/project")
+
+    const pending = archiveSessions(["session-a"], { expectedRuntimeKey: capturedRuntimeKey })
+    switchRuntimeEndpoint({ apiBaseUrl: "http://archive-bulk-b.test", runtimeKey: "archive-bulk-b" })
+    const result = await pending
+
+    expect(result).toEqual({ archivedIds: [], failedIds: ["session-a"] })
+    expect(source.getState().session.map((item) => item.id)).toEqual(["session-a"])
+    expect(globalUpsertedSessionBatches).toEqual([])
+  })
+})
+
 describe("session restore (unarchive)", () => {
   beforeEach(() => {
     replyCalls.length = 0

packages/ui/src/sync/session-actions.ts

@@ -33,6 +33,8 @@ import { getBtwOriginalSessionID, getBtwSessionID, isBtwSession, withoutBtwSessi
 import { withLinkedIssue, type LinkedIssue } from "@/lib/linkedIssues"
 import { getImperativeSessionMessageLoader } from "./session-message-loader"
 import { cleanupPersistedSessionState } from "./session-deletion-cleanup"
+import { requestSessionArchiveBatch } from "./session-archive-batch"
+import { registerBulkArchiveEchoes, releaseBulkArchiveEchoes } from "./bulk-archive-echo"
 import { getRuntimeKey } from "@/lib/runtime-switch"
 import { markAmbiguousTransportFailure } from "@/lib/relay/transport-error"
 import { getErrorStatus, isAmbiguousSendFailure } from "./send-failure-classification"
@@ -75,20 +77,29 @@ let _optimisticAdd: ((input: OptimisticAddInput) => void) | null = null
 let _optimisticRemove: ((input: OptimisticRemoveInput) => void) | null = null
 let _optimisticConfirm: ((input: OptimisticConfirmInput) => void) | null = null
 
-function sessionMutationPatch(
+/**
+ * Revision patch for one or more sessions changing in the same store write.
+ *
+ * A batch bumps the revision once, because it is one state change: consumers
+ * compare revisions to decide whether their view of the list is stale, and a
+ * batch leaves them stale exactly once rather than once per session.
+ */
+function sessionsMutationPatch(
   state: ReturnType<DirectoryStoreApi["getState"]>,
-  sessionId: string,
+  sessionIds: Iterable<string>,
   deleted: boolean,
 ) {
   const revision = (state.sessionRevision ?? 0) + 1
   const sessionEventRevision = { ...(state.sessionEventRevision ?? {}) }
   const sessionDeletedRevision = { ...(state.sessionDeletedRevision ?? {}) }
-  if (deleted) {
-    sessionDeletedRevision[sessionId] = revision
-    delete sessionEventRevision[sessionId]
-  } else {
-    sessionEventRevision[sessionId] = revision
-    delete sessionDeletedRevision[sessionId]
+  for (const sessionId of sessionIds) {
+    if (deleted) {
+      sessionDeletedRevision[sessionId] = revision
+      delete sessionEventRevision[sessionId]
+    } else {
+      sessionEventRevision[sessionId] = revision
+      delete sessionDeletedRevision[sessionId]
+    }
   }
   return {
     sessionListSource: "live" as const,
@@ -98,6 +109,14 @@ function sessionMutationPatch(
   }
 }
 
+function sessionMutationPatch(
+  state: ReturnType<DirectoryStoreApi["getState"]>,
+  sessionId: string,
+  deleted: boolean,
+) {
+  return sessionsMutationPatch(state, [sessionId], deleted)
+}
+
 function invalidateSessionLoads(sessionId: string, directories: Iterable<string | null | undefined>): void {
   const loader = getImperativeSessionMessageLoader()
   if (!loader) return
@@ -1039,6 +1058,50 @@ function removeSessionFromLiveStores(sessionId: string, preferredDirectory?: str
   return snapshots
 }
 
+/**
+ * Remove a batch of server-confirmed sessions from every live child store.
+ *
+ * Each affected store is written once for the whole batch. Removing the
+ * sessions one at a time notified every subscriber — and therefore re-rendered
+ * the sidebar — once per session, which is what made archiving a worktree's
+ * sessions block the main thread for seconds.
+ */
+function removeSessionsFromLiveStores(sessionIds: Iterable<string>, preferredDirectory?: string): SessionListSnapshot[] {
+  const ids = new Set(sessionIds)
+  if (!_childStores || ids.size === 0) return []
+
+  const snapshots: SessionListSnapshot[] = []
+  const visited = new Set<string>()
+  const candidates: Array<[string, DirectoryStoreApi]> = []
+
+  if (preferredDirectory) {
+    const preferredStore = _childStores.children.get(preferredDirectory)
+    if (preferredStore) {
+      candidates.push([preferredDirectory, preferredStore])
+      visited.add(preferredDirectory)
+    }
+  }
+
+  for (const entry of _childStores.children.entries()) {
+    if (visited.has(entry[0])) continue
+    candidates.push(entry)
+  }
+
+  for (const [directory, store] of candidates) {
+    const current = store.getState()
+    const removed = current.session.filter((session) => ids.has(session.id)).map((session) => session.id)
+    if (removed.length === 0) continue
+
+    snapshots.push({ directory })
+    store.setState({
+      session: current.session.filter((session) => !ids.has(session.id)),
+      ...sessionsMutationPatch(current, removed, true),
+    })
+  }
+
+  return snapshots
+}
+
 function cleanupSessionWorktreeMetadata(sessionId: string): void {
   useSessionUIStore.getState().setWorktreeMetadata(sessionId, null)
 }
@@ -1252,7 +1315,14 @@ export type ArchiveSessionsOptions = {
 }
 
 /**
- * Archive several sessions sequentially, preserving partial results.
+ * Archive several sessions, preserving partial results.
+ *
+ * Sessions that carry no review or btw link are archived by their directory's
+ * server in one request, and the whole answer is reconciled with a single store
+ * write. The remainder — review sessions, btw forks, sessions with an active
+ * btw fork, and any session this client does not hold — keep the per-session
+ * path, because unlinking a partner is UI-owned work that reads and rewrites
+ * another session's metadata.
  *
  * One failed session never blocks or erases the others: it is reported in
  * `failedIds` while the remaining IDs are still attempted. When
@@ -1269,10 +1339,55 @@ export async function archiveSessions(
   const archivedIds: string[] = []
   const failedIds: string[] = []
   const expectedRuntimeKey = options?.expectedRuntimeKey ?? getRuntimeKey()
+  if (ids.length === 0) return { archivedIds, failedIds }
 
-  for (const [index, id] of ids.entries()) {
+  const plan = planArchiveBatches(ids)
+
+  for (const [directory, batchIds] of plan.batchesByDirectory) {
     if (isStaleRuntime(expectedRuntimeKey)) {
-      failedIds.push(...ids.slice(index))
+      failedIds.push(...batchIds)
+      continue
+    }
+
+    const archivedAt = Date.now()
+    registerBulkArchiveEchoes(
+      expectedRuntimeKey,
+      batchIds.map((id) => ({ id, archivedAt })),
+    )
+    const result = await requestSessionArchiveBatch(directory, batchIds, archivedAt)
+    if (isStaleRuntime(expectedRuntimeKey)) {
+      failedIds.push(...batchIds)
+      continue
+    }
+
+    if (result.outcome === "archived") {
+      releaseBulkArchiveEchoes(expectedRuntimeKey, batchIds)
+      registerBulkArchiveEchoes(
+        expectedRuntimeKey,
+        result.archived.flatMap((session) => (
+          session.time?.archived === undefined
+            ? []
+            : [{ id: session.id, archivedAt: session.time.archived }]
+        )),
+      )
+      commitArchivedSessions(result.archived, directory)
+      archivedIds.push(...result.archived.map((session) => session.id))
+      failedIds.push(...result.failedIds)
+      continue
+    }
+
+    // The runtime does not serve the batch route, or its answer could not be
+    // trusted. Archiving each session individually is slower but reaches the
+    // same state, and re-archiving a session the server already archived writes
+    // the same field again.
+    console.warn("[session-actions] archive batch unavailable, archiving one by one", result.reason)
+    releaseBulkArchiveEchoes(expectedRuntimeKey, batchIds)
+    plan.individualIds.push(...batchIds)
+  }
+
+  for (const [index, id] of plan.individualIds.entries()) {
+    if (isStaleRuntime(expectedRuntimeKey)) {
+      failedIds.push(...plan.individualIds.slice(index))
       break
     }
     if (await archiveSession(id, expectedRuntimeKey)) archivedIds.push(id)
@@ -1282,6 +1397,82 @@ export async function archiveSessions(
   return { archivedIds, failedIds }
 }
 
+/**
+ * A session whose archive also has to rewrite another session's metadata.
+ *
+ * Review sessions and btw forks point at a parent that must be unlinked, and a
+ * parent with an active btw fork has to delete that fork. Those are
+ * read-modify-write pairs on a second session, so they stay on the per-session
+ * path instead of the server batch.
+ */
+function hasLinkedSessionCleanup(session: Session): boolean {
+  return isReviewSession(session) || isBtwSession(session) || Boolean(getBtwSessionID(session))
+}
+
+/**
+ * Split the requested IDs into per-directory server batches and the sessions
+ * that must be archived individually.
+ *
+ * Link classification reads this client's session records rather than
+ * refetching each session: those records are kept current by the same
+ * `session.updated` events that publish a link created anywhere else, so a
+ * fetch per session would buy no authority the store does not already have.
+ * A session this client does not hold is classified as individual, which
+ * restores the per-session fetch for exactly the cases where the store has
+ * nothing to say.
+ */
+function planArchiveBatches(ids: string[]) {
+  const global = useGlobalSessionsStore.getState()
+  const knownSessions = new Map<string, Session>()
+  for (const session of [...global.activeSessions, ...global.archivedSessions]) {
+    knownSessions.set(session.id, session)
+  }
+  for (const store of _childStores?.children.values() ?? []) {
+    for (const session of store.getState().session) knownSessions.set(session.id, session)
+  }
+
+  const batchesByDirectory = new Map<string, string[]>()
+  const individualIds: string[] = []
+
+  for (const id of ids) {
+    const session = knownSessions.get(id)
+    const directory = session
+      ? resolveGlobalSessionDirectory(session) ?? getSessionDirectory(id)
+      : undefined
+    if (!session || !directory || hasLinkedSessionCleanup(session)) {
+      individualIds.push(id)
+      continue
+    }
+    const batch = batchesByDirectory.get(directory)
+    if (batch) batch.push(id)
+    else batchesByDirectory.set(directory, [id])
+  }
+
+  return { batchesByDirectory, individualIds }
+}
+
+/**
+ * Reconcile a server-confirmed archive batch with one write per store.
+ *
+ * This mirrors what `archiveSession` does for a single session — drop it from
+ * the live directory stores, invalidate its cached messages, move it to the
+ * archived bucket, and clear it if it was open — with the per-session store
+ * notifications collapsed into one.
+ */
+function commitArchivedSessions(sessions: Session[], directory: string): void {
+  if (sessions.length === 0) return
+
+  const ids = sessions.map((session) => session.id)
+  const snapshots = removeSessionsFromLiveStores(ids, directory)
+  const directories = [...snapshots.map((snapshot) => snapshot.directory), directory]
+  for (const id of ids) invalidateSessionLoads(id, directories)
+
+  useGlobalSessionsStore.getState().upsertSessions(sessions)
+
+  const ui = useSessionUIStore.getState()
+  if (ui.currentSessionId && ids.includes(ui.currentSessionId)) ui.setCurrentSession(null)
+}
+
 /**
  * Sentinel written to `time.archived` when restoring a session.
  *

packages/ui/src/sync/session-archive-batch.ts

@@ -0,0 +1,77 @@
+/**
+ * Server-side archive batch.
+ *
+ * Archiving the sessions linked to a worktree one request at a time is what
+ * made removing a worktree with many sessions take tens of seconds: every
+ * session cost its own round trip and its own store reconciliation. This asks
+ * the OpenChamber server to archive the whole batch next to OpenCode, so the
+ * browser spends one request and reconciles once.
+ *
+ * The route is an OpenChamber capability, not an OpenCode one. Runtimes that do
+ * not serve it (the VS Code webview has no server process) answer with a stable
+ * unsupported status, and callers fall back to archiving session by session.
+ */
+
+import type { Session } from '@opencode-ai/sdk/v2/client';
+import { z } from 'zod';
+
+import { runtimeFetch } from '@/lib/runtime-fetch';
+
+/**
+ * The route answers with sessions OpenCode itself returned from
+ * `session.update`. Only the identity this layer routes on is asserted here;
+ * every other field is carried through to the stores exactly as the server
+ * sent it, the same as for any other session response.
+ */
+const archiveResponseSchema = z.object({
+  archived: z.array(z.looseObject({ id: z.string().min(1) })),
+  failedIds: z.array(z.string().min(1)),
+});
+
+export type SessionArchiveBatchResult =
+  | { outcome: 'archived'; archived: Session[]; failedIds: string[] }
+  | { outcome: 'unavailable'; reason: string };
+
+export async function requestSessionArchiveBatch(
+  directory: string,
+  ids: string[],
+  archivedAt: number,
+): Promise<SessionArchiveBatchResult> {
+  let response: Response;
+  try {
+    response = await runtimeFetch('/api/openchamber/sessions/archive', {
+      method: 'POST',
+      headers: { 'content-type': 'application/json' },
+      body: JSON.stringify({ directory, ids, archivedAt }),
+    });
+  } catch (error) {
+    return { outcome: 'unavailable', reason: error instanceof Error ? error.message : 'archive request failed' };
+  }
+
+  if (!response.ok) {
+    return { outcome: 'unavailable', reason: `archive request failed with ${response.status}` };
+  }
+
+  let body: unknown;
+  try {
+    body = await response.json();
+  } catch (error) {
+    return { outcome: 'unavailable', reason: error instanceof Error ? error.message : 'archive response was not JSON' };
+  }
+
+  const parsed = archiveResponseSchema.safeParse(body);
+  if (!parsed.success) {
+    // A body this layer cannot read is reported as unavailable rather than as
+    // an empty success, so a caller never mistakes "the response made no
+    // sense" for "nothing needed archiving" and drops the sessions.
+    return { outcome: 'unavailable', reason: `malformed archive response: ${parsed.error.issues[0]?.message ?? 'unknown shape'}` };
+  }
+
+  return {
+    outcome: 'archived',
+    // SAFETY: the schema guarantees the non-empty string `id` this layer keys
+    // on; the remaining fields are the server's own session payload.
+    archived: parsed.data.archived as Session[],
+    failedIds: parsed.data.failedIds,
+  };
+}

packages/ui/src/sync/sync-context.tsx

@@ -38,7 +38,11 @@ import { setSyncRefs, getAllSyncSessions } from "./sync-refs"
 import { useSessionUIStore } from "./session-ui-store"
 import { stripSessionDiffSnapshots } from "./sanitize"
 import { upsertSessionRecord } from "./session-records"
-import { applySessionEventToGlobalSessions, applySessionEventsToGlobalSessions } from "./session-event-router"
+import {
+  applySessionEventToGlobalSessions,
+  applySessionEventsToGlobalSessions,
+} from "./session-event-router"
+import { shouldConsumeBulkArchiveEcho } from "./bulk-archive-echo"
 import { syncDebug } from "./debug"
 import { getReconnectCandidateSessionIds, mergeBootstrapSessions } from "./reconnect-recovery"
 import { messagesBefore } from "./message-ordering"
@@ -1586,6 +1590,8 @@ export function handleEvent(
     return
   }
 
+  if (shouldConsumeBulkArchiveEcho(payload, expectedRuntimeKey)) return
+
   const directory = resolveDirectoryFromRoutingIndex(routingIndex, rawDirectory, payload, childStores, batch)
 
   if (payload.type === "session.deleted" && expectedRuntimeKey === getRuntimeKey()) {