perf(chat): make session switching feel instant

Switching sessions ran as one synchronous commit: sidebar highlight, URL,
a full timeline remount with markdown re-parse, and around nine requests,
so nothing changed on screen for 150-250ms after the click.

- ChatContainer swaps the timeline on a deferred copy of the selection, so
  the active row, URL, and tab commit first and the timeline renders behind
  them; selection policy keeps reading the live store value.
- The message fetch starts before the selection is published.
- Sidebar rows stop re-rendering on a project switch: directory-scoped sync
  hooks read the runtime context and a subscribable current-directory source
  instead of the directory-bearing context; the grouping builder reads git
  branches through a ref and section caches key the branches they use;
  descendant ids are keyed by content. Rows per switch went from 73 to 8.
- Markdown skips the async re-render when the settled cached blocks are
  already painted, and mounts synchronously once its lazy module is loaded;
  the module is preloaded at boot.
- A timeline reveal gate holds a freshly opened session at opacity 0 while
  any provisional markdown paint catches up (250ms cap), then fades the whole
  timeline in once, so text, tools, and recap appear together.
- Switch fan-out trimmed: knowledge summary deduped, MCP status refreshed only
  when stale, non-repo directories cached by the git repo check, OpenChamber
  defaults cached briefly, agent memory reused for the same project, goal
  text cached, PWA manifest rebuilt after the switch settles.
- Header tabs snap into the active state and keep the title at the same
  height in both states.
- Prefetch on row press; composer focus moved off the commit.

`bun run profile:switch` records ack/content latency, longest task, and
requests per switch, cold and warm, and compares runs against a baseline.
Measured warm switch: ack 228ms to about 40-60ms, content 228ms to about
100-120ms.
This commit is contained in:
Bohdan Triapitsyn
2026-08-29 17:01:15 +03:00
parent 123c14260a
commit edfc9779cf
32 changed files with 947 additions and 118 deletions
@@ -11,6 +11,7 @@ import { Skeleton } from '@/components/ui/skeleton';
import ChatEmptyState from './ChatEmptyState';
import { useGlobalSyncStore } from '@/sync/global-sync-store';
import MessageList, { type MessageListHandle } from './MessageList';
import { createTimelineRevealGate, TIMELINE_REVEAL_CAP_MS, TimelineRevealGateContext } from './timelineRevealGate';
import { PermissionCard } from './PermissionCard';
import { QuestionCard } from './QuestionCard';
import { hasActiveQuestionToolInCurrentTurn, recoverPendingQuestionWithRetry } from '@/sync/question-recovery';
@@ -175,9 +176,6 @@ type ChatViewportProps = {
} | null;
scrollToBottom: () => void;
endPinningReleased: boolean;
// One-shot fade for content that replaced the hydration skeleton;
// cached sessions render instantly without it.
revealContent: boolean;
sessionQuestions: QuestionRequest[];
sessionPermissions: PermissionRequest[];
isProgrammaticFollowActive: boolean;
@@ -214,7 +212,6 @@ const ChatViewport = React.memo(({
retryOverlay,
scrollToBottom,
endPinningReleased,
revealContent,
sessionQuestions,
sessionPermissions,
isProgrammaticFollowActive,
@@ -368,6 +365,45 @@ const ChatViewport = React.memo(({
</>
), [currentSessionId, directory, isMobile, sessionPermissions, sessionQuestions]);
// Opening a session paints the timeline as one finished picture: the root
// stays invisible while any renderer holds a provisional first paint, then
// everything appears together. A warm switch, where nothing is held,
// reveals in the same frame; a cold open fades in once as a whole.
const timelineRootRef = React.useRef<HTMLDivElement | null>(null);
const revealGate = React.useMemo(() => createTimelineRevealGate(), [currentSessionKey]);
React.useLayoutEffect(() => {
const root = timelineRootRef.current;
if (!root) return;
root.setAttribute('data-timeline-reveal', 'pending');
let finished = false;
let timer: number | null = null;
const reveal = (fade: boolean) => {
if (finished) return;
finished = true;
if (timer !== null) window.clearTimeout(timer);
if (fade) root.setAttribute('data-timeline-reveal', 'fading');
else root.removeAttribute('data-timeline-reveal');
};
// Holds are taken in layout effects, including those of rows the list
// mounts in a nested synchronous pass; a microtask runs after all of
// them and still before the browser paints this commit.
queueMicrotask(() => {
if (finished) return;
revealGate.close();
if (revealGate.holds === 0) {
reveal(false);
return;
}
revealGate.onEmpty = () => reveal(true);
timer = window.setTimeout(() => reveal(true), TIMELINE_REVEAL_CAP_MS);
});
return () => {
finished = true;
if (timer !== null) window.clearTimeout(timer);
revealGate.onEmpty = null;
};
}, [revealGate]);
const scrollContainerProps = React.useMemo(() => ({
className: 'absolute inset-0 overflow-y-auto overflow-x-hidden z-0 chat-scroll overlay-scrollbar-target',
style: CHAT_SCROLL_STYLE,
@@ -385,11 +421,12 @@ const ChatViewport = React.memo(({
isDesktopExpandedInput
? 'absolute inset-0 opacity-0 pointer-events-none'
: 'flex-1',
revealContent && !isDesktopExpandedInput && 'oc-chat-hydration-reveal',
)}
ref={timelineRootRef}
aria-hidden={isDesktopExpandedInput}
>
<div className="absolute inset-0">
<TimelineRevealGateContext.Provider value={revealGate}>
<MessageList
key={currentSessionKey}
ref={messageListRef}
@@ -417,6 +454,7 @@ const ChatViewport = React.memo(({
listFooter={listFooter}
scrollContainerProps={scrollContainerProps}
/>
</TimelineRevealGateContext.Provider>
<OverlayScrollbar containerRef={scrollRef} disableHorizontal suppressVisibility={isProgrammaticFollowActive} userIntentOnly observeMutations={false} />
{showPromptNavigator && promptTurnIds.length >= 2 ? (
<PromptNavigatorRail
@@ -448,7 +486,6 @@ const ChatViewport = React.memo(({
&& prev.retryOverlay === next.retryOverlay
&& prev.scrollToBottom === next.scrollToBottom
&& prev.endPinningReleased === next.endPinningReleased
&& prev.revealContent === next.revealContent
&& prev.sessionQuestions === next.sessionQuestions
&& prev.sessionPermissions === next.sessionPermissions
&& prev.isProgrammaticFollowActive === next.isProgrammaticFollowActive
@@ -824,9 +861,6 @@ export const ChatContainer: React.FC<ChatContainerProps> = ({
return () => setWorkStatusPanelVisible(false);
}, [setWorkStatusPanelVisible, showWorkStatusPanel]);
const messageListRef = React.useRef<MessageListHandle | null>(null);
// Session keys that showed the hydration skeleton this app run; their
// content gets a one-shot reveal fade once it replaces the skeleton.
const hydrationRevealKeyRef = React.useRef<string | null>(null);
const currentSession = useSession(currentSessionId, effectiveSessionDirectory);
const parentSession = useParentSession(currentSessionId, effectiveSessionDirectory);
@@ -1163,15 +1197,6 @@ export const ChatContainer: React.FC<ChatContainerProps> = ({
const isSessionHydrating =
Boolean(currentSessionId)
&& !hasRenderableSessionSnapshot;
React.useEffect(() => {
if (isSessionHydrating || hydrationRevealKeyRef.current === null) return;
// One-shot: forget the key after the reveal animation has played so a
// later (now cached) visit to the same session opens instantly.
const timer = setTimeout(() => {
hydrationRevealKeyRef.current = null;
}, 400);
return () => clearTimeout(timer);
}, [isSessionHydrating, currentSessionKey]);
const retrySessionLoad = React.useCallback(() => {
if (!messagesEnabled || !currentSessionId) return;
void sync.ensureSessionRenderable(currentSessionId, true, effectiveSessionDirectory);
@@ -1310,9 +1335,6 @@ export const ChatContainer: React.FC<ChatContainerProps> = ({
}
const showHydrationSkeleton = isSessionHydrating && sessionMessages.length === 0 && !sessionIsWorking;
if (showHydrationSkeleton) {
hydrationRevealKeyRef.current = currentSessionKey ?? currentSessionId ?? null;
}
if (showHydrationSkeleton) {
if (sessionMessageLoadState.status === 'error') {
return (
@@ -1415,7 +1437,6 @@ export const ChatContainer: React.FC<ChatContainerProps> = ({
retryOverlay={retryOverlay}
scrollToBottom={resumeToLatestInstant}
endPinningReleased={userOwnsScroll}
revealContent={hydrationRevealKeyRef.current !== null && hydrationRevealKeyRef.current === (currentSessionKey ?? currentSessionId ?? null)}
sessionQuestions={sessionQuestions}
sessionPermissions={sessionPermissions}
isProgrammaticFollowActive={isFollowingProgrammatically}
+13 -9
View File
@@ -72,8 +72,8 @@ import { useChatSearchDirectory } from '@/hooks/useChatSearchDirectory';
import { opencodeClient } from '@/lib/opencode/client';
import { useGitStore, useIsGitRepo } from '@/stores/useGitStore';
import { useDirectoryStore } from '@/stores/useDirectoryStore';
import { useSkillsStore } from '@/stores/useSkillsStore';
import { useCommandsStore } from '@/stores/useCommandsStore';
import { selectSkillsForDirectory, useSkillsStore } from '@/stores/useSkillsStore';
import { selectCommandsForDirectory, useCommandsStore } from '@/stores/useCommandsStore';
import { useRuntimeAPIs } from '@/hooks/useRuntimeAPIs';
import { useEffectiveDirectory } from '@/hooks/useEffectiveDirectory';
import { usePermissionStore } from '@/stores/permissionStore';
@@ -602,8 +602,8 @@ const ChatInputComponent: React.FC<ChatInputProps> = ({
// Known slash-invocations (commands + skills + built-ins) used to highlight
// matching /tokens in the composer, the same way confirmed @files are.
const availableCommands = useCommandsStore((s) => s.commands);
const availableSkills = useSkillsStore((s) => s.skills);
const availableCommands = useCommandsStore((s) => selectCommandsForDirectory(s, currentDirectory));
const availableSkills = useSkillsStore((s) => selectSkillsForDirectory(s, currentDirectory));
const knownSlashNames = React.useMemo(() => {
const names = new Set<string>([
'init', 'review', 'undo', 'redo', 'timeline', 'compact', 'btw', 'summary', 'workspace-review', 'plan-feature', 'craft-goal', 'schedule-task', 'catch-up', 'debug', 'weigh', 'explore',
@@ -1140,7 +1140,7 @@ const ChatInputComponent: React.FC<ChatInputProps> = ({
: [];
const availableSkillNames = new Set(
useSkillsStore.getState().skills.map((skill) => skill.name),
selectSkillsForDirectory(useSkillsStore.getState(), currentDirectory).map((skill) => skill.name),
);
const outgoing = buildOutgoingMessage({
@@ -2262,10 +2262,14 @@ const ChatInputComponent: React.FC<ChatInputProps> = ({
};
React.useEffect(() => {
if (active && currentSessionId && composerRef.current && !isMobile) {
composerRef.current.focus();
}
if (!active || !currentSessionId || isMobile) return;
// Focusing forces layout. Right after a session switch the layout is
// dirty from the whole timeline mounting, so the focus call would pay
// for that layout inside the commit; a frame later it is nearly free.
const frame = window.requestAnimationFrame(() => {
composerRef.current?.focus();
});
return () => window.cancelAnimationFrame(frame);
}, [active, currentSessionId, isMobile]);
React.useEffect(() => {
@@ -2,7 +2,7 @@ import React from 'react';
import { lazyWithChunkRecovery } from '@/lib/chunkLoadRecovery';
import { isMobileSurfaceRuntime } from '@/lib/runtimeSurface';
import { cn } from '@/lib/utils';
import { loadMarkdownRendererModule } from './markdownRendererLoader';
import { getLoadedMarkdownRendererModule, loadMarkdownRendererModule } from './markdownRendererLoader';
// Thin lazy wrapper around the MarkdownRenderer implementation.
// The full implementation (marked + Shiki highlighting + KaTeX + morphdom
@@ -41,21 +41,29 @@ const MobileMarkdownFallback = (props: { content?: unknown; className?: unknown;
);
};
export const MarkdownRenderer: React.FC<React.ComponentPropsWithoutRef<typeof MarkdownRendererLazy>> = (props) => (
<React.Suspense fallback={<MobileMarkdownFallback {...props} />}>
<MarkdownRendererLazy {...props} />
</React.Suspense>
);
export const MarkdownRenderer: React.FC<React.ComponentPropsWithoutRef<typeof MarkdownRendererLazy>> = (props) => {
const loaded = getLoadedMarkdownRendererModule();
if (loaded) return <loaded.MarkdownRenderer {...props} />;
return (
<React.Suspense fallback={<MobileMarkdownFallback {...props} />}>
<MarkdownRendererLazy {...props} />
</React.Suspense>
);
};
type SimpleMarkdownRendererProps = React.ComponentPropsWithoutRef<typeof SimpleMarkdownRendererLazy> & {
fallbackContent?: React.ReactNode;
};
export const SimpleMarkdownRenderer: React.FC<SimpleMarkdownRendererProps> = ({ fallbackContent, ...props }) => (
<React.Suspense fallback={fallbackContent ?? <MobileMarkdownFallback {...props} />}>
<SimpleMarkdownRendererLazy {...props} />
</React.Suspense>
);
export const SimpleMarkdownRenderer: React.FC<SimpleMarkdownRendererProps> = ({ fallbackContent, ...props }) => {
const loaded = getLoadedMarkdownRendererModule();
if (loaded) return <loaded.SimpleMarkdownRenderer {...props} />;
return (
<React.Suspense fallback={fallbackContent ?? <MobileMarkdownFallback {...props} />}>
<SimpleMarkdownRendererLazy {...props} />
</React.Suspense>
);
};
export const MarkdownImageGallery: React.FC<React.ComponentPropsWithoutRef<typeof MarkdownImageGalleryLazy>> = (props) => (
<React.Suspense fallback={null}>
@@ -193,6 +193,8 @@ const fakeReact = {
return hookStates[index] as { current: T };
},
memo: <T>(component: T): T => component,
createContext: <T>(defaultValue: T) => ({ Provider: 'provider', defaultValue }),
useContext: <T>(context: { defaultValue: T }): T => context.defaultValue,
};
const fakeJsx = (_type: string, props: FakeJsxProps | null, ...children: FakeElement[]): FakeElement => {
@@ -51,6 +51,7 @@ import {
import { fileReferenceExists } from './fileReferenceStat';
import { streamPerfCount, streamPerfObserve } from '@/stores/utils/streamDebug';
import { detachedMarkdownDomCache, type DetachedMarkdownDomKey } from './markdown/detachedMarkdownDomCache';
import { TimelineRevealGateContext } from './timelineRevealGate';
import { getRuntimeKey } from '@/lib/runtime-switch';
const useCurrentMermaidTheme = () => {
@@ -692,6 +693,30 @@ const useMermaidInlineInteractions = ({
const MERMAID_RENDER_CACHE = new Map<string, MermaidRender>();
const MERMAID_RENDER_CACHE_MAX = 100;
const MARKDOWN_DECORATION_ID_ATTR = 'data-md-decoration-id';
// True when the container already holds exactly these settled blocks with the
// current decoration. The first paint of a remounted message is served from
// the block cache; when that paint is already final, the async render would
// only parse, highlight, sanitize, and morph the same HTML into place again.
const domMatchesRenderedBlocks = (
target: HTMLElement,
blocks: ReadonlyArray<{ id: string }>,
decorationId: string,
): boolean => {
const children = target.children;
if (children.length !== blocks.length) return false;
for (let index = 0; index < blocks.length; index += 1) {
const child = children[index];
if (
!child
|| child.getAttribute('data-md-id') !== blocks[index]?.id
|| child.getAttribute(MARKDOWN_DECORATION_ID_ATTR) !== decorationId
) {
return false;
}
}
return true;
};
const MARKDOWN_DECORATION_IDS = new WeakMap<DecorateContext, string>();
let nextMarkdownDecorationId = 0;
const MARKDOWN_DOM_CACHE_MAX_SOURCE_CHARS = 200_000;
@@ -804,6 +829,16 @@ const useMorphdomMarkdown = ({
const mermaidViewerRef = React.useRef<ReturnType<typeof createMermaidViewerRegistry> | null>(null);
const renderRevisionRef = React.useRef(0);
// A provisional first paint (blocks not in the settled cache) holds the
// timeline reveal until the async render lands, so the session opens with
// final code highlighting instead of a visible restyle.
const revealGate = React.useContext(TimelineRevealGateContext);
const releaseRevealHoldRef = React.useRef<(() => void) | null>(null);
const releaseRevealHold = React.useCallback(() => {
releaseRevealHoldRef.current?.();
releaseRevealHoldRef.current = null;
}, []);
React.useEffect(() => releaseRevealHold, [releaseRevealHold]);
// Only DOM that was actually restored or completed by the async pipeline is
// eligible for capture. A fallback from an earlier content revision is not.
const mountedDomRef = React.useRef<{
@@ -909,6 +944,9 @@ const useMorphdomMarkdown = ({
}
if (hasMermaidBlock) refreshMermaidViewers();
} else {
if (!streaming && !releaseRevealHoldRef.current) {
releaseRevealHoldRef.current = revealGate?.hold() ?? null;
}
const block = document.createElement('div');
block.setAttribute('data-md-block', '');
block.style.display = 'contents';
@@ -939,6 +977,18 @@ const useMorphdomMarkdown = ({
const renderRevision = renderRevisionRef.current;
const decorationId = getMarkdownDecorationId(ctx);
if (!streaming) {
const cachedBlocks = getCachedMarkdownBlocks(text, imageMode);
if (cachedBlocks && domMatchesRenderedBlocks(target, cachedBlocks, decorationId)) {
mountedDomRef.current = domCacheKey
? { key: domCacheKey, copiedLabel: ctx.labels.copied }
: null;
streamPerfCount('ui.markdown_renderer.settled_paint.reused');
releaseRevealHold();
return;
}
}
void renderMarkdownBlocks(text, streaming, imageMode).then((blocks) => {
if (!active || renderRevisionRef.current !== renderRevision) return;
const existing = Array.from(target.children) as HTMLElement[];
@@ -1028,12 +1078,13 @@ const useMorphdomMarkdown = ({
mountedDomRef.current = domCacheKey
? { key: domCacheKey, copiedLabel: ctx.labels.copied }
: null;
releaseRevealHold();
});
return () => {
active = false;
};
}, [containerRef, ctx, domCacheKey, imageMode, refreshMermaidViewers, streaming, text]);
}, [containerRef, ctx, domCacheKey, imageMode, refreshMermaidViewers, releaseRevealHold, streaming, text]);
React.useEffect(() => {
const container = containerRef.current;
@@ -1,13 +1,31 @@
let markdownRendererModulePromise: Promise<typeof import('./MarkdownRendererImpl')> | null = null;
type MarkdownRendererModule = typeof import('./MarkdownRendererImpl');
let markdownRendererModulePromise: Promise<MarkdownRendererModule> | null = null;
let markdownRendererModule: MarkdownRendererModule | null = null;
export const loadMarkdownRendererModule = () => {
markdownRendererModulePromise ??= import('./MarkdownRendererImpl').catch((error) => {
markdownRendererModulePromise = null;
throw error;
});
markdownRendererModulePromise ??= import('./MarkdownRendererImpl')
.then((module) => {
markdownRendererModule = module;
return module;
})
.catch((error) => {
markdownRendererModulePromise = null;
throw error;
});
return markdownRendererModulePromise;
};
/**
* The module once it has loaded, so a renderer can mount synchronously instead
* of suspending. A lazy component that suspends even on an already-resolved
* promise shows its fallback for a tick, and React then throttles the reveal
* of every boundary that resolves in the following ~300ms, which is how a
* freshly opened session showed user text first and assistant text a third of
* a second later.
*/
export const getLoadedMarkdownRendererModule = () => markdownRendererModule;
export const preloadMarkdownRenderer = () => {
void loadMarkdownRendererModule().catch(() => undefined);
};
@@ -0,0 +1,54 @@
import React from 'react';
/**
* Coordinates the first paint of a freshly opened session so the timeline
* appears as one finished picture instead of arriving in pieces.
*
* Renderers that mount with a provisional paint (markdown whose blocks are not
* in the settled cache yet, so code is unhighlighted) take a hold while they
* catch up. The timeline stays invisible while any hold is open, then reveals
* everything at once. The gate accepts holds only during the opening commit:
* rows that mount later, while scrolling, must never hide the timeline.
*
* A hold that never releases must not hide the chat forever, so the owner
* reveals after `TIMELINE_REVEAL_CAP_MS` regardless.
*/
type TimelineRevealGate = {
/** Take a hold; returns the release. Returns null once the gate is closed. */
hold: () => (() => void) | null;
/** Stops accepting holds. Existing holds still count. */
close: () => void;
readonly holds: number;
/** Called when the last hold releases, if the gate is closed by then. */
onEmpty: (() => void) | null;
};
export const TIMELINE_REVEAL_CAP_MS = 250;
export const createTimelineRevealGate = (): TimelineRevealGate => {
let holds = 0;
let accepting = true;
const gate: TimelineRevealGate = {
hold: () => {
if (!accepting) return null;
holds += 1;
let released = false;
return () => {
if (released) return;
released = true;
holds -= 1;
if (holds === 0 && !accepting) gate.onEmpty?.();
};
},
close: () => {
accepting = false;
},
get holds() {
return holds;
},
onEmpty: null,
};
return gate;
};
export const TimelineRevealGateContext = React.createContext<TimelineRevealGate | null>(null);
@@ -13,6 +13,8 @@ type Props = {
directory: string | null;
};
const MCP_STATUS_MAX_AGE_MS = 60_000;
/**
* MCP servers with their connection switches, reusing the dropdown's own
* connect/disconnect actions.
@@ -23,17 +25,19 @@ export const WorkStatusMcpSection: React.FC<Props> = ({ directory }) => {
const mcpStatus = useMcpStore(
React.useCallback((state) => state.getStatusForDirectory(directory), [directory]),
);
const refreshMcp = useMcpStore((state) => state.refresh);
const ensureMcpFresh = useMcpStore((state) => state.ensureFresh);
const connect = useMcpStore((state) => state.connect);
const disconnect = useMcpStore((state) => state.disconnect);
const [busyServer, setBusyServer] = React.useState<string | null>(null);
// The panel must not depend on the header dropdown having been mounted or
// opened to know its MCP servers. Silent and background-gated, so it cannot
// compete with chat bootstrap traffic for sockets.
// compete with chat bootstrap traffic for sockets. The section remounts on
// every session switch, so it only asks for a status that is missing or
// older than a minute; connect/disconnect/auth refresh on their own.
React.useEffect(() => {
void runBackgroundNetworkTask(() => refreshMcp({ directory, silent: true }));
}, [directory, refreshMcp]);
void runBackgroundNetworkTask(() => ensureMcpFresh({ directory, silent: true, maxAgeMs: MCP_STATUS_MAX_AGE_MS }));
}, [directory, ensureMcpFresh]);
const mcpServers = React.useMemo(
() => Object.entries(mcpStatus ?? {}).sort(([left], [right]) => left.localeCompare(right)),