perf: overhaul session loading, caching, and runtime isolation (#2360)

Improve OpenChamber responsiveness under large session workloads while fixing
cache, synchronization, and persistence correctness across runtimes, projects,
directories, and worktrees.

- prioritize selected and visible sessions during bootstrap and defer
  non-critical enrichment work
- reduce redundant message loading, event processing, store publication, and
  hidden sidebar work
- prevent stale session and message requests from overwriting newer
  authoritative state
- preserve existing data when authoritative fetches fail instead of treating
  failures as successful empty responses
- scope session materialization, messages, drafts, queues, todos, pins,
  permissions, folders, tabs, Git state, and pull request data by runtime and
  directory identity
- harden runtime switching, reconnect, cleanup, mutation reconciliation, and
  persisted-state ordering
- preserve live subagent Task linkage when metadata arrives after an older
  message request or while streaming parts are suspended
- coalesce overlapping tail refreshes without losing newer refresh demand
- improve cold-session loading by moving deferrable work out of the critical
  bootstrap path
- isolate URL authentication, mobile credentials, native secrets, and other
  runtime-owned state across endpoint changes
- bound long-lived caches and remove avoidable allocations from event and
  rendering hot paths
- limit virtualization to archive collections where it improves rendering
  without disrupting active sidebar layout
- stabilize session folders, pin ordering, expanded state, and persisted
  sidebar behavior
- open skill files through the same secure editor and outside-workspace grant
  flow used by file navigation, including worktree sessions
- expand regression coverage for stale completions, runtime collisions,
  reconnect behavior, persistence races, authoritative empty results, and
  subagent refresh ordering
- document the updated synchronization, cache ownership, performance, and
  runtime-isolation invariants

packages/ui/src/contexts/ThemeSystemContext.tsx

@@ -2,6 +2,7 @@ import React, {
   useEffect,
   useMemo,
   useCallback,
+  useRef,
   useState,
 } from 'react';
 import { flushSync } from 'react-dom';
@@ -24,6 +25,7 @@ import { runtimeFetch } from '@/lib/runtime-fetch';
 import { getInitialSystemPreference, readEmbeddedThemeSearchParams } from './theme-embedded-bootstrap';
 import { isValidTheme } from './theme-validation';
 import { getSyncedThemeFromPayload, getSyncedThemeVariant } from './theme-sync-payload';
+import { getRuntimeKey, subscribeRuntimeEndpointChanged } from '@/lib/runtime-switch';
 
 type ThemePreferences = {
   themeMode: ThemeMode;
@@ -172,8 +174,8 @@ export function ThemeSystemProvider({ children, defaultThemeId }: ThemeSystemPro
     return existing || null;
   });
   const isVSCode = useMemo(() => isVSCodeRuntime(), []);
-  const isLocalDesktopOrigin = useMemo(() => isDesktopLocalOriginActive(), []);
   const isDesktopShell = useMemo(() => detectDesktopShell(), []);
+  const customThemesRequestRef = useRef(0);
   const receivesParentThemeSync = useMemo(() => {
     if (typeof window === 'undefined') {
       return false;
@@ -249,11 +251,13 @@ export function ThemeSystemProvider({ children, defaultThemeId }: ThemeSystemPro
       return;
     }
 
+    const runtimeKey = getRuntimeKey();
+    const request = ++customThemesRequestRef.current;
     setCustomThemesLoading(true);
     try {
       const res = await runtimeFetch('/api/config/themes', {
         method: 'GET',
-        credentials: isLocalDesktopOrigin ? 'omit' : 'include',
+        credentials: isDesktopLocalOriginActive() ? 'omit' : 'include',
         headers: {
           Accept: 'application/json',
         },
@@ -269,20 +273,31 @@ export function ThemeSystemProvider({ children, defaultThemeId }: ThemeSystemPro
       }
 
       const payload = await res.json();
+      if (request !== customThemesRequestRef.current || runtimeKey !== getRuntimeKey()) return;
       const incoming = Array.isArray(payload?.themes) ? payload.themes : [];
       const normalized = incoming.filter(isValidTheme);
       setCustomThemes(normalized);
     } catch {
       // ignore
     } finally {
-      setCustomThemesLoading(false);
+      if (request === customThemesRequestRef.current && runtimeKey === getRuntimeKey()) {
+        setCustomThemesLoading(false);
+      }
     }
-  }, [isLocalDesktopOrigin, isVSCode]);
+  }, [isVSCode]);
 
   useEffect(() => {
     void reloadCustomThemes();
   }, [reloadCustomThemes]);
 
+  useEffect(() => subscribeRuntimeEndpointChanged((detail) => {
+    if (detail.runtimeKey === detail.previousRuntimeKey || isVSCode) return;
+    customThemesRequestRef.current += 1;
+    setCustomThemes([]);
+    setCustomThemesLoading(false);
+    void reloadCustomThemes();
+  }), [isVSCode, reloadCustomThemes]);
+
   useEffect(() => {
     if (!isVSCode) {
       return;