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/components/layout/MainLayout.tsx

@@ -72,7 +72,6 @@ export const MainLayout: React.FC = () => {
         setMobileLeftDrawerOpen(open);
         useUIStore.getState().setSessionSwitcherOpen(open);
     }, []);
-    const mobileRightDrawerOpenRef = React.useRef(false);
     const initialDrawerWidthRef = React.useRef(typeof window === 'undefined' ? 0 : window.innerWidth);
 
     // Left drawer motion value
@@ -114,7 +113,6 @@ export const MainLayout: React.FC = () => {
             setMobileRightDrawerVisible(false);
             return;
         }
-        mobileRightDrawerOpenRef.current = mobileRightSidebarOpen;
         if (mobileRightSidebarOpen) {
             setMobileRightDrawerVisible(true);
         }
@@ -441,7 +439,7 @@ export const MainLayout: React.FC = () => {
                     >
                         <main className="w-full h-full overflow-hidden bg-background relative" data-page-scroll-lock="true">
                             <div className={cn('absolute inset-0', !isChatActive && 'invisible')}>
-                                <ErrorBoundary><ChatView /></ErrorBoundary>
+                                <ErrorBoundary><ChatView active={isChatActive && !isSettingsDialogOpen} /></ErrorBoundary>
                             </div>
                             {secondaryView && (
                                 <div className="absolute inset-0">
@@ -480,7 +478,7 @@ export const MainLayout: React.FC = () => {
                                 aria-hidden={!mobileLeftDrawerOpen}
                             >
                                 <ErrorBoundary>
-                                    <SessionSidebar mobileVariant />
+                                    <SessionSidebar mobileVariant isVisible={mobileLeftDrawerVisible} />
                                 </ErrorBoundary>
                             </motion.div>
                             {mobileRightDrawerVisible && (
@@ -520,7 +518,7 @@ export const MainLayout: React.FC = () => {
                             className="border-border/50"
                             topBar={<SidebarTopBar />}
                         >
-                            <SessionSidebar />
+                            <SessionSidebar isVisible={isSidebarOpen} />
                         </Sidebar>
                         <div className="relative flex flex-1 min-w-0 flex-col overflow-hidden bg-background" data-page-scroll-lock="true">
                             <Header />
@@ -530,7 +528,7 @@ export const MainLayout: React.FC = () => {
                                         <div className="relative flex flex-1 min-h-0 min-w-0 overflow-hidden" data-page-scroll-lock="true">
                                             <main className="flex-1 overflow-hidden bg-background relative" data-page-scroll-lock="true">
                                                 <div className={cn('absolute inset-0', !isChatActive && 'invisible')}>
-                                                    <ErrorBoundary><ChatView /></ErrorBoundary>
+                                                    <ErrorBoundary><ChatView active={isChatActive && !isSettingsDialogOpen} /></ErrorBoundary>
                                                 </div>
                                                 {secondaryView && (
                                                     <div className="absolute inset-0">