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/VSCodeLayout.tsx

@@ -251,6 +251,10 @@ export const VSCodeLayout: React.FC = () => {
     setCurrentView('sessions');
   }, []);
 
+  const handleSessionSelected = React.useCallback(() => {
+    setCurrentView('chat');
+  }, []);
+
   const isSessionInActiveWorkspace = React.useCallback((session: Session): boolean => {
     if (!activeWorkspacePath) {
       return false;
@@ -590,7 +594,7 @@ export const VSCodeLayout: React.FC = () => {
             />
             <div className="flex-1 overflow-hidden">
               <ErrorBoundary>
-                <ChatView />
+                <ChatView active={currentView === 'chat'} />
               </ErrorBoundary>
             </div>
           </div>
@@ -609,7 +613,7 @@ export const VSCodeLayout: React.FC = () => {
                 <SessionSidebar
                   mobileVariant
                   allowReselect
-                  onSessionSelected={() => setCurrentView('chat')}
+                  onSessionSelected={handleSessionSelected}
                   hideDirectoryControls
                 />
               </div>
@@ -628,7 +632,7 @@ export const VSCodeLayout: React.FC = () => {
             />
             <div className="flex-1 overflow-hidden">
               <ErrorBoundary>
-                <ChatView />
+                <ChatView active={currentView === 'chat'} />
               </ErrorBoundary>
             </div>
           </div>