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/vscode/src/opencodeAuth.ts

@@ -28,15 +28,18 @@ const readAuthFile = (): AuthFile => {
 const writeAuthFile = (auth: AuthFile): void => {
   try {
     if (!fs.existsSync(OPENCODE_DATA_DIR)) {
-      fs.mkdirSync(OPENCODE_DATA_DIR, { recursive: true });
+      fs.mkdirSync(OPENCODE_DATA_DIR, { recursive: true, mode: 0o700 });
     }
+    if (process.platform !== 'win32') fs.chmodSync(OPENCODE_DATA_DIR, 0o700);
 
     if (fs.existsSync(AUTH_FILE)) {
       const backupFile = `${AUTH_FILE}.openchamber.backup`;
       fs.copyFileSync(AUTH_FILE, backupFile);
+      if (process.platform !== 'win32') fs.chmodSync(backupFile, 0o600);
     }
 
-    fs.writeFileSync(AUTH_FILE, JSON.stringify(auth, null, 2), 'utf8');
+    fs.writeFileSync(AUTH_FILE, JSON.stringify(auth, null, 2), { encoding: 'utf8', mode: 0o600 });
+    if (process.platform !== 'win32') fs.chmodSync(AUTH_FILE, 0o600);
   } catch (error) {
     console.error('Failed to write auth file:', error);
     throw new Error('Failed to write OpenCode auth configuration');