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/web/server/lib/opencode/settings-runtime.js

@@ -502,14 +502,18 @@ export const createSettingsRuntime = (deps) => {
 
   const writeSettingsToDisk = async (settings) => {
     try {
-      await fsPromises.mkdir(path.dirname(SETTINGS_FILE_PATH), { recursive: true });
+      const settingsDirectory = path.dirname(SETTINGS_FILE_PATH);
+      await fsPromises.mkdir(settingsDirectory, { recursive: true, mode: 0o700 });
+      if (process.platform !== 'win32') await fsPromises.chmod(settingsDirectory, 0o700);
       // Atomic write: Electron main and ssh-manager read this file via plain
       // readFile + JSON.parse and silently coerce parse errors to {}. A
       // partial read during a non-atomic writeFile would make their next
       // read-modify-write wipe the settings file.
       const tmp = `${SETTINGS_FILE_PATH}.tmp-${process.pid}-${Date.now()}-${Math.random().toString(36).slice(2, 8)}`;
-      await fsPromises.writeFile(tmp, JSON.stringify(settings, null, 2), 'utf8');
+      await fsPromises.writeFile(tmp, JSON.stringify(settings, null, 2), { encoding: 'utf8', mode: 0o600 });
+      if (process.platform !== 'win32') await fsPromises.chmod(tmp, 0o600);
       await replaceFile(tmp, SETTINGS_FILE_PATH);
+      if (process.platform !== 'win32') await fsPromises.chmod(SETTINGS_FILE_PATH, 0o600);
     } catch (error) {
       console.warn('Failed to write settings file:', error);
       throw error;