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/session-runtime.test.js

@@ -148,4 +148,84 @@ describe('session runtime', () => {
       vi.useRealTimers();
     }
   });
+
+  it('maintains an idempotent active session count', () => {
+    const runtime = createSessionRuntime({
+      writeSseEvent() {},
+      getNotificationClients: () => new Set(),
+      broadcastEvent() {},
+    });
+    runtimes.push(runtime);
+    const status = (sessionID, type) => runtime.processOpenCodeSsePayload({
+      type: 'session.status',
+      properties: { sessionID, status: { type } },
+    });
+
+    expect(runtime.getActiveSessionCount()).toBe(0);
+    status('session-1', 'busy');
+    status('session-1', 'busy');
+    status('session-1', 'retry');
+    expect(runtime.getActiveSessionCount()).toBe(1);
+
+    status('session-2', 'busy');
+    expect(runtime.getActiveSessionCount()).toBe(2);
+
+    status('session-1', 'idle');
+    expect(runtime.getActiveSessionCount()).toBe(1);
+    status('session-1', 'idle');
+    expect(runtime.getActiveSessionCount()).toBe(1);
+
+    runtime.resetAllSessionActivityToIdle();
+    expect(runtime.getActiveSessionCount()).toBe(0);
+  });
+
+  it('restores activity when busy interrupts cooldown without timer underflow', () => {
+    vi.useFakeTimers();
+    const runtime = createSessionRuntime({
+      writeSseEvent() {},
+      getNotificationClients: () => new Set(),
+      broadcastEvent() {},
+    });
+    const status = (type) => runtime.processOpenCodeSsePayload({
+      type: 'session.status',
+      properties: { sessionID: 'session-1', status: { type } },
+    });
+
+    try {
+      status('busy');
+      status('idle');
+      expect(runtime.getActiveSessionCount()).toBe(0);
+
+      status('retry');
+      expect(runtime.getActiveSessionCount()).toBe(1);
+      vi.advanceTimersByTime(2000);
+
+      expect(runtime.getActiveSessionCount()).toBe(1);
+      expect(runtime.getSessionActivitySnapshot()['session-1']).toEqual({ type: 'busy' });
+    } finally {
+      runtime.dispose();
+      vi.useRealTimers();
+    }
+  });
+
+  it('releases retained session state when disposed', () => {
+    const runtime = createSessionRuntime({
+      writeSseEvent() {},
+      getNotificationClients: () => new Set(),
+      broadcastEvent() {},
+    });
+    runtimes.push(runtime);
+
+    runtime.processOpenCodeSsePayload({
+      type: 'session.status',
+      properties: { sessionID: 'session-1', status: { type: 'busy' } },
+    });
+    runtime.markUserMessageSent('session-1');
+    runtime.dispose();
+
+    expect(runtime.getActiveSessionCount()).toBe(0);
+    expect(runtime.getSessionActivitySnapshot()).toEqual({});
+    expect(runtime.getSessionStateSnapshot()).toEqual({});
+    expect(runtime.getSessionAttentionSnapshot()).toEqual({});
+  });
 });