fix(subagent-watcher): discover workflow-nested agents + harden meta→transcript upgrade

Two follow-ups to db93491 (the 2026-06 CC meta.json format change), after
reverse-engineering the new on-disk layout with a live current-CC subagent +
1Hz fs poller:

(1) Workflow recursion — the Workflow tool nests its agents at
    subagents/workflows/{wf}/agent-{id}.jsonl, one level below the flat
    subagents/ scan, so they were never tracked. Add watchWorkflowDirs()
    (driven from scanForSubagents) to descend and watch each workflow dir
    (idempotent; fs.watch recursive is unsupported on Linux, so the ~5s
    periodic scan re-drives it — same latency as new-session discovery).
    Require the `agent-` prefix in the flat readdir + watch callback so a
    workflow dir's sibling journal.jsonl can't register a bogus "journal" agent.
    E2E verified against real ~/.claude/projects: 32 workflow-nested agents
    discovered (wf_fa35c1d8-4a9), 0 bogus journal agents.

(2) Transcript timing — empirically the per-agent .jsonl IS written at the
    standard subagents/ path and grows incrementally (tailable); the
    /tmp/.../tasks/<id>.output the prior probe found is just a symlink back to
    it. meta.json lands at spawn, the .jsonl a beat later. Add a meta→transcript
    upgrade in registerAgentFile: when an agent registered meta-only gets its
    sibling .jsonl, re-point filePath, drop the stale sidecar context, start
    tailing, and emit subagent:updated (not a duplicate discovered). Corrects the
    now-inaccurate "no transcript to tail" doc comment on registerAgentMeta.

Tests: 2 new cases (workflow-nested discovery; journal.jsonl not registered).
All 56 pass; tsc/lint/format clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

test/subagent-watcher.test.ts

@@ -475,6 +475,65 @@ describe('SubagentWatcher', () => {
     });
   });
 
+  describe('Workflow-nested subagents (subagents/workflows/{wf}/)', () => {
+    // The Workflow tool nests its agents one level deeper than TUI Task subagents:
+    // subagents/workflows/{workflowId}/agent-{id}.jsonl — plus a sibling journal.jsonl.
+    // The flat subagents/ scan misses them; watchWorkflowDirs() descends one level.
+    function mockWorkflowLayout(wfFiles: string[]) {
+      mockReaddirSync.mockImplementation((path: string) => {
+        const p = String(path);
+        if (p.endsWith('wf_test')) return wfFiles;
+        if (p.endsWith('workflows')) return ['wf_test'];
+        if (p.endsWith('subagents')) return ['workflows']; // no flat agents, just the workflows dir
+        if (p.includes('session1')) return ['subagents'];
+        if (p.includes('project1')) return ['session1'];
+        return ['project1'];
+      });
+      mockStatSync.mockReturnValue({
+        isDirectory: () => true,
+        birthtime: new Date(),
+        mtime: new Date(),
+        size: 100,
+      });
+      const mockRl = createMockRl();
+      mockCreateInterface.mockReturnValue(mockRl);
+      return mockRl;
+    }
+
+    it('should discover an agent nested under subagents/workflows/{wf}/', async () => {
+      mockExistsSync.mockReturnValue(true); // sibling .jsonl exists for the meta
+      const mockRl = mockWorkflowLayout(['agent-wf1.jsonl', 'agent-wf1.meta.json', 'journal.jsonl']);
+
+      const discoveredHandler = vi.fn();
+      watcher.on('subagent:discovered', discoveredHandler);
+
+      watcher.start();
+      await flushAsyncScan();
+      mockRl.emit('close');
+      await vi.advanceTimersByTimeAsync(100);
+
+      expect(discoveredHandler).toHaveBeenCalled();
+      const info = discoveredHandler.mock.calls[0][0] as SubagentInfo;
+      expect(info.agentId).toBe('wf1');
+      expect(info.filePath.endsWith('.jsonl')).toBe(true);
+      expect(info.filePath).toContain('workflows');
+    });
+
+    it('should NOT register a workflow dir journal.jsonl as a bogus agent', async () => {
+      mockExistsSync.mockReturnValue(true);
+      const mockRl = mockWorkflowLayout(['agent-wf1.jsonl', 'journal.jsonl']);
+
+      watcher.start();
+      await flushAsyncScan();
+      mockRl.emit('close');
+      await vi.advanceTimersByTimeAsync(100);
+
+      const agents = watcher.getSubagents();
+      expect(agents).toHaveLength(1); // only agent-wf1, never "journal"
+      expect(agents.every((a) => a.agentId !== 'journal')).toBe(true);
+    });
+  });
+
   describe('Status Lifecycle', () => {
     it('should start agents as active', async () => {
       const mockRl = createMockRl();