refactor(worker/queue): split queue waker and picker, auto-wake on enqueue

Slice 3 of the worker state and queue consolidation refactor.

- Add IQueueWaker / QueueWaker (singleton holding the wake semaphore).
- Add IQueuePicker / QueuePicker; raw SQL UPDATE...RETURNING moves out of
  TaskRepository.GetNextQueuedAgentTaskAsync (deleted) and now also filters
  on blocked_by_task_id IS NULL and writes started_at on claim.
- TaskStateService takes IQueueWaker directly; the Func<QueueService>
  indirection is gone. State transitions to Queued auto-wake the dispatcher.
- QueueService waits via the shared waker and dispatches via the picker.
- Drop explicit _queue.WakeQueue() calls in WorkerHub.QueuePlanningSubtasksAsync
  and ExternalMcpService.AddTask. The hub WakeQueue endpoint stays for
  diagnostics, delegating to _waker.Wake().
- Migrate tests; pre-existing flaky AppSettings/ExternalMcp tests untouched.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/ClaudeDo.Worker/Program.cs

@@ -5,6 +5,7 @@ using ClaudeDo.Worker.Config;
 using ClaudeDo.Worker.External;
 using ClaudeDo.Worker.Hub;
 using ClaudeDo.Worker.Planning;
+using ClaudeDo.Worker.Queue;
 using ClaudeDo.Worker.Runner;
 using ClaudeDo.Worker.Services;
 using ClaudeDo.Worker.State;
@@ -42,14 +43,18 @@ builder.Services.AddSingleton<PlanningAggregator>();
 builder.Services.AddSingleton<PlanningMergeOrchestrator>();
 builder.Services.AddSingleton<PlanningChainCoordinator>();
 
-// Centralized status mutation. Use a delegate for WakeQueue to break the
-// TaskStateService → QueueService → TaskRunner → TaskStateService DI cycle;
-// Slice 3 will replace this with IQueueWaker.
+// Queue dispatch primitives. QueueWaker holds the wake semaphore; the queue picker
+// performs atomic Queued→Running claim. Both injected into the state service so it
+// can wake the dispatcher without depending on QueueService directly.
+builder.Services.AddSingleton<QueueWaker>();
+builder.Services.AddSingleton<IQueueWaker>(sp => sp.GetRequiredService<QueueWaker>());
+builder.Services.AddSingleton<IQueuePicker, QueuePicker>();
+
 builder.Services.AddSingleton<Func<ITaskStateService>>(sp => () => sp.GetRequiredService<ITaskStateService>());
 builder.Services.AddSingleton<ITaskStateService>(sp => new TaskStateService(
     sp.GetRequiredService<IDbContextFactory<ClaudeDoDbContext>>(),
     sp.GetRequiredService<HubBroadcaster>(),
-    () => sp.GetRequiredService<QueueService>().WakeQueue(),
+    sp.GetRequiredService<IQueueWaker>(),
     sp.GetRequiredService<PlanningChainCoordinator>(),
     sp.GetRequiredService<ILogger<TaskStateService>>()));
 
@@ -137,6 +142,7 @@ if (cfg.ExternalMcpPort > 0)
     externalBuilder.Services.AddSingleton(app.Services.GetRequiredService<QueueService>());
     externalBuilder.Services.AddSingleton(app.Services.GetRequiredService<IDbContextFactory<ClaudeDoDbContext>>());
     externalBuilder.Services.AddSingleton(app.Services.GetRequiredService<ITaskStateService>());
+    externalBuilder.Services.AddSingleton(app.Services.GetRequiredService<IQueueWaker>());
     externalBuilder.Services.AddScoped<ClaudeDoDbContext>(sp =>
         sp.GetRequiredService<IDbContextFactory<ClaudeDoDbContext>>().CreateDbContext());
     externalBuilder.Services.AddScoped<TaskRepository>();