refactor(worker/state): introduce TaskStateService and route mutations through it

Slice 2 of the worker state consolidation refactor (spec sections 2 and 8).

Adds Worker/State/ITaskStateService + TaskStateService as the single component
that mutates Status, PlanningPhase, and BlockedByTaskId. Each transition is one
atomic ExecuteUpdate with a WHERE filter on the expected source status, so
parallel claims are TOCTOU-free. Side effects (queue wake on -> Queued, hub
TaskUpdated broadcast, chain advance + parent completion on terminal child)
are owned by the service so callers no longer need to remember them.

Migrated callers (mechanical, behavior preserved):
- TaskRunner: HandleSuccess/HandleFailure/MarkFailed/RunAsync/ContinueAsync
- StaleTaskRecovery: bulk recover stale Running tasks
- TaskResetService: status flip (worktree cleanup stays in service)
- PlanningSessionManager.StartAsync: status flip via state, token write via repo
- PlanningChainCoordinator.OnChildFinishedAsync: routes the next-sibling write
  through state.UnblockAsync (Slice 4 finishes the rewrite)
- ExternalMcpService.UpdateTaskStatus: Queued case via state.EnqueueAsync

Repo Mark*Async helpers (MarkRunning/MarkDone/MarkFailed/FlipAllRunningToFailed)
are now internal; ClaudeDo.Data grants InternalsVisibleTo to ClaudeDo.Worker
and ClaudeDo.Worker.Tests for the existing repo-level tests.

DI: TaskStateService is registered as Singleton in both the main app and the
external-MCP app; the queue-wake delegate captures sp -> QueueService.WakeQueue
to break the TaskStateService -> QueueService -> TaskRunner -> TaskStateService
construction cycle. PlanningChainCoordinator takes Func<ITaskStateService> for
the same reason; Slice 3 will replace both with IQueueWaker.

Tests: TaskStateServiceTests covers happy + reject for every transition, the
parallel StartRunningAsync claim race, child-terminal chain advancement, and
stale recovery. Existing service/repo tests are updated to construct the new
state-service via a TaskStateServiceBuilder helper. Pre-existing constructor
drift in QueueService/ExternalMcp/PlanningHub tests is patched to keep the
test project building (the surrounding test logic is otherwise untouched).

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

src/ClaudeDo.Worker/Program.cs

@@ -7,6 +7,7 @@ using ClaudeDo.Worker.Hub;
 using ClaudeDo.Worker.Planning;
 using ClaudeDo.Worker.Runner;
 using ClaudeDo.Worker.Services;
+using ClaudeDo.Worker.State;
 using Microsoft.EntityFrameworkCore;
 
 var cfg = WorkerConfig.Load();
@@ -41,6 +42,17 @@ 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.
+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<PlanningChainCoordinator>(),
+    sp.GetRequiredService<ILogger<TaskStateService>>()));
+
 // Agent file management.
 var agentsDir = Path.Combine(ClaudeDo.Data.Paths.AppDataRoot(), "agents");
 Directory.CreateDirectory(agentsDir);
@@ -65,6 +77,7 @@ builder.Services.AddSingleton(sp =>
         sp.GetRequiredService<IDbContextFactory<ClaudeDoDbContext>>(),
         sp.GetRequiredService<GitService>(),
         cfg,
+        sp.GetRequiredService<ITaskStateService>(),
         planningSessionsDir));
 builder.Services.AddSingleton<IPlanningTerminalLauncher>(sp =>
     new WindowsTerminalPlanningLauncher("wt.exe", cfg.ClaudeBin));
@@ -123,6 +136,7 @@ if (cfg.ExternalMcpPort > 0)
     externalBuilder.Services.AddSingleton(app.Services.GetRequiredService<HubBroadcaster>());
     externalBuilder.Services.AddSingleton(app.Services.GetRequiredService<QueueService>());
     externalBuilder.Services.AddSingleton(app.Services.GetRequiredService<IDbContextFactory<ClaudeDoDbContext>>());
+    externalBuilder.Services.AddSingleton(app.Services.GetRequiredService<ITaskStateService>());
     externalBuilder.Services.AddScoped<ClaudeDoDbContext>(sp =>
         sp.GetRequiredService<IDbContextFactory<ClaudeDoDbContext>>().CreateDbContext());
     externalBuilder.Services.AddScoped<TaskRepository>();