diff --git a/src/ClaudeDo.Data/ClaudeDo.Data.csproj b/src/ClaudeDo.Data/ClaudeDo.Data.csproj
index ec9a23e..81866bf 100644
--- a/src/ClaudeDo.Data/ClaudeDo.Data.csproj
+++ b/src/ClaudeDo.Data/ClaudeDo.Data.csproj
@@ -14,4 +14,9 @@
     </PackageReference>
   </ItemGroup>
 
+  <ItemGroup>
+    <InternalsVisibleTo Include="ClaudeDo.Worker" />
+    <InternalsVisibleTo Include="ClaudeDo.Worker.Tests" />
+  </ItemGroup>
+
 </Project>
diff --git a/src/ClaudeDo.Data/Repositories/TaskRepository.cs b/src/ClaudeDo.Data/Repositories/TaskRepository.cs
index 48ca97a..5c76d14 100644
--- a/src/ClaudeDo.Data/Repositories/TaskRepository.cs
+++ b/src/ClaudeDo.Data/Repositories/TaskRepository.cs
@@ -88,7 +88,7 @@ public sealed class TaskRepository
 
     #region Status transitions
 
-    public async Task MarkRunningAsync(string taskId, DateTime startedAt, CancellationToken ct = default)
+    internal async Task MarkRunningAsync(string taskId, DateTime startedAt, CancellationToken ct = default)
     {
         await _context.Tasks
             .Where(t => t.Id == taskId)
@@ -97,7 +97,7 @@ public sealed class TaskRepository
                 .SetProperty(t => t.StartedAt, startedAt), ct);
     }
 
-    public async Task MarkDoneAsync(string taskId, DateTime finishedAt, string? result, CancellationToken ct = default)
+    internal async Task MarkDoneAsync(string taskId, DateTime finishedAt, string? result, CancellationToken ct = default)
     {
         await _context.Tasks
             .Where(t => t.Id == taskId)
@@ -107,7 +107,7 @@ public sealed class TaskRepository
                 .SetProperty(t => t.Result, result), ct);
     }
 
-    public async Task MarkFailedAsync(string taskId, DateTime finishedAt, string? result, CancellationToken ct = default)
+    internal async Task MarkFailedAsync(string taskId, DateTime finishedAt, string? result, CancellationToken ct = default)
     {
         await _context.Tasks
             .Where(t => t.Id == taskId)
@@ -124,7 +124,7 @@ public sealed class TaskRepository
             .ExecuteUpdateAsync(s => s.SetProperty(t => t.LogPath, logPath), ct);
     }
 
-    public async Task<int> FlipAllRunningToFailedAsync(string reason, CancellationToken ct = default)
+    internal async Task<int> FlipAllRunningToFailedAsync(string reason, CancellationToken ct = default)
     {
         var resultText = "[stale] " + reason;
         var now = DateTime.UtcNow;
@@ -364,6 +364,17 @@ public sealed class TaskRepository
         return await _context.Tasks.AsNoTracking().FirstOrDefaultAsync(t => t.Id == taskId, ct);
     }
 
+    public async Task SetPlanningSessionTokenAsync(
+        string taskId,
+        string sessionToken,
+        CancellationToken ct = default)
+    {
+        await _context.Tasks
+            .Where(t => t.Id == taskId)
+            .ExecuteUpdateAsync(s => s
+                .SetProperty(t => t.PlanningSessionToken, sessionToken), ct);
+    }
+
     public async Task UpdatePlanningSessionIdAsync(
         string parentId,
         string sessionId,
diff --git a/src/ClaudeDo.Worker/External/ExternalMcpService.cs b/src/ClaudeDo.Worker/External/ExternalMcpService.cs
index 3db5ef5..4573cbe 100644
--- a/src/ClaudeDo.Worker/External/ExternalMcpService.cs
+++ b/src/ClaudeDo.Worker/External/ExternalMcpService.cs
@@ -3,6 +3,7 @@ using ClaudeDo.Data.Models;
 using ClaudeDo.Data.Repositories;
 using ClaudeDo.Worker.Hub;
 using ClaudeDo.Worker.Services;
+using ClaudeDo.Worker.State;
 using ModelContextProtocol.Server;
 using TaskStatus = ClaudeDo.Data.Models.TaskStatus;
 
@@ -32,19 +33,22 @@ public sealed class ExternalMcpService
     private readonly QueueService _queue;
     private readonly HubBroadcaster _broadcaster;
     private readonly TagRepository _tags;
+    private readonly ITaskStateService _state;
 
     public ExternalMcpService(
         TaskRepository tasks,
         ListRepository lists,
         QueueService queue,
         HubBroadcaster broadcaster,
-        TagRepository tags)
+        TagRepository tags,
+        ITaskStateService state)
     {
         _tasks = tasks;
         _lists = lists;
         _queue = queue;
         _broadcaster = broadcaster;
         _tags = tags;
+        _state = state;
     }
 
     [McpServerTool, Description("List all task lists available in ClaudeDo.")]
@@ -173,14 +177,13 @@ public sealed class ExternalMcpService
         {
             case TaskStatus.Manual:
                 await _tasks.ResetToManualAsync(taskId, cancellationToken);
+                await _broadcaster.TaskUpdated(taskId);
                 break;
 
             case TaskStatus.Queued:
-                if (task.Status is TaskStatus.Running)
-                    throw new InvalidOperationException("Cannot enqueue a running task.");
-                task.Status = TaskStatus.Queued;
-                await _tasks.UpdateAsync(task, cancellationToken);
-                _queue.WakeQueue();
+                var enqueueResult = await _state.EnqueueAsync(taskId, cancellationToken);
+                if (!enqueueResult.Ok)
+                    throw new InvalidOperationException(enqueueResult.Reason ?? "Cannot enqueue task.");
                 break;
 
             default:
@@ -189,7 +192,6 @@ public sealed class ExternalMcpService
         }
 
         var reload = (await _tasks.GetByIdAsync(taskId, cancellationToken))!;
-        await _broadcaster.TaskUpdated(taskId);
         return ToDto(reload);
     }
 
diff --git a/src/ClaudeDo.Worker/Planning/PlanningChainCoordinator.cs b/src/ClaudeDo.Worker/Planning/PlanningChainCoordinator.cs
index ce608ea..873d93c 100644
--- a/src/ClaudeDo.Worker/Planning/PlanningChainCoordinator.cs
+++ b/src/ClaudeDo.Worker/Planning/PlanningChainCoordinator.cs
@@ -1,5 +1,6 @@
 using ClaudeDo.Data;
 using ClaudeDo.Data.Models;
+using ClaudeDo.Worker.State;
 using Microsoft.EntityFrameworkCore;
 using TaskStatus = ClaudeDo.Data.Models.TaskStatus;
 
@@ -8,9 +9,15 @@ namespace ClaudeDo.Worker.Planning;
 public sealed class PlanningChainCoordinator
 {
     private readonly IDbContextFactory<ClaudeDoDbContext> _dbFactory;
+    private readonly Func<ITaskStateService> _state;
 
-    public PlanningChainCoordinator(IDbContextFactory<ClaudeDoDbContext> dbFactory)
-        => _dbFactory = dbFactory;
+    public PlanningChainCoordinator(
+        IDbContextFactory<ClaudeDoDbContext> dbFactory,
+        Func<ITaskStateService> state)
+    {
+        _dbFactory = dbFactory;
+        _state = state;
+    }
 
     public async Task QueueSubtasksSequentiallyAsync(string parentTaskId, CancellationToken ct = default)
     {
@@ -56,6 +63,7 @@ public sealed class PlanningChainCoordinator
         if (child?.ParentTaskId is null) return null;
 
         var next = await ctx.Tasks
+            .AsNoTracking()
             .Where(t => t.ParentTaskId == child.ParentTaskId
                      && t.SortOrder > child.SortOrder
                      && t.Status == TaskStatus.Waiting)
@@ -63,8 +71,7 @@ public sealed class PlanningChainCoordinator
             .FirstOrDefaultAsync(ct);
         if (next is null) return null;
 
-        next.Status = TaskStatus.Queued;
-        await ctx.SaveChangesAsync(ct);
+        await _state().UnblockAsync(next.Id, ct);
         return next.Id;
     }
 }
diff --git a/src/ClaudeDo.Worker/Planning/PlanningSessionManager.cs b/src/ClaudeDo.Worker/Planning/PlanningSessionManager.cs
index 2d82d8d..875dcb4 100644
--- a/src/ClaudeDo.Worker/Planning/PlanningSessionManager.cs
+++ b/src/ClaudeDo.Worker/Planning/PlanningSessionManager.cs
@@ -6,6 +6,7 @@ using ClaudeDo.Data.Git;
 using ClaudeDo.Data.Models;
 using ClaudeDo.Data.Repositories;
 using ClaudeDo.Worker.Config;
+using ClaudeDo.Worker.State;
 using Microsoft.EntityFrameworkCore;
 using TaskStatus = ClaudeDo.Data.Models.TaskStatus;
 
@@ -22,17 +23,20 @@ public sealed class PlanningSessionManager
     private readonly GitService _git;
     private readonly WorkerConfig _cfg;
     private readonly string _rootDirectory;
+    private readonly ITaskStateService? _state;
 
     // DI constructor.
     public PlanningSessionManager(
         IDbContextFactory<ClaudeDoDbContext> factory,
         GitService git,
         WorkerConfig cfg,
+        ITaskStateService state,
         string rootDirectory)
     {
         _factory = factory;
         _git = git;
         _cfg = cfg;
+        _state = state;
         _rootDirectory = rootDirectory;
     }
 
@@ -43,13 +47,15 @@ public sealed class PlanningSessionManager
         AppSettingsRepository settings,
         GitService git,
         WorkerConfig cfg,
-        string rootDirectory)
+        string rootDirectory,
+        ITaskStateService? state = null)
     {
         _tasksOverride = tasks;
         _listsOverride = lists;
         _settingsOverride = settings;
         _git = git;
         _cfg = cfg;
+        _state = state;
         _rootDirectory = rootDirectory;
     }
 
@@ -114,8 +120,19 @@ public sealed class PlanningSessionManager
 
         // Session dir + token + prompt files.
         var token = GenerateToken();
-        var started = await tasks.SetPlanningStartedAsync(taskId, token, ct)
-            ?? throw new InvalidOperationException("Failed to transition task to Planning.");
+        if (_state is not null)
+        {
+            var startResult = await _state.StartPlanningAsync(taskId, ct);
+            if (!startResult.Ok)
+                throw new InvalidOperationException(startResult.Reason ?? "Failed to transition task to Planning.");
+            await tasks.SetPlanningSessionTokenAsync(taskId, token, ct);
+        }
+        else
+        {
+            // Test fallback when no state-service is provided.
+            if (await tasks.SetPlanningStartedAsync(taskId, token, ct) is null)
+                throw new InvalidOperationException("Failed to transition task to Planning.");
+        }
 
         var sessionDir = Path.Combine(_rootDirectory, taskId);
         Directory.CreateDirectory(sessionDir);
diff --git a/src/ClaudeDo.Worker/Program.cs b/src/ClaudeDo.Worker/Program.cs
index 2e19c36..bbd9044 100644
--- a/src/ClaudeDo.Worker/Program.cs
+++ b/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>();
diff --git a/src/ClaudeDo.Worker/Runner/TaskRunner.cs b/src/ClaudeDo.Worker/Runner/TaskRunner.cs
index aae0ea0..cdada3d 100644
--- a/src/ClaudeDo.Worker/Runner/TaskRunner.cs
+++ b/src/ClaudeDo.Worker/Runner/TaskRunner.cs
@@ -3,7 +3,7 @@ using ClaudeDo.Data.Models;
 using ClaudeDo.Data.Repositories;
 using ClaudeDo.Worker.Config;
 using ClaudeDo.Worker.Hub;
-using ClaudeDo.Worker.Planning;
+using ClaudeDo.Worker.State;
 using Microsoft.EntityFrameworkCore;
 using TaskStatus = ClaudeDo.Data.Models.TaskStatus;
 
@@ -18,7 +18,7 @@ public sealed class TaskRunner
     private readonly ClaudeArgsBuilder _argsBuilder;
     private readonly WorkerConfig _cfg;
     private readonly ILogger<TaskRunner> _logger;
-    private readonly PlanningChainCoordinator _chain;
+    private readonly ITaskStateService _state;
 
     public TaskRunner(
         IClaudeProcess claude,
@@ -28,7 +28,7 @@ public sealed class TaskRunner
         ClaudeArgsBuilder argsBuilder,
         WorkerConfig cfg,
         ILogger<TaskRunner> logger,
-        PlanningChainCoordinator chain)
+        ITaskStateService state)
     {
         _claude = claude;
         _dbFactory = dbFactory;
@@ -37,7 +37,7 @@ public sealed class TaskRunner
         _argsBuilder = argsBuilder;
         _cfg = cfg;
         _logger = logger;
-        _chain = chain;
+        _state = state;
     }
 
     public async Task RunAsync(TaskEntity task, string slot, CancellationToken ct)
@@ -91,11 +91,7 @@ public sealed class TaskRunner
             var resolvedConfig = await ResolveConfigAsync(task, listConfig, null, ct);
 
             var now = DateTime.UtcNow;
-            using (var context = _dbFactory.CreateDbContext())
-            {
-                var taskRepo = new TaskRepository(context);
-                await taskRepo.MarkRunningAsync(task.Id, now, ct);
-            }
+            await _state.StartRunningAsync(task.Id, now, ct);
             await _broadcaster.TaskStarted(slot, task.Id, now);
 
             // Build prompt.
@@ -202,11 +198,7 @@ public sealed class TaskRunner
         }
 
         var now = DateTime.UtcNow;
-        using (var context = _dbFactory.CreateDbContext())
-        {
-            var taskRepo = new TaskRepository(context);
-            await taskRepo.MarkRunningAsync(taskId, now, ct);
-        }
+        await _state.StartRunningAsync(taskId, now, ct);
         await _broadcaster.TaskStarted(slot, taskId, now);
 
         var nextRunNumber = lastRun.RunNumber + 1;
@@ -332,34 +324,11 @@ public sealed class TaskRunner
         // is never left as 'running' because of a cancel that arrived
         // after the Claude run already succeeded.
         var finishedAt = DateTime.UtcNow;
-        using (var context = _dbFactory.CreateDbContext())
-        {
-            var taskRepo = new TaskRepository(context);
-            await taskRepo.MarkDoneAsync(task.Id, finishedAt, result.ResultMarkdown, CancellationToken.None);
-            if (task.ParentTaskId is not null)
-                await taskRepo.TryCompleteParentAsync(task.ParentTaskId, CancellationToken.None);
-        }
+        await _state.CompleteAsync(task.Id, finishedAt, result.ResultMarkdown, CancellationToken.None);
         await _broadcaster.WorkerLog($"Finished \"{task.Title}\" (done)", WorkerLogLevel.Success, DateTime.UtcNow);
         await _broadcaster.TaskFinished(slot, task.Id, "done", finishedAt);
         _logger.LogInformation("Task {TaskId} completed (turns={Turns}, tokens_in={In}, tokens_out={Out})",
             task.Id, result.TurnCount, result.TokensIn, result.TokensOut);
-
-        // Sequential planning chain: if this task has a parent, flip the next
-        // Waiting sibling to Queued so the queue pickup loop dispatches it next.
-        if (task.ParentTaskId is not null)
-        {
-            try
-            {
-                var advanced = await _chain.OnChildFinishedAsync(
-                    task.Id, TaskStatus.Done, CancellationToken.None);
-                if (advanced is not null)
-                    await _broadcaster.TaskUpdated(advanced);
-            }
-            catch (Exception ex)
-            {
-                _logger.LogWarning(ex, "PlanningChain advance failed for {TaskId}", task.Id);
-            }
-        }
     }
 
     private async Task HandleFailure(string taskId, string taskTitle, string slot, RunResult result)
@@ -367,12 +336,7 @@ public sealed class TaskRunner
         // Intentionally does not accept a CancellationToken: this is the
         // terminal write for a failed task and must always be persisted.
         var finishedAt = DateTime.UtcNow;
-        using var context = _dbFactory.CreateDbContext();
-        var taskRepo = new TaskRepository(context);
-        await taskRepo.MarkFailedAsync(taskId, finishedAt, result.ErrorMarkdown, CancellationToken.None);
-        var justFailed = await taskRepo.GetByIdAsync(taskId, CancellationToken.None);
-        if (justFailed?.ParentTaskId is not null)
-            await taskRepo.TryCompleteParentAsync(justFailed.ParentTaskId, CancellationToken.None);
+        await _state.FailAsync(taskId, finishedAt, result.ErrorMarkdown, CancellationToken.None);
         await _broadcaster.WorkerLog($"Finished \"{taskTitle}\" (failed)", WorkerLogLevel.Error, DateTime.UtcNow);
         await _broadcaster.TaskFinished(slot, taskId, "failed", finishedAt);
         _logger.LogWarning("Task {TaskId} failed (turns={Turns}): {Error}", taskId, result.TurnCount, result.ErrorMarkdown);
@@ -384,15 +348,9 @@ public sealed class TaskRunner
         {
             var now = DateTime.UtcNow;
             // Terminal write — never cancel.
-            using var context = _dbFactory.CreateDbContext();
-            var taskRepo = new TaskRepository(context);
-            await taskRepo.MarkFailedAsync(taskId, now, error, CancellationToken.None);
-            var justFailed = await taskRepo.GetByIdAsync(taskId, CancellationToken.None);
-            if (justFailed?.ParentTaskId is not null)
-                await taskRepo.TryCompleteParentAsync(justFailed.ParentTaskId, CancellationToken.None);
+            await _state.FailAsync(taskId, now, error, CancellationToken.None);
             await _broadcaster.WorkerLog($"Finished \"{taskTitle}\" (failed)", WorkerLogLevel.Error, DateTime.UtcNow);
             await _broadcaster.TaskFinished(slot, taskId, "failed", now);
-            await _broadcaster.TaskUpdated(taskId);
         }
         catch (Exception ex)
         {
diff --git a/src/ClaudeDo.Worker/Services/StaleTaskRecovery.cs b/src/ClaudeDo.Worker/Services/StaleTaskRecovery.cs
index 7ad3df7..c45ab4f 100644
--- a/src/ClaudeDo.Worker/Services/StaleTaskRecovery.cs
+++ b/src/ClaudeDo.Worker/Services/StaleTaskRecovery.cs
@@ -1,25 +1,21 @@
-using ClaudeDo.Data;
-using ClaudeDo.Data.Repositories;
-using Microsoft.EntityFrameworkCore;
+using ClaudeDo.Worker.State;
 
 namespace ClaudeDo.Worker.Services;
 
 public sealed class StaleTaskRecovery : IHostedService
 {
-    private readonly IDbContextFactory<ClaudeDoDbContext> _dbFactory;
+    private readonly ITaskStateService _state;
     private readonly ILogger<StaleTaskRecovery> _logger;
 
-    public StaleTaskRecovery(IDbContextFactory<ClaudeDoDbContext> dbFactory, ILogger<StaleTaskRecovery> logger)
+    public StaleTaskRecovery(ITaskStateService state, ILogger<StaleTaskRecovery> logger)
     {
-        _dbFactory = dbFactory;
+        _state = state;
         _logger = logger;
     }
 
     public async Task StartAsync(CancellationToken cancellationToken)
     {
-        using var context = _dbFactory.CreateDbContext();
-        var tasks = new TaskRepository(context);
-        var flipped = await tasks.FlipAllRunningToFailedAsync("worker restart", cancellationToken);
+        var flipped = await _state.RecoverStaleRunningAsync("worker restart", cancellationToken);
         if (flipped > 0)
             _logger.LogWarning("Stale task recovery: flipped {Count} running task(s) to failed", flipped);
         else
diff --git a/src/ClaudeDo.Worker/Services/TaskResetService.cs b/src/ClaudeDo.Worker/Services/TaskResetService.cs
index f8b3372..314dff5 100644
--- a/src/ClaudeDo.Worker/Services/TaskResetService.cs
+++ b/src/ClaudeDo.Worker/Services/TaskResetService.cs
@@ -3,6 +3,7 @@ using ClaudeDo.Data.Models;
 using ClaudeDo.Data.Repositories;
 using ClaudeDo.Worker.Hub;
 using ClaudeDo.Worker.Runner;
+using ClaudeDo.Worker.State;
 using Microsoft.EntityFrameworkCore;
 using TaskStatus = ClaudeDo.Data.Models.TaskStatus;
 
@@ -13,17 +14,20 @@ public sealed class TaskResetService
     private readonly IDbContextFactory<ClaudeDoDbContext> _dbFactory;
     private readonly WorktreeManager _wtManager;
     private readonly HubBroadcaster _broadcaster;
+    private readonly ITaskStateService _state;
     private readonly ILogger<TaskResetService> _logger;
 
     public TaskResetService(
         IDbContextFactory<ClaudeDoDbContext> dbFactory,
         WorktreeManager wtManager,
         HubBroadcaster broadcaster,
+        ITaskStateService state,
         ILogger<TaskResetService> logger)
     {
         _dbFactory = dbFactory;
         _wtManager = wtManager;
         _broadcaster = broadcaster;
+        _state = state;
         _logger = logger;
     }
 
@@ -55,16 +59,13 @@ public sealed class TaskResetService
             worktreeChanged = true;
         }
 
-        using (var ctx = _dbFactory.CreateDbContext())
-        {
-            await new TaskRepository(ctx).ResetToManualAsync(taskId, ct);
-        }
+        await _state.ResetToIdleAsync(taskId, ct);
 
         await _broadcaster.TaskUpdated(taskId);
         if (worktreeChanged)
             await _broadcaster.WorktreeUpdated(taskId);
 
-        _logger.LogInformation("Reset task {TaskId} to Manual (worktree discarded: {Discarded})", taskId, worktreeChanged);
+        _logger.LogInformation("Reset task {TaskId} to Idle (worktree discarded: {Discarded})", taskId, worktreeChanged);
         await _broadcaster.WorkerLog($"Reset \"{task.Title}\"", WorkerLogLevel.Warn, DateTime.UtcNow);
     }
 }
diff --git a/src/ClaudeDo.Worker/State/ITaskStateService.cs b/src/ClaudeDo.Worker/State/ITaskStateService.cs
new file mode 100644
index 0000000..9d22df9
--- /dev/null
+++ b/src/ClaudeDo.Worker/State/ITaskStateService.cs
@@ -0,0 +1,19 @@
+namespace ClaudeDo.Worker.State;
+
+public interface ITaskStateService
+{
+    Task<TransitionResult> EnqueueAsync(string taskId, CancellationToken ct);
+    Task<TransitionResult> StartRunningAsync(string taskId, DateTime startedAt, CancellationToken ct);
+    Task<TransitionResult> CompleteAsync(string taskId, DateTime finishedAt, string? result, CancellationToken ct);
+    Task<TransitionResult> FailAsync(string taskId, DateTime finishedAt, string? error, CancellationToken ct);
+    Task<TransitionResult> CancelAsync(string taskId, DateTime finishedAt, CancellationToken ct);
+    Task<TransitionResult> ResetToIdleAsync(string taskId, CancellationToken ct);
+
+    Task<TransitionResult> StartPlanningAsync(string parentId, CancellationToken ct);
+    Task<TransitionResult> FinalizePlanningAsync(string parentId, CancellationToken ct);
+
+    Task<TransitionResult> BlockOnAsync(string taskId, string predecessorTaskId, CancellationToken ct);
+    Task<TransitionResult> UnblockAsync(string taskId, CancellationToken ct);
+
+    Task<int> RecoverStaleRunningAsync(string reason, CancellationToken ct);
+}
diff --git a/src/ClaudeDo.Worker/State/TaskStateService.cs b/src/ClaudeDo.Worker/State/TaskStateService.cs
new file mode 100644
index 0000000..dc976b0
--- /dev/null
+++ b/src/ClaudeDo.Worker/State/TaskStateService.cs
@@ -0,0 +1,258 @@
+using ClaudeDo.Data;
+using ClaudeDo.Data.Models;
+using ClaudeDo.Data.Repositories;
+using ClaudeDo.Worker.Hub;
+using ClaudeDo.Worker.Planning;
+using Microsoft.EntityFrameworkCore;
+using TaskStatus = ClaudeDo.Data.Models.TaskStatus;
+
+namespace ClaudeDo.Worker.State;
+
+public sealed class TaskStateService : ITaskStateService
+{
+    private readonly IDbContextFactory<ClaudeDoDbContext> _dbFactory;
+    private readonly HubBroadcaster _broadcaster;
+    private readonly Action _wakeQueue;
+    private readonly PlanningChainCoordinator _chain;
+    private readonly ILogger<TaskStateService> _logger;
+
+    public TaskStateService(
+        IDbContextFactory<ClaudeDoDbContext> dbFactory,
+        HubBroadcaster broadcaster,
+        Action wakeQueue,
+        PlanningChainCoordinator chain,
+        ILogger<TaskStateService> logger)
+    {
+        _dbFactory = dbFactory;
+        _broadcaster = broadcaster;
+        _wakeQueue = wakeQueue;
+        _chain = chain;
+        _logger = logger;
+    }
+
+    public async Task<TransitionResult> EnqueueAsync(string taskId, CancellationToken ct)
+    {
+        await using var ctx = await _dbFactory.CreateDbContextAsync(ct);
+        var affected = await ctx.Tasks
+            .Where(t => t.Id == taskId && t.Status != TaskStatus.Running)
+            .ExecuteUpdateAsync(s => s.SetProperty(t => t.Status, TaskStatus.Queued), ct);
+
+        if (affected == 0)
+            return new TransitionResult(false, "Task not found or already running.");
+
+        _wakeQueue();
+        await _broadcaster.TaskUpdated(taskId);
+        return new TransitionResult(true, null);
+    }
+
+    public async Task<TransitionResult> StartRunningAsync(string taskId, DateTime startedAt, CancellationToken ct)
+    {
+        await using var ctx = await _dbFactory.CreateDbContextAsync(ct);
+        var affected = await ctx.Tasks
+            .Where(t => t.Id == taskId && t.Status != TaskStatus.Running)
+            .ExecuteUpdateAsync(s => s
+                .SetProperty(t => t.Status, TaskStatus.Running)
+                .SetProperty(t => t.StartedAt, startedAt), ct);
+
+        if (affected == 0)
+            return new TransitionResult(false, "Task already running or not found.");
+
+        await _broadcaster.TaskUpdated(taskId);
+        return new TransitionResult(true, null);
+    }
+
+    public async Task<TransitionResult> CompleteAsync(string taskId, DateTime finishedAt, string? result, CancellationToken ct)
+    {
+        await using (var ctx = await _dbFactory.CreateDbContextAsync(ct))
+        {
+            var affected = await ctx.Tasks
+                .Where(t => t.Id == taskId && t.Status == TaskStatus.Running)
+                .ExecuteUpdateAsync(s => s
+                    .SetProperty(t => t.Status, TaskStatus.Done)
+                    .SetProperty(t => t.FinishedAt, finishedAt)
+                    .SetProperty(t => t.Result, result), ct);
+
+            if (affected == 0)
+                return new TransitionResult(false, "Task not running; cannot complete.");
+        }
+
+        await OnChildTerminalAsync(taskId, TaskStatus.Done);
+        await _broadcaster.TaskUpdated(taskId);
+        return new TransitionResult(true, null);
+    }
+
+    public async Task<TransitionResult> FailAsync(string taskId, DateTime finishedAt, string? error, CancellationToken ct)
+    {
+        await using (var ctx = await _dbFactory.CreateDbContextAsync(ct))
+        {
+            var affected = await ctx.Tasks
+                .Where(t => t.Id == taskId && t.Status != TaskStatus.Done)
+                .ExecuteUpdateAsync(s => s
+                    .SetProperty(t => t.Status, TaskStatus.Failed)
+                    .SetProperty(t => t.FinishedAt, finishedAt)
+                    .SetProperty(t => t.Result, error), ct);
+
+            if (affected == 0)
+                return new TransitionResult(false, "Task already done; cannot fail.");
+        }
+
+        await OnChildTerminalAsync(taskId, TaskStatus.Failed);
+        await _broadcaster.TaskUpdated(taskId);
+        return new TransitionResult(true, null);
+    }
+
+    public async Task<TransitionResult> CancelAsync(string taskId, DateTime finishedAt, CancellationToken ct)
+    {
+        await using (var ctx = await _dbFactory.CreateDbContextAsync(ct))
+        {
+            var affected = await ctx.Tasks
+                .Where(t => t.Id == taskId &&
+                    (t.Status == TaskStatus.Running || t.Status == TaskStatus.Queued))
+                .ExecuteUpdateAsync(s => s
+                    .SetProperty(t => t.Status, TaskStatus.Cancelled)
+                    .SetProperty(t => t.FinishedAt, finishedAt), ct);
+
+            if (affected == 0)
+                return new TransitionResult(false, "Task not in cancellable state.");
+        }
+
+        await OnChildTerminalAsync(taskId, TaskStatus.Cancelled);
+        await _broadcaster.TaskUpdated(taskId);
+        return new TransitionResult(true, null);
+    }
+
+    public async Task<TransitionResult> ResetToIdleAsync(string taskId, CancellationToken ct)
+    {
+        await using var ctx = await _dbFactory.CreateDbContextAsync(ct);
+        var affected = await ctx.Tasks
+            .Where(t => t.Id == taskId && t.Status != TaskStatus.Running)
+            .ExecuteUpdateAsync(s => s
+                .SetProperty(t => t.Status, TaskStatus.Idle)
+                .SetProperty(t => t.StartedAt, (DateTime?)null)
+                .SetProperty(t => t.FinishedAt, (DateTime?)null)
+                .SetProperty(t => t.Result, (string?)null), ct);
+
+        if (affected == 0)
+            return new TransitionResult(false, "Task is running; cannot reset.");
+
+        await _broadcaster.TaskUpdated(taskId);
+        return new TransitionResult(true, null);
+    }
+
+    public async Task<TransitionResult> StartPlanningAsync(string parentId, CancellationToken ct)
+    {
+        await using var ctx = await _dbFactory.CreateDbContextAsync(ct);
+        var affected = await ctx.Tasks
+            .Where(t => t.Id == parentId &&
+                (t.Status == TaskStatus.Manual || t.Status == TaskStatus.Idle))
+            .ExecuteUpdateAsync(s => s
+                .SetProperty(t => t.Status, TaskStatus.Planning)
+                .SetProperty(t => t.PlanningPhase, PlanningPhase.Active), ct);
+
+        if (affected == 0)
+            return new TransitionResult(false, "Task not in plannable state.");
+
+        await _broadcaster.TaskUpdated(parentId);
+        return new TransitionResult(true, null);
+    }
+
+    public async Task<TransitionResult> FinalizePlanningAsync(string parentId, CancellationToken ct)
+    {
+        await using var ctx = await _dbFactory.CreateDbContextAsync(ct);
+        var affected = await ctx.Tasks
+            .Where(t => t.Id == parentId && t.PlanningPhase == PlanningPhase.Active)
+            .ExecuteUpdateAsync(s => s
+                .SetProperty(t => t.PlanningPhase, PlanningPhase.Finalized)
+                .SetProperty(t => t.PlanningFinalizedAt, DateTime.UtcNow), ct);
+
+        if (affected == 0)
+            return new TransitionResult(false, "No active planning session.");
+
+        await _broadcaster.TaskUpdated(parentId);
+        return new TransitionResult(true, null);
+    }
+
+    public async Task<TransitionResult> BlockOnAsync(string taskId, string predecessorTaskId, CancellationToken ct)
+    {
+        await using var ctx = await _dbFactory.CreateDbContextAsync(ct);
+        var affected = await ctx.Tasks
+            .Where(t => t.Id == taskId)
+            .ExecuteUpdateAsync(s => s.SetProperty(t => t.BlockedByTaskId, predecessorTaskId), ct);
+
+        if (affected == 0)
+            return new TransitionResult(false, "Task not found.");
+
+        await _broadcaster.TaskUpdated(taskId);
+        return new TransitionResult(true, null);
+    }
+
+    public async Task<TransitionResult> UnblockAsync(string taskId, CancellationToken ct)
+    {
+        await using var ctx = await _dbFactory.CreateDbContextAsync(ct);
+        var affected = await ctx.Tasks
+            .Where(t => t.Id == taskId)
+            .ExecuteUpdateAsync(s => s.SetProperty(t => t.BlockedByTaskId, (string?)null), ct);
+
+        if (affected == 0)
+            return new TransitionResult(false, "Task not found.");
+
+        // Bridge to legacy chain layout: a Waiting predecessor-blocked sibling becomes Queued
+        // when its predecessor finishes. New layout (post-Slice 4) stores siblings as
+        // Status=Queued + BlockedByTaskId set, so this is a no-op for them.
+        await ctx.Tasks
+            .Where(t => t.Id == taskId && t.Status == TaskStatus.Waiting)
+            .ExecuteUpdateAsync(s => s.SetProperty(t => t.Status, TaskStatus.Queued), ct);
+
+        _wakeQueue();
+        await _broadcaster.TaskUpdated(taskId);
+        return new TransitionResult(true, null);
+    }
+
+    public async Task<int> RecoverStaleRunningAsync(string reason, CancellationToken ct)
+    {
+        var resultText = "[stale] " + reason;
+        var now = DateTime.UtcNow;
+        await using var ctx = await _dbFactory.CreateDbContextAsync(ct);
+        return await ctx.Tasks
+            .Where(t => t.Status == TaskStatus.Running)
+            .ExecuteUpdateAsync(s => s
+                .SetProperty(t => t.Status, TaskStatus.Failed)
+                .SetProperty(t => t.FinishedAt, now)
+                .SetProperty(t => t.Result, resultText), ct);
+    }
+
+    private async Task OnChildTerminalAsync(string taskId, TaskStatus finalStatus)
+    {
+        // Terminal child writes are best-effort and use CancellationToken.None so the
+        // task lifecycle is never left partially completed because a caller cancelled.
+        string? parentId;
+        await using (var ctx = await _dbFactory.CreateDbContextAsync(CancellationToken.None))
+        {
+            parentId = await ctx.Tasks
+                .AsNoTracking()
+                .Where(t => t.Id == taskId)
+                .Select(t => t.ParentTaskId)
+                .FirstOrDefaultAsync(CancellationToken.None);
+        }
+        if (parentId is null) return;
+
+        try
+        {
+            await _chain.OnChildFinishedAsync(taskId, finalStatus, CancellationToken.None);
+        }
+        catch (Exception ex)
+        {
+            _logger.LogWarning(ex, "PlanningChain advance failed for {TaskId}", taskId);
+        }
+
+        try
+        {
+            await using var ctx = await _dbFactory.CreateDbContextAsync(CancellationToken.None);
+            await new TaskRepository(ctx).TryCompleteParentAsync(parentId, CancellationToken.None);
+        }
+        catch (Exception ex)
+        {
+            _logger.LogWarning(ex, "TryCompleteParent failed for {ParentId}", parentId);
+        }
+    }
+}
diff --git a/src/ClaudeDo.Worker/State/TransitionResult.cs b/src/ClaudeDo.Worker/State/TransitionResult.cs
new file mode 100644
index 0000000..fc7d66b
--- /dev/null
+++ b/src/ClaudeDo.Worker/State/TransitionResult.cs
@@ -0,0 +1,3 @@
+namespace ClaudeDo.Worker.State;
+
+public sealed record TransitionResult(bool Ok, string? Reason);
diff --git a/tests/ClaudeDo.Worker.Tests/External/ExternalMcpServiceTests.cs b/tests/ClaudeDo.Worker.Tests/External/ExternalMcpServiceTests.cs
index 4ab79ba..1f1ce0c 100644
--- a/tests/ClaudeDo.Worker.Tests/External/ExternalMcpServiceTests.cs
+++ b/tests/ClaudeDo.Worker.Tests/External/ExternalMcpServiceTests.cs
@@ -94,7 +94,8 @@ public sealed class ExternalMcpServiceTests : IDisposable
     // we never call its WakeQueue/RunNow/CancelTask paths, so a real QueueService
     // built with the same approach used in QueueServiceTests is sufficient.
     private ExternalMcpService BuildSut(QueueService queue) =>
-        new(_tasks, _lists, queue, _broadcaster, _tags);
+        new(_tasks, _lists, queue, _broadcaster, _tags,
+            TaskStateServiceBuilder.Build(_db.CreateFactory()).State);
 
     private QueueService CreateQueue()
     {
@@ -113,7 +114,7 @@ public sealed class ExternalMcpServiceTests : IDisposable
         var wtManager = new WorktreeManager(new GitService(), dbFactory, cfg, NullLogger<WorktreeManager>.Instance);
         var argsBuilder = new ClaudeArgsBuilder();
         var runner = new TaskRunner(fake, dbFactory, broadcaster, wtManager, argsBuilder, cfg,
-            NullLogger<TaskRunner>.Instance);
+            NullLogger<TaskRunner>.Instance, TaskStateServiceBuilder.Build(dbFactory).State);
         return new QueueService(dbFactory, runner, cfg, NullLogger<QueueService>.Instance);
     }
 
diff --git a/tests/ClaudeDo.Worker.Tests/Hub/PlanningHubTests.cs b/tests/ClaudeDo.Worker.Tests/Hub/PlanningHubTests.cs
index b0abc28..6e78a03 100644
--- a/tests/ClaudeDo.Worker.Tests/Hub/PlanningHubTests.cs
+++ b/tests/ClaudeDo.Worker.Tests/Hub/PlanningHubTests.cs
@@ -50,7 +50,7 @@ public sealed class PlanningHubTests : IDisposable
     {
         var hub = new WorkerHub(
             null!, null!, null!, null!, null!, null!, null!, null!,
-            _planning, _launcher, null!, null!);
+            _planning, _launcher, null!, null!, null!);
         hub.Clients = new FakeHubCallerClients(_proxy);
         hub.Context = new FakeHubCallerContext();
         return hub;
diff --git a/tests/ClaudeDo.Worker.Tests/Infrastructure/FakeHubContext.cs b/tests/ClaudeDo.Worker.Tests/Infrastructure/FakeHubContext.cs
new file mode 100644
index 0000000..ee89bfa
--- /dev/null
+++ b/tests/ClaudeDo.Worker.Tests/Infrastructure/FakeHubContext.cs
@@ -0,0 +1,39 @@
+using ClaudeDo.Worker.Hub;
+using Microsoft.AspNetCore.SignalR;
+
+namespace ClaudeDo.Worker.Tests.Infrastructure;
+
+public sealed record CapturedHubCall(string Method, object?[] Args);
+
+public sealed class CapturingClientProxy : IClientProxy
+{
+    public readonly List<CapturedHubCall> Calls = new();
+
+    public Task SendCoreAsync(string method, object?[] args, CancellationToken cancellationToken = default)
+    {
+        Calls.Add(new CapturedHubCall(method, args));
+        return Task.CompletedTask;
+    }
+}
+
+public sealed class CapturingHubClients : IHubClients
+{
+    public CapturingClientProxy AllProxy { get; } = new();
+    public IClientProxy All => AllProxy;
+    public IClientProxy AllExcept(IReadOnlyList<string> excludedConnectionIds) => AllProxy;
+    public IClientProxy Client(string connectionId) => AllProxy;
+    public IClientProxy Clients(IReadOnlyList<string> connectionIds) => AllProxy;
+    public IClientProxy Group(string groupName) => AllProxy;
+    public IClientProxy GroupExcept(string groupName, IReadOnlyList<string> excludedConnectionIds) => AllProxy;
+    public IClientProxy Groups(IReadOnlyList<string> groupNames) => AllProxy;
+    public IClientProxy User(string userId) => AllProxy;
+    public IClientProxy Users(IReadOnlyList<string> userIds) => AllProxy;
+}
+
+public sealed class CapturingHubContext : IHubContext<WorkerHub>
+{
+    private readonly CapturingHubClients _clients = new();
+    public CapturingClientProxy Proxy => _clients.AllProxy;
+    public IHubClients Clients => _clients;
+    public IGroupManager Groups => throw new NotImplementedException();
+}
diff --git a/tests/ClaudeDo.Worker.Tests/Infrastructure/TaskStateServiceBuilder.cs b/tests/ClaudeDo.Worker.Tests/Infrastructure/TaskStateServiceBuilder.cs
new file mode 100644
index 0000000..3551677
--- /dev/null
+++ b/tests/ClaudeDo.Worker.Tests/Infrastructure/TaskStateServiceBuilder.cs
@@ -0,0 +1,37 @@
+using ClaudeDo.Data;
+using ClaudeDo.Worker.Hub;
+using ClaudeDo.Worker.Planning;
+using ClaudeDo.Worker.State;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.Logging.Abstractions;
+
+namespace ClaudeDo.Worker.Tests.Infrastructure;
+
+/// Test-only helper that wires TaskStateService and PlanningChainCoordinator
+/// against a shared DB factory, breaking the Func cycle between them.
+public static class TaskStateServiceBuilder
+{
+    public sealed record Built(
+        TaskStateService State,
+        PlanningChainCoordinator Chain,
+        CapturingHubContext Hub,
+        Func<int> WakeCount);
+
+    public static Built Build(IDbContextFactory<ClaudeDoDbContext> dbFactory)
+    {
+        var hub = new CapturingHubContext();
+        var broadcaster = new HubBroadcaster(hub);
+        var wakeCount = new int[1];
+
+        TaskStateService? state = null;
+        var chain = new PlanningChainCoordinator(dbFactory, () => state!);
+        state = new TaskStateService(
+            dbFactory,
+            broadcaster,
+            () => Interlocked.Increment(ref wakeCount[0]),
+            chain,
+            NullLogger<TaskStateService>.Instance);
+
+        return new Built(state, chain, hub, () => Volatile.Read(ref wakeCount[0]));
+    }
+}
diff --git a/tests/ClaudeDo.Worker.Tests/Planning/PlanningChainCoordinatorTests.cs b/tests/ClaudeDo.Worker.Tests/Planning/PlanningChainCoordinatorTests.cs
index 5abea99..dc7af96 100644
--- a/tests/ClaudeDo.Worker.Tests/Planning/PlanningChainCoordinatorTests.cs
+++ b/tests/ClaudeDo.Worker.Tests/Planning/PlanningChainCoordinatorTests.cs
@@ -17,7 +17,7 @@ public sealed class PlanningChainCoordinatorTests : IDisposable
     public PlanningChainCoordinatorTests()
     {
         _factory = _db.CreateFactory();
-        _sut = new PlanningChainCoordinator(_factory);
+        _sut = TaskStateServiceBuilder.Build(_factory).Chain;
         _listId = Guid.NewGuid().ToString();
         using var ctx = _factory.CreateDbContext();
         ctx.Lists.Add(new ListEntity
diff --git a/tests/ClaudeDo.Worker.Tests/Services/QueueServiceSlotGuardTests.cs b/tests/ClaudeDo.Worker.Tests/Services/QueueServiceSlotGuardTests.cs
index 5157372..73de686 100644
--- a/tests/ClaudeDo.Worker.Tests/Services/QueueServiceSlotGuardTests.cs
+++ b/tests/ClaudeDo.Worker.Tests/Services/QueueServiceSlotGuardTests.cs
@@ -54,7 +54,7 @@ public sealed class QueueServiceSlotGuardTests : IDisposable
         var wtManager = new WorktreeManager(new ClaudeDo.Data.Git.GitService(), dbFactory, _cfg, NullLogger<WorktreeManager>.Instance);
         var argsBuilder = new ClaudeArgsBuilder();
         var runner = new TaskRunner(fake, dbFactory, broadcaster, wtManager, argsBuilder, _cfg,
-            NullLogger<TaskRunner>.Instance);
+            NullLogger<TaskRunner>.Instance, TaskStateServiceBuilder.Build(dbFactory).State);
         var service = new QueueService(dbFactory, runner, _cfg, NullLogger<QueueService>.Instance);
         return (service, fake);
     }
diff --git a/tests/ClaudeDo.Worker.Tests/Services/QueueServiceTests.cs b/tests/ClaudeDo.Worker.Tests/Services/QueueServiceTests.cs
index 3b5a88a..50410f2 100644
--- a/tests/ClaudeDo.Worker.Tests/Services/QueueServiceTests.cs
+++ b/tests/ClaudeDo.Worker.Tests/Services/QueueServiceTests.cs
@@ -55,7 +55,7 @@ public sealed class QueueServiceTests : IDisposable
         var wtManager = new WorktreeManager(new GitService(), dbFactory, _cfg, NullLogger<WorktreeManager>.Instance);
         var argsBuilder = new ClaudeArgsBuilder();
         var runner = new TaskRunner(fake, dbFactory, broadcaster, wtManager, argsBuilder, _cfg,
-            NullLogger<TaskRunner>.Instance);
+            NullLogger<TaskRunner>.Instance, TaskStateServiceBuilder.Build(dbFactory).State);
         var service = new QueueService(dbFactory, runner, _cfg, NullLogger<QueueService>.Instance);
         return (service, fake);
     }
diff --git a/tests/ClaudeDo.Worker.Tests/Services/StaleTaskRecoveryTests.cs b/tests/ClaudeDo.Worker.Tests/Services/StaleTaskRecoveryTests.cs
index f6452d6..993a513 100644
--- a/tests/ClaudeDo.Worker.Tests/Services/StaleTaskRecoveryTests.cs
+++ b/tests/ClaudeDo.Worker.Tests/Services/StaleTaskRecoveryTests.cs
@@ -54,7 +54,8 @@ public sealed class StaleTaskRecoveryTests : IDisposable
         await _tasks.AddAsync(running);
         await _tasks.AddAsync(queued);
 
-        var recovery = new StaleTaskRecovery(_db.CreateFactory(), NullLogger<StaleTaskRecovery>.Instance);
+        var built = TaskStateServiceBuilder.Build(_db.CreateFactory());
+        var recovery = new StaleTaskRecovery(built.State, NullLogger<StaleTaskRecovery>.Instance);
         await recovery.StartAsync(CancellationToken.None);
 
         var r = await _tasks.GetByIdAsync(running.Id);
diff --git a/tests/ClaudeDo.Worker.Tests/Services/TaskResetServiceTests.cs b/tests/ClaudeDo.Worker.Tests/Services/TaskResetServiceTests.cs
index 3c147d0..5ef3054 100644
--- a/tests/ClaudeDo.Worker.Tests/Services/TaskResetServiceTests.cs
+++ b/tests/ClaudeDo.Worker.Tests/Services/TaskResetServiceTests.cs
@@ -34,10 +34,12 @@ public class TaskResetServiceTests : IDisposable
     {
         var fakeHub = new RecordingHubContext();
         var broadcaster = new HubBroadcaster(fakeHub);
+        var built = TaskStateServiceBuilder.Build(db.CreateFactory());
         var svc = new TaskResetService(
             db.CreateFactory(),
             wtMgr,
             broadcaster,
+            built.State,
             NullLogger<TaskResetService>.Instance);
         return (svc, fakeHub.Proxy);
     }
@@ -111,7 +113,7 @@ public class TaskResetServiceTests : IDisposable
         {
             var updated = await new TaskRepository(ctx).GetByIdAsync(task.Id);
             Assert.NotNull(updated);
-            Assert.Equal(TaskStatus.Manual, updated!.Status);
+            Assert.Equal(TaskStatus.Idle, updated!.Status);
             Assert.Null(updated.Result);
             Assert.Null(updated.StartedAt);
             Assert.Null(updated.FinishedAt);
diff --git a/tests/ClaudeDo.Worker.Tests/State/TaskStateServiceTests.cs b/tests/ClaudeDo.Worker.Tests/State/TaskStateServiceTests.cs
new file mode 100644
index 0000000..9028cad
--- /dev/null
+++ b/tests/ClaudeDo.Worker.Tests/State/TaskStateServiceTests.cs
@@ -0,0 +1,383 @@
+using ClaudeDo.Data;
+using ClaudeDo.Data.Models;
+using ClaudeDo.Data.Repositories;
+using ClaudeDo.Worker.State;
+using ClaudeDo.Worker.Tests.Infrastructure;
+using Microsoft.EntityFrameworkCore;
+using TaskStatus = ClaudeDo.Data.Models.TaskStatus;
+
+namespace ClaudeDo.Worker.Tests.State;
+
+public sealed class TaskStateServiceTests : IDisposable
+{
+    private readonly DbFixture _db = new();
+    private readonly TestDbContextFactory _factory;
+    private readonly TaskStateServiceBuilder.Built _built;
+    private readonly ITaskStateService _sut;
+    private readonly string _listId;
+
+    public TaskStateServiceTests()
+    {
+        _factory = _db.CreateFactory();
+        _built = TaskStateServiceBuilder.Build(_factory);
+        _sut = _built.State;
+
+        _listId = Guid.NewGuid().ToString();
+        using var ctx = _factory.CreateDbContext();
+        ctx.Lists.Add(new ListEntity
+        {
+            Id = _listId,
+            Name = "Test",
+            CreatedAt = DateTime.UtcNow,
+            DefaultCommitType = "chore",
+        });
+        ctx.SaveChanges();
+    }
+
+    public void Dispose() => _db.Dispose();
+
+    private async Task<string> SeedTaskAsync(TaskStatus status, string? parentId = null, int sortOrder = 0)
+    {
+        var id = Guid.NewGuid().ToString();
+        await using var ctx = _factory.CreateDbContext();
+        ctx.Tasks.Add(new TaskEntity
+        {
+            Id = id,
+            ListId = _listId,
+            Title = "task",
+            Status = status,
+            CreatedAt = DateTime.UtcNow,
+            ParentTaskId = parentId,
+            SortOrder = sortOrder,
+        });
+        await ctx.SaveChangesAsync();
+        return id;
+    }
+
+    private async Task<TaskStatus> GetStatusAsync(string id)
+    {
+        await using var ctx = _factory.CreateDbContext();
+        return await ctx.Tasks.Where(t => t.Id == id).Select(t => t.Status).FirstAsync();
+    }
+
+    private async Task<TaskEntity> GetTaskAsync(string id)
+    {
+        await using var ctx = _factory.CreateDbContext();
+        return await new TaskRepository(ctx).GetByIdAsync(id) ?? throw new InvalidOperationException($"task {id} not found");
+    }
+
+    // ─── EnqueueAsync ─────────────────────────────────────────────────────
+
+    [Fact]
+    public async Task EnqueueAsync_FromIdle_TransitionsToQueued_AndWakesQueue()
+    {
+        var id = await SeedTaskAsync(TaskStatus.Idle);
+        var wakesBefore = _built.WakeCount();
+
+        var result = await _sut.EnqueueAsync(id, default);
+
+        Assert.True(result.Ok);
+        Assert.Equal(TaskStatus.Queued, await GetStatusAsync(id));
+        Assert.True(_built.WakeCount() > wakesBefore);
+        Assert.Contains(_built.Hub.Proxy.Calls, c => c.Method == "TaskUpdated");
+    }
+
+    [Fact]
+    public async Task EnqueueAsync_FromRunning_Rejects_AndDoesNotMutate()
+    {
+        var id = await SeedTaskAsync(TaskStatus.Running);
+
+        var result = await _sut.EnqueueAsync(id, default);
+
+        Assert.False(result.Ok);
+        Assert.Equal(TaskStatus.Running, await GetStatusAsync(id));
+    }
+
+    // ─── StartRunningAsync ────────────────────────────────────────────────
+
+    [Fact]
+    public async Task StartRunningAsync_FromQueued_TransitionsToRunning_AndStampsStartedAt()
+    {
+        var id = await SeedTaskAsync(TaskStatus.Queued);
+        var startedAt = new DateTime(2026, 4, 27, 10, 0, 0, DateTimeKind.Utc);
+
+        var result = await _sut.StartRunningAsync(id, startedAt, default);
+
+        Assert.True(result.Ok);
+        var t = await GetTaskAsync(id);
+        Assert.Equal(TaskStatus.Running, t.Status);
+        Assert.Equal(startedAt, t.StartedAt);
+    }
+
+    [Fact]
+    public async Task StartRunningAsync_FromRunning_Rejects()
+    {
+        var id = await SeedTaskAsync(TaskStatus.Running);
+
+        var result = await _sut.StartRunningAsync(id, DateTime.UtcNow, default);
+
+        Assert.False(result.Ok);
+    }
+
+    [Fact]
+    public async Task StartRunningAsync_TwoParallelClaims_ExactlyOneWins()
+    {
+        var id = await SeedTaskAsync(TaskStatus.Queued);
+        var startedAt = DateTime.UtcNow;
+
+        // Two concurrent calls: only one ExecuteUpdate should affect a row.
+        var t1 = Task.Run(() => _sut.StartRunningAsync(id, startedAt, default));
+        var t2 = Task.Run(() => _sut.StartRunningAsync(id, startedAt, default));
+        var results = await Task.WhenAll(t1, t2);
+
+        var winners = results.Count(r => r.Ok);
+        Assert.Equal(1, winners);
+        Assert.Equal(TaskStatus.Running, await GetStatusAsync(id));
+    }
+
+    // ─── CompleteAsync ────────────────────────────────────────────────────
+
+    [Fact]
+    public async Task CompleteAsync_FromRunning_TransitionsToDone()
+    {
+        var id = await SeedTaskAsync(TaskStatus.Running);
+
+        var result = await _sut.CompleteAsync(id, DateTime.UtcNow, "ok", default);
+
+        Assert.True(result.Ok);
+        var t = await GetTaskAsync(id);
+        Assert.Equal(TaskStatus.Done, t.Status);
+        Assert.Equal("ok", t.Result);
+        Assert.NotNull(t.FinishedAt);
+    }
+
+    [Fact]
+    public async Task CompleteAsync_FromQueued_Rejects()
+    {
+        var id = await SeedTaskAsync(TaskStatus.Queued);
+
+        var result = await _sut.CompleteAsync(id, DateTime.UtcNow, "ok", default);
+
+        Assert.False(result.Ok);
+        Assert.Equal(TaskStatus.Queued, await GetStatusAsync(id));
+    }
+
+    // ─── FailAsync ────────────────────────────────────────────────────────
+
+    [Fact]
+    public async Task FailAsync_FromRunning_TransitionsToFailed()
+    {
+        var id = await SeedTaskAsync(TaskStatus.Running);
+
+        var result = await _sut.FailAsync(id, DateTime.UtcNow, "boom", default);
+
+        Assert.True(result.Ok);
+        var t = await GetTaskAsync(id);
+        Assert.Equal(TaskStatus.Failed, t.Status);
+        Assert.Equal("boom", t.Result);
+    }
+
+    [Fact]
+    public async Task FailAsync_FromDone_Rejects()
+    {
+        var id = await SeedTaskAsync(TaskStatus.Done);
+
+        var result = await _sut.FailAsync(id, DateTime.UtcNow, "boom", default);
+
+        Assert.False(result.Ok);
+        Assert.Equal(TaskStatus.Done, await GetStatusAsync(id));
+    }
+
+    // ─── CancelAsync ──────────────────────────────────────────────────────
+
+    [Fact]
+    public async Task CancelAsync_FromRunning_TransitionsToCancelled()
+    {
+        var id = await SeedTaskAsync(TaskStatus.Running);
+
+        var result = await _sut.CancelAsync(id, DateTime.UtcNow, default);
+
+        Assert.True(result.Ok);
+        Assert.Equal(TaskStatus.Cancelled, await GetStatusAsync(id));
+    }
+
+    [Fact]
+    public async Task CancelAsync_FromDone_Rejects()
+    {
+        var id = await SeedTaskAsync(TaskStatus.Done);
+
+        var result = await _sut.CancelAsync(id, DateTime.UtcNow, default);
+
+        Assert.False(result.Ok);
+        Assert.Equal(TaskStatus.Done, await GetStatusAsync(id));
+    }
+
+    // ─── ResetToIdleAsync ─────────────────────────────────────────────────
+
+    [Fact]
+    public async Task ResetToIdleAsync_FromFailed_ClearsTimestamps()
+    {
+        var id = await SeedTaskAsync(TaskStatus.Failed);
+        await using (var ctx = _factory.CreateDbContext())
+        {
+            await ctx.Tasks.Where(t => t.Id == id)
+                .ExecuteUpdateAsync(s => s
+                    .SetProperty(t => t.StartedAt, DateTime.UtcNow.AddMinutes(-5))
+                    .SetProperty(t => t.FinishedAt, DateTime.UtcNow.AddMinutes(-1))
+                    .SetProperty(t => t.Result, "old"));
+        }
+
+        var result = await _sut.ResetToIdleAsync(id, default);
+
+        Assert.True(result.Ok);
+        var t = await GetTaskAsync(id);
+        Assert.Equal(TaskStatus.Idle, t.Status);
+        Assert.Null(t.StartedAt);
+        Assert.Null(t.FinishedAt);
+        Assert.Null(t.Result);
+    }
+
+    [Fact]
+    public async Task ResetToIdleAsync_FromRunning_Rejects()
+    {
+        var id = await SeedTaskAsync(TaskStatus.Running);
+
+        var result = await _sut.ResetToIdleAsync(id, default);
+
+        Assert.False(result.Ok);
+        Assert.Equal(TaskStatus.Running, await GetStatusAsync(id));
+    }
+
+    // ─── StartPlanningAsync ───────────────────────────────────────────────
+
+    [Fact]
+    public async Task StartPlanningAsync_FromManual_FlipsStatus_AndPlanningPhase()
+    {
+        var id = await SeedTaskAsync(TaskStatus.Manual);
+
+        var result = await _sut.StartPlanningAsync(id, default);
+
+        Assert.True(result.Ok);
+        var t = await GetTaskAsync(id);
+        Assert.Equal(TaskStatus.Planning, t.Status);
+        Assert.Equal(PlanningPhase.Active, t.PlanningPhase);
+    }
+
+    [Fact]
+    public async Task StartPlanningAsync_FromRunning_Rejects()
+    {
+        var id = await SeedTaskAsync(TaskStatus.Running);
+
+        var result = await _sut.StartPlanningAsync(id, default);
+
+        Assert.False(result.Ok);
+    }
+
+    // ─── FinalizePlanningAsync ────────────────────────────────────────────
+
+    [Fact]
+    public async Task FinalizePlanningAsync_OnActivePhase_TransitionsToFinalized()
+    {
+        var id = await SeedTaskAsync(TaskStatus.Manual);
+        await _sut.StartPlanningAsync(id, default);
+
+        var result = await _sut.FinalizePlanningAsync(id, default);
+
+        Assert.True(result.Ok);
+        var t = await GetTaskAsync(id);
+        Assert.Equal(PlanningPhase.Finalized, t.PlanningPhase);
+        Assert.NotNull(t.PlanningFinalizedAt);
+    }
+
+    [Fact]
+    public async Task FinalizePlanningAsync_OnNonePhase_Rejects()
+    {
+        var id = await SeedTaskAsync(TaskStatus.Manual);
+
+        var result = await _sut.FinalizePlanningAsync(id, default);
+
+        Assert.False(result.Ok);
+    }
+
+    // ─── BlockOnAsync / UnblockAsync ─────────────────────────────────────
+
+    [Fact]
+    public async Task BlockOnAsync_SetsBlockedByTaskId()
+    {
+        var pred = await SeedTaskAsync(TaskStatus.Queued);
+        var task = await SeedTaskAsync(TaskStatus.Queued);
+
+        var result = await _sut.BlockOnAsync(task, pred, default);
+
+        Assert.True(result.Ok);
+        var t = await GetTaskAsync(task);
+        Assert.Equal(pred, t.BlockedByTaskId);
+    }
+
+    [Fact]
+    public async Task UnblockAsync_ClearsBlockedByTaskId_AndWakesQueue()
+    {
+        var pred = await SeedTaskAsync(TaskStatus.Queued);
+        var task = await SeedTaskAsync(TaskStatus.Queued);
+        await _sut.BlockOnAsync(task, pred, default);
+        var wakesBefore = _built.WakeCount();
+
+        var result = await _sut.UnblockAsync(task, default);
+
+        Assert.True(result.Ok);
+        var t = await GetTaskAsync(task);
+        Assert.Null(t.BlockedByTaskId);
+        Assert.True(_built.WakeCount() > wakesBefore);
+    }
+
+    [Fact]
+    public async Task UnblockAsync_OnWaitingTask_FlipsToQueued()
+    {
+        // Bridge to legacy chain layout: a Status=Waiting sibling becomes Queued on unblock.
+        var task = await SeedTaskAsync(TaskStatus.Waiting);
+
+        var result = await _sut.UnblockAsync(task, default);
+
+        Assert.True(result.Ok);
+        Assert.Equal(TaskStatus.Queued, await GetStatusAsync(task));
+    }
+
+    // ─── RecoverStaleRunningAsync ─────────────────────────────────────────
+
+    [Fact]
+    public async Task RecoverStaleRunningAsync_FlipsAllRunningToFailed_ReturnsCount()
+    {
+        var r1 = await SeedTaskAsync(TaskStatus.Running);
+        var r2 = await SeedTaskAsync(TaskStatus.Running);
+        var q = await SeedTaskAsync(TaskStatus.Queued);
+
+        var count = await _sut.RecoverStaleRunningAsync("worker restart", default);
+
+        Assert.Equal(2, count);
+        Assert.Equal(TaskStatus.Failed, await GetStatusAsync(r1));
+        Assert.Equal(TaskStatus.Failed, await GetStatusAsync(r2));
+        Assert.Equal(TaskStatus.Queued, await GetStatusAsync(q));
+        var t = await GetTaskAsync(r1);
+        Assert.StartsWith("[stale] ", t.Result);
+    }
+
+    // ─── Child terminal → chain advance ───────────────────────────────────
+
+    [Fact]
+    public async Task CompleteAsync_OnChild_AdvancesNextWaitingSibling()
+    {
+        var parent = await SeedTaskAsync(TaskStatus.Planned);
+        var c0 = await SeedTaskAsync(TaskStatus.Running, parentId: parent, sortOrder: 0);
+        var c1 = await SeedTaskAsync(TaskStatus.Waiting, parentId: parent, sortOrder: 1);
+        var c2 = await SeedTaskAsync(TaskStatus.Waiting, parentId: parent, sortOrder: 2);
+
+        var result = await _sut.CompleteAsync(c0, DateTime.UtcNow, "ok", default);
+
+        Assert.True(result.Ok);
+        Assert.Equal(TaskStatus.Done, await GetStatusAsync(c0));
+        // Next sibling was Waiting → chain coordinator unblocks → Queued.
+        Assert.Equal(TaskStatus.Queued, await GetStatusAsync(c1));
+        // Subsequent sibling untouched.
+        Assert.Equal(TaskStatus.Waiting, await GetStatusAsync(c2));
+    }
+}