feat(worker): add claude-cli runner, queue service, and hub api

Runner stack (non-worktree path): IClaudeProcess + ClaudeProcess spawning the
CLI with --output-format stream-json, prompt via stdin, parses the final
type:"result" line into RunResult. LogWriter appends ndjson to
~/.todo-app/logs/<taskId>.ndjson. TaskRunner orchestrates DB transitions
(MarkRunning -> MarkDone/Failed) and pushes TaskStarted/Message/Finished/
Updated via HubBroadcaster. Worktree-backed lists short-circuit with a
"Slice E" failure message until git support lands.

QueueService (BackgroundService) holds two in-memory slots (_queueSlot +
_overrideSlot) guarded by a lock. Uses PeriodicTimer + SemaphoreSlim wake
signal so WakeQueue() triggers an instant pickup. RunNow throws
InvalidOperationException when override busy; CancelTask cancels the linked
CTS which kills the child process tree.

WorkerHub extended with GetActive, RunNow (translated to HubException
variants), CancelTask, WakeQueue. HubBroadcaster exposes typed push methods.

Tests: 26 pass (12 new). QueueServiceTests cover override-busy,
schedule-filter, FIFO sequentiality, cancellation, plus a FakeClaudeProcess
that blocks on a TCS for deterministic slot-state assertions.
MessageParserTests cover result extraction + malformed/non-result lines.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/ClaudeDo.Worker/Runner/TaskRunner.cs

@@ -0,0 +1,123 @@
+using ClaudeDo.Data.Repositories;
+using ClaudeDo.Worker.Config;
+using ClaudeDo.Worker.Hub;
+
+namespace ClaudeDo.Worker.Runner;
+
+public sealed class TaskRunner
+{
+    private readonly IClaudeProcess _claude;
+    private readonly TaskRepository _taskRepo;
+    private readonly ListRepository _listRepo;
+    private readonly HubBroadcaster _broadcaster;
+    private readonly WorkerConfig _cfg;
+    private readonly ILogger<TaskRunner> _logger;
+
+    public TaskRunner(
+        IClaudeProcess claude,
+        TaskRepository taskRepo,
+        ListRepository listRepo,
+        HubBroadcaster broadcaster,
+        WorkerConfig cfg,
+        ILogger<TaskRunner> logger)
+    {
+        _claude = claude;
+        _taskRepo = taskRepo;
+        _listRepo = listRepo;
+        _broadcaster = broadcaster;
+        _cfg = cfg;
+        _logger = logger;
+    }
+
+    public async Task RunAsync(Data.Models.TaskEntity task, string slot, CancellationToken ct)
+    {
+        try
+        {
+            var list = await _listRepo.GetByIdAsync(task.ListId, ct);
+            if (list is null)
+            {
+                await MarkFailed(task.Id, slot, "List not found.");
+                return;
+            }
+
+            // Slice D: worktree mode not yet implemented.
+            if (list.WorkingDir is not null)
+            {
+                await MarkFailed(task.Id, slot, "Worktree mode not implemented yet (Slice E)");
+                return;
+            }
+
+            // Non-worktree sandbox path.
+            var sandboxDir = Path.Combine(_cfg.SandboxRoot, task.Id);
+            Directory.CreateDirectory(sandboxDir);
+
+            var logPath = Path.Combine(_cfg.LogRoot, $"{task.Id}.ndjson");
+
+            await _taskRepo.SetLogPathAsync(task.Id, logPath, ct);
+            var now = DateTime.UtcNow;
+            await _taskRepo.MarkRunningAsync(task.Id, now, ct);
+            await _broadcaster.TaskStarted(slot, task.Id, now);
+
+            // Build prompt.
+            var prompt = string.IsNullOrWhiteSpace(task.Description)
+                ? task.Title
+                : $"{task.Title}\n\n{task.Description.Trim()}";
+
+            await using var logWriter = new LogWriter(logPath);
+
+            var result = await _claude.RunAsync(
+                prompt,
+                sandboxDir,
+                logPath,
+                task.Id,
+                async line =>
+                {
+                    await logWriter.WriteLineAsync(line, ct);
+                    await _broadcaster.TaskMessage(task.Id, line);
+                },
+                ct);
+
+            var finishedAt = DateTime.UtcNow;
+
+            if (result.IsSuccess)
+            {
+                await _taskRepo.MarkDoneAsync(task.Id, finishedAt, result.ResultMarkdown, ct);
+                await _broadcaster.TaskFinished(slot, task.Id, "done", finishedAt);
+                _logger.LogInformation("Task {TaskId} completed successfully", task.Id);
+            }
+            else
+            {
+                await _taskRepo.MarkFailedAsync(task.Id, finishedAt, result.ErrorMarkdown, ct);
+                await _broadcaster.TaskFinished(slot, task.Id, "failed", finishedAt);
+                _logger.LogWarning("Task {TaskId} failed: {Error}", task.Id, result.ErrorMarkdown);
+            }
+
+            await _broadcaster.TaskUpdated(task.Id);
+        }
+        catch (OperationCanceledException)
+        {
+            _logger.LogInformation("Task {TaskId} was cancelled", task.Id);
+            await MarkFailed(task.Id, slot, "Task cancelled.");
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Unhandled exception running task {TaskId}", task.Id);
+            await MarkFailed(task.Id, slot, $"Unhandled error: {ex.Message}");
+        }
+    }
+
+    private async Task MarkFailed(string taskId, string slot, string error)
+    {
+        try
+        {
+            var now = DateTime.UtcNow;
+            await _taskRepo.MarkFailedAsync(taskId, now, error);
+            await _broadcaster.TaskFinished(slot, taskId, "failed", now);
+            await _broadcaster.TaskUpdated(taskId);
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Failed to mark task {TaskId} as failed", taskId);
+        }
+    }
+}