diff --git a/src/ClaudeDo.Data/Repositories/TagRepository.cs b/src/ClaudeDo.Data/Repositories/TagRepository.cs
index d73d9b7..d15fa0e 100644
--- a/src/ClaudeDo.Data/Repositories/TagRepository.cs
+++ b/src/ClaudeDo.Data/Repositories/TagRepository.cs
@@ -1,3 +1,4 @@
+using ClaudeDo.Data.Models;
 using Microsoft.Data.Sqlite;
 
 namespace ClaudeDo.Data.Repositories;
@@ -8,6 +9,19 @@ public sealed class TagRepository
 
     public TagRepository(SqliteConnectionFactory factory) => _factory = factory;
 
+    public async Task<List<TagEntity>> GetAllAsync(CancellationToken ct = default)
+    {
+        await using var conn = _factory.Open();
+        await using var cmd = conn.CreateCommand();
+        cmd.CommandText = "SELECT id, name FROM tags ORDER BY id";
+
+        await using var reader = await cmd.ExecuteReaderAsync(ct);
+        var result = new List<TagEntity>();
+        while (await reader.ReadAsync(ct))
+            result.Add(new TagEntity { Id = reader.GetInt64(0), Name = reader.GetString(1) });
+        return result;
+    }
+
     public async Task<long> GetOrCreateAsync(string name, CancellationToken ct = default)
     {
         await using var conn = _factory.Open();
diff --git a/src/ClaudeDo.Data/Repositories/TaskRepository.cs b/src/ClaudeDo.Data/Repositories/TaskRepository.cs
index 5bbb404..8db5b23 100644
--- a/src/ClaudeDo.Data/Repositories/TaskRepository.cs
+++ b/src/ClaudeDo.Data/Repositories/TaskRepository.cs
@@ -202,6 +202,16 @@ public sealed class TaskRepository
 
     #region Transitions
 
+    public async Task SetLogPathAsync(string taskId, string logPath, CancellationToken ct = default)
+    {
+        await using var conn = _factory.Open();
+        await using var cmd = conn.CreateCommand();
+        cmd.CommandText = "UPDATE tasks SET log_path = @log_path WHERE id = @id";
+        cmd.Parameters.AddWithValue("@id", taskId);
+        cmd.Parameters.AddWithValue("@log_path", logPath);
+        await cmd.ExecuteNonQueryAsync(ct);
+    }
+
     public async Task MarkRunningAsync(string taskId, DateTime startedAt, CancellationToken ct = default)
     {
         await using var conn = _factory.Open();
diff --git a/src/ClaudeDo.Worker/Hub/HubBroadcaster.cs b/src/ClaudeDo.Worker/Hub/HubBroadcaster.cs
new file mode 100644
index 0000000..d46d4bb
--- /dev/null
+++ b/src/ClaudeDo.Worker/Hub/HubBroadcaster.cs
@@ -0,0 +1,25 @@
+using Microsoft.AspNetCore.SignalR;
+
+namespace ClaudeDo.Worker.Hub;
+
+public sealed class HubBroadcaster
+{
+    private readonly IHubContext<WorkerHub> _hub;
+
+    public HubBroadcaster(IHubContext<WorkerHub> hub) => _hub = hub;
+
+    public Task TaskStarted(string slot, string taskId, DateTime startedAt) =>
+        _hub.Clients.All.SendAsync("TaskStarted", slot, taskId, startedAt);
+
+    public Task TaskFinished(string slot, string taskId, string status, DateTime finishedAt) =>
+        _hub.Clients.All.SendAsync("TaskFinished", slot, taskId, status, finishedAt);
+
+    public Task TaskMessage(string taskId, string ndjsonLine) =>
+        _hub.Clients.All.SendAsync("TaskMessage", taskId, ndjsonLine);
+
+    public Task WorktreeUpdated(string taskId) =>
+        _hub.Clients.All.SendAsync("WorktreeUpdated", taskId);
+
+    public Task TaskUpdated(string taskId) =>
+        _hub.Clients.All.SendAsync("TaskUpdated", taskId);
+}
diff --git a/src/ClaudeDo.Worker/Hub/WorkerHub.cs b/src/ClaudeDo.Worker/Hub/WorkerHub.cs
index 24d32ab..6acbea3 100644
--- a/src/ClaudeDo.Worker/Hub/WorkerHub.cs
+++ b/src/ClaudeDo.Worker/Hub/WorkerHub.cs
@@ -1,16 +1,44 @@
 using System.Reflection;
+using ClaudeDo.Worker.Services;
 using Microsoft.AspNetCore.SignalR;
 
 namespace ClaudeDo.Worker.Hub;
 
-/// <summary>
-/// SignalR hub the UI connects to. Only <see cref="Ping"/> is implemented at this stage;
-/// RunNow/CancelTask/WakeQueue/GetActive land here once QueueService exists.
-/// </summary>
 public sealed class WorkerHub : Microsoft.AspNetCore.SignalR.Hub
 {
     private static readonly string Version =
         Assembly.GetExecutingAssembly().GetName().Version?.ToString(3) ?? "0.0.0";
 
+    private readonly QueueService _queue;
+
+    public WorkerHub(QueueService queue) => _queue = queue;
+
     public string Ping() => $"pong v{Version}";
+
+    public IReadOnlyList<object> GetActive()
+    {
+        return _queue.GetActive()
+            .Select(a => (object)new { slot = a.slot, taskId = a.taskId, startedAt = a.startedAt })
+            .ToList();
+    }
+
+    public async Task RunNow(string taskId)
+    {
+        try
+        {
+            await _queue.RunNow(taskId);
+        }
+        catch (InvalidOperationException)
+        {
+            throw new HubException("override slot busy");
+        }
+        catch (KeyNotFoundException)
+        {
+            throw new HubException("task not found");
+        }
+    }
+
+    public bool CancelTask(string taskId) => _queue.CancelTask(taskId);
+
+    public void WakeQueue() => _queue.WakeQueue();
 }
diff --git a/src/ClaudeDo.Worker/Program.cs b/src/ClaudeDo.Worker/Program.cs
index a3e06ac..0f3d109 100644
--- a/src/ClaudeDo.Worker/Program.cs
+++ b/src/ClaudeDo.Worker/Program.cs
@@ -2,6 +2,7 @@ using ClaudeDo.Data;
 using ClaudeDo.Data.Repositories;
 using ClaudeDo.Worker.Config;
 using ClaudeDo.Worker.Hub;
+using ClaudeDo.Worker.Runner;
 using ClaudeDo.Worker.Services;
 
 var cfg = WorkerConfig.Load();
@@ -21,6 +22,15 @@ builder.Services.AddSingleton<WorktreeRepository>();
 builder.Services.AddHostedService<StaleTaskRecovery>();
 builder.Services.AddSignalR();
 
+// Runner stack.
+builder.Services.AddSingleton<IClaudeProcess, ClaudeProcess>();
+builder.Services.AddSingleton<HubBroadcaster>();
+builder.Services.AddSingleton<TaskRunner>();
+
+// QueueService: singleton + hosted service (same instance).
+builder.Services.AddSingleton<QueueService>();
+builder.Services.AddHostedService(sp => sp.GetRequiredService<QueueService>());
+
 // Loopback-only bind. Firewall is irrelevant for 127.0.0.1.
 builder.WebHost.UseUrls($"http://127.0.0.1:{cfg.SignalRPort}");
 
diff --git a/src/ClaudeDo.Worker/Runner/ClaudeProcess.cs b/src/ClaudeDo.Worker/Runner/ClaudeProcess.cs
new file mode 100644
index 0000000..1a4d0a5
--- /dev/null
+++ b/src/ClaudeDo.Worker/Runner/ClaudeProcess.cs
@@ -0,0 +1,96 @@
+using System.Diagnostics;
+using System.Text;
+using ClaudeDo.Worker.Config;
+
+namespace ClaudeDo.Worker.Runner;
+
+public sealed class ClaudeProcess : IClaudeProcess
+{
+    private readonly WorkerConfig _cfg;
+    private readonly ILogger<ClaudeProcess> _logger;
+
+    public ClaudeProcess(WorkerConfig cfg, ILogger<ClaudeProcess> logger)
+    {
+        _cfg = cfg;
+        _logger = logger;
+    }
+
+    public async Task<RunResult> RunAsync(
+        string prompt,
+        string workingDirectory,
+        string logPath,
+        string taskId,
+        Func<string, Task> onStdoutLine,
+        CancellationToken ct)
+    {
+        var psi = new ProcessStartInfo
+        {
+            FileName = _cfg.ClaudeBin,
+            Arguments = "-p --output-format stream-json --verbose --dangerously-skip-permissions",
+            WorkingDirectory = workingDirectory,
+            RedirectStandardInput = true,
+            RedirectStandardOutput = true,
+            RedirectStandardError = true,
+            UseShellExecute = false,
+            CreateNoWindow = true,
+            StandardOutputEncoding = Encoding.UTF8,
+            StandardErrorEncoding = Encoding.UTF8,
+        };
+
+        using var process = new Process { StartInfo = psi };
+        process.Start();
+
+        // Write prompt to stdin, then close.
+        await process.StandardInput.WriteAsync(prompt);
+        process.StandardInput.Close();
+
+        string? resultMarkdown = null;
+        var lastStderr = new StringBuilder();
+
+        // Register cancellation to kill the process tree.
+        await using var ctr = ct.Register(() =>
+        {
+            try { process.Kill(entireProcessTree: true); }
+            catch { /* already exited */ }
+        });
+
+        // Read stdout and stderr concurrently.
+        var stdoutTask = Task.Run(async () =>
+        {
+            while (await process.StandardOutput.ReadLineAsync(ct) is { } line)
+            {
+                if (string.IsNullOrEmpty(line)) continue;
+                await onStdoutLine(line);
+
+                if (MessageParser.TryExtractResult(line, out var res))
+                    resultMarkdown = res;
+            }
+        }, ct);
+
+        var stderrTask = Task.Run(async () =>
+        {
+            while (await process.StandardError.ReadLineAsync(ct) is { } line)
+            {
+                if (string.IsNullOrEmpty(line)) continue;
+                lastStderr.AppendLine(line);
+                await onStdoutLine($"[stderr] {line}");
+            }
+        }, ct);
+
+        await Task.WhenAll(stdoutTask, stderrTask);
+        await process.WaitForExitAsync(ct);
+
+        var exitCode = process.ExitCode;
+
+        if (exitCode == 0 && resultMarkdown is not null)
+        {
+            return new RunResult { ExitCode = exitCode, ResultMarkdown = resultMarkdown };
+        }
+
+        var error = lastStderr.Length > 0
+            ? lastStderr.ToString().Trim()
+            : $"Claude exited with code {exitCode} and no result.";
+
+        return new RunResult { ExitCode = exitCode, ErrorMarkdown = error };
+    }
+}
diff --git a/src/ClaudeDo.Worker/Runner/IClaudeProcess.cs b/src/ClaudeDo.Worker/Runner/IClaudeProcess.cs
new file mode 100644
index 0000000..e3fb057
--- /dev/null
+++ b/src/ClaudeDo.Worker/Runner/IClaudeProcess.cs
@@ -0,0 +1,12 @@
+namespace ClaudeDo.Worker.Runner;
+
+public interface IClaudeProcess
+{
+    Task<RunResult> RunAsync(
+        string prompt,
+        string workingDirectory,
+        string logPath,
+        string taskId,
+        Func<string, Task> onStdoutLine,
+        CancellationToken ct);
+}
diff --git a/src/ClaudeDo.Worker/Runner/LogWriter.cs b/src/ClaudeDo.Worker/Runner/LogWriter.cs
new file mode 100644
index 0000000..a49b35c
--- /dev/null
+++ b/src/ClaudeDo.Worker/Runner/LogWriter.cs
@@ -0,0 +1,26 @@
+namespace ClaudeDo.Worker.Runner;
+
+public sealed class LogWriter : IAsyncDisposable
+{
+    private readonly StreamWriter _writer;
+
+    public LogWriter(string filePath)
+    {
+        var dir = Path.GetDirectoryName(filePath);
+        if (dir is not null)
+            Directory.CreateDirectory(dir);
+
+        _writer = new StreamWriter(filePath, append: true) { AutoFlush = true };
+    }
+
+    public async Task WriteLineAsync(string line, CancellationToken ct = default)
+    {
+        ct.ThrowIfCancellationRequested();
+        await _writer.WriteLineAsync(line.AsMemory(), ct);
+    }
+
+    public async ValueTask DisposeAsync()
+    {
+        await _writer.DisposeAsync();
+    }
+}
diff --git a/src/ClaudeDo.Worker/Runner/MessageParser.cs b/src/ClaudeDo.Worker/Runner/MessageParser.cs
new file mode 100644
index 0000000..9343569
--- /dev/null
+++ b/src/ClaudeDo.Worker/Runner/MessageParser.cs
@@ -0,0 +1,33 @@
+using System.Text.Json;
+
+namespace ClaudeDo.Worker.Runner;
+
+public static class MessageParser
+{
+    public static bool TryExtractResult(string ndjsonLine, out string? result)
+    {
+        result = null;
+        if (string.IsNullOrWhiteSpace(ndjsonLine))
+            return false;
+
+        try
+        {
+            using var doc = JsonDocument.Parse(ndjsonLine);
+            var root = doc.RootElement;
+
+            if (root.TryGetProperty("type", out var typeProp) &&
+                typeProp.GetString() == "result" &&
+                root.TryGetProperty("result", out var resultProp))
+            {
+                result = resultProp.GetString();
+                return true;
+            }
+        }
+        catch (JsonException)
+        {
+            // Malformed JSON — not a result line.
+        }
+
+        return false;
+    }
+}
diff --git a/src/ClaudeDo.Worker/Runner/RunResult.cs b/src/ClaudeDo.Worker/Runner/RunResult.cs
new file mode 100644
index 0000000..bed0cff
--- /dev/null
+++ b/src/ClaudeDo.Worker/Runner/RunResult.cs
@@ -0,0 +1,10 @@
+namespace ClaudeDo.Worker.Runner;
+
+public sealed class RunResult
+{
+    public required int ExitCode { get; init; }
+    public string? ResultMarkdown { get; init; }
+    public string? ErrorMarkdown { get; init; }
+
+    public bool IsSuccess => ExitCode == 0 && ResultMarkdown is not null;
+}
diff --git a/src/ClaudeDo.Worker/Runner/TaskRunner.cs b/src/ClaudeDo.Worker/Runner/TaskRunner.cs
new file mode 100644
index 0000000..93f3f0e
--- /dev/null
+++ b/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);
+        }
+    }
+}
diff --git a/src/ClaudeDo.Worker/Services/QueueService.cs b/src/ClaudeDo.Worker/Services/QueueService.cs
new file mode 100644
index 0000000..19f8bed
--- /dev/null
+++ b/src/ClaudeDo.Worker/Services/QueueService.cs
@@ -0,0 +1,162 @@
+using ClaudeDo.Data.Models;
+using ClaudeDo.Data.Repositories;
+using ClaudeDo.Worker.Config;
+using ClaudeDo.Worker.Runner;
+
+namespace ClaudeDo.Worker.Services;
+
+public sealed class QueueSlotState
+{
+    public required string TaskId { get; init; }
+    public required DateTime StartedAt { get; init; }
+    public required CancellationTokenSource Cts { get; init; }
+}
+
+public sealed class QueueService : BackgroundService
+{
+    private readonly TaskRepository _taskRepo;
+    private readonly TaskRunner _runner;
+    private readonly WorkerConfig _cfg;
+    private readonly ILogger<QueueService> _logger;
+
+    private readonly object _lock = new();
+    private volatile QueueSlotState? _queueSlot;
+    private volatile QueueSlotState? _overrideSlot;
+
+    private readonly SemaphoreSlim _wakeSignal = new(0, 1);
+
+    public QueueService(
+        TaskRepository taskRepo,
+        TaskRunner runner,
+        WorkerConfig cfg,
+        ILogger<QueueService> logger)
+    {
+        _taskRepo = taskRepo;
+        _runner = runner;
+        _cfg = cfg;
+        _logger = logger;
+    }
+
+    public IReadOnlyList<(string slot, string taskId, DateTime startedAt)> GetActive()
+    {
+        var list = new List<(string, string, DateTime)>();
+        var q = _queueSlot;
+        if (q is not null) list.Add(("queue", q.TaskId, q.StartedAt));
+        var o = _overrideSlot;
+        if (o is not null) list.Add(("override", o.TaskId, o.StartedAt));
+        return list;
+    }
+
+    public void WakeQueue()
+    {
+        // Release if not already signalled.
+        try { _wakeSignal.Release(); }
+        catch (SemaphoreFullException) { /* already signalled */ }
+    }
+
+    public async Task RunNow(string taskId)
+    {
+        var task = await _taskRepo.GetByIdAsync(taskId);
+        if (task is null)
+            throw new KeyNotFoundException($"Task '{taskId}' not found.");
+
+        lock (_lock)
+        {
+            if (_overrideSlot is not null)
+                throw new InvalidOperationException("override slot busy");
+
+            var cts = new CancellationTokenSource();
+            _overrideSlot = new QueueSlotState { TaskId = taskId, StartedAt = DateTime.UtcNow, Cts = cts };
+
+            _ = RunInSlotAsync(task, "override", cts.Token).ContinueWith(_ =>
+            {
+                lock (_lock) { _overrideSlot = null; }
+            }, TaskScheduler.Default);
+        }
+    }
+
+    public bool CancelTask(string taskId)
+    {
+        lock (_lock)
+        {
+            if (_queueSlot is not null && _queueSlot.TaskId == taskId)
+            {
+                _queueSlot.Cts.Cancel();
+                return true;
+            }
+            if (_overrideSlot is not null && _overrideSlot.TaskId == taskId)
+            {
+                _overrideSlot.Cts.Cancel();
+                return true;
+            }
+        }
+        return false;
+    }
+
+    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    {
+        _logger.LogInformation("QueueService started");
+
+        using var timer = new PeriodicTimer(TimeSpan.FromMilliseconds(_cfg.QueueBackstopIntervalMs));
+
+        while (!stoppingToken.IsCancellationRequested)
+        {
+            try
+            {
+                // Wait for wake signal or backstop timer.
+                var wakeTask = _wakeSignal.WaitAsync(stoppingToken);
+                var timerTask = timer.WaitForNextTickAsync(stoppingToken).AsTask();
+
+                await Task.WhenAny(wakeTask, timerTask);
+
+                // Drain wake signal if it fired.
+                if (wakeTask.IsCompletedSuccessfully)
+                {
+                    // Good — signal consumed.
+                }
+
+                if (_queueSlot is not null) continue;
+
+                var task = await _taskRepo.GetNextQueuedAgentTaskAsync(DateTime.UtcNow, stoppingToken);
+                if (task is null) continue;
+
+                lock (_lock)
+                {
+                    if (_queueSlot is not null) continue;
+
+                    var cts = CancellationTokenSource.CreateLinkedTokenSource(stoppingToken);
+                    _queueSlot = new QueueSlotState { TaskId = task.Id, StartedAt = DateTime.UtcNow, Cts = cts };
+
+                    _ = RunInSlotAsync(task, "queue", cts.Token).ContinueWith(_ =>
+                    {
+                        lock (_lock) { _queueSlot = null; }
+                        WakeQueue(); // Check for next task immediately.
+                    }, TaskScheduler.Default);
+                }
+            }
+            catch (OperationCanceledException) when (stoppingToken.IsCancellationRequested)
+            {
+                break;
+            }
+            catch (Exception ex)
+            {
+                _logger.LogError(ex, "QueueService loop error");
+            }
+        }
+
+        _logger.LogInformation("QueueService stopping");
+    }
+
+    private async Task RunInSlotAsync(TaskEntity task, string slot, CancellationToken ct)
+    {
+        try
+        {
+            _logger.LogInformation("Starting task {TaskId} in {Slot} slot", task.Id, slot);
+            await _runner.RunAsync(task, slot, ct);
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Slot runner error for task {TaskId}", task.Id);
+        }
+    }
+}
diff --git a/tests/ClaudeDo.Worker.Tests/Runner/MessageParserTests.cs b/tests/ClaudeDo.Worker.Tests/Runner/MessageParserTests.cs
new file mode 100644
index 0000000..56b4faf
--- /dev/null
+++ b/tests/ClaudeDo.Worker.Tests/Runner/MessageParserTests.cs
@@ -0,0 +1,53 @@
+using ClaudeDo.Worker.Runner;
+
+namespace ClaudeDo.Worker.Tests.Runner;
+
+public sealed class MessageParserTests
+{
+    [Fact]
+    public void WellFormed_Result_Line_Extracts_Result()
+    {
+        var line = """{"type":"result","result":"Hello **world**"}""";
+        Assert.True(MessageParser.TryExtractResult(line, out var result));
+        Assert.Equal("Hello **world**", result);
+    }
+
+    [Fact]
+    public void Non_Result_Type_Returns_False()
+    {
+        var line = """{"type":"assistant","message":"hi"}""";
+        Assert.False(MessageParser.TryExtractResult(line, out var result));
+        Assert.Null(result);
+    }
+
+    [Fact]
+    public void Missing_Type_Property_Returns_False()
+    {
+        var line = """{"result":"data"}""";
+        Assert.False(MessageParser.TryExtractResult(line, out var result));
+        Assert.Null(result);
+    }
+
+    [Fact]
+    public void Malformed_Json_Returns_False_No_Throw()
+    {
+        var line = "this is not json {{{";
+        Assert.False(MessageParser.TryExtractResult(line, out var result));
+        Assert.Null(result);
+    }
+
+    [Fact]
+    public void Empty_Line_Returns_False()
+    {
+        Assert.False(MessageParser.TryExtractResult("", out _));
+        Assert.False(MessageParser.TryExtractResult("   ", out _));
+    }
+
+    [Fact]
+    public void Null_Result_Value_Returns_True_With_Null()
+    {
+        var line = """{"type":"result","result":null}""";
+        Assert.True(MessageParser.TryExtractResult(line, out var result));
+        Assert.Null(result);
+    }
+}
diff --git a/tests/ClaudeDo.Worker.Tests/Services/QueueServiceTests.cs b/tests/ClaudeDo.Worker.Tests/Services/QueueServiceTests.cs
new file mode 100644
index 0000000..7a4e7e6
--- /dev/null
+++ b/tests/ClaudeDo.Worker.Tests/Services/QueueServiceTests.cs
@@ -0,0 +1,278 @@
+using ClaudeDo.Data.Models;
+using ClaudeDo.Data.Repositories;
+using ClaudeDo.Worker.Config;
+using ClaudeDo.Worker.Hub;
+using ClaudeDo.Worker.Runner;
+using ClaudeDo.Worker.Services;
+using ClaudeDo.Worker.Tests.Infrastructure;
+using Microsoft.AspNetCore.SignalR;
+using Microsoft.Extensions.Logging.Abstractions;
+using TaskStatus = ClaudeDo.Data.Models.TaskStatus;
+
+namespace ClaudeDo.Worker.Tests.Services;
+
+public sealed class QueueServiceTests : IDisposable
+{
+    private readonly DbFixture _db = new();
+    private readonly TaskRepository _taskRepo;
+    private readonly ListRepository _listRepo;
+    private readonly TagRepository _tagRepo;
+    private readonly WorkerConfig _cfg;
+    private readonly string _tempDir;
+
+    public QueueServiceTests()
+    {
+        _taskRepo = new TaskRepository(_db.Factory);
+        _listRepo = new ListRepository(_db.Factory);
+        _tagRepo = new TagRepository(_db.Factory);
+        _tempDir = Path.Combine(Path.GetTempPath(), $"claudedo_test_{Guid.NewGuid():N}");
+        Directory.CreateDirectory(_tempDir);
+        _cfg = new WorkerConfig
+        {
+            SandboxRoot = Path.Combine(_tempDir, "sandbox"),
+            LogRoot = Path.Combine(_tempDir, "logs"),
+            QueueBackstopIntervalMs = 50, // fast for tests
+        };
+    }
+
+    public void Dispose()
+    {
+        _db.Dispose();
+        try { Directory.Delete(_tempDir, true); } catch { }
+    }
+
+    private (QueueService service, FakeClaudeProcess fakeProcess) CreateService(
+        Func<string, string, string, string, Func<string, Task>, CancellationToken, Task<RunResult>>? handler = null)
+    {
+        var fake = new FakeClaudeProcess(handler);
+        var broadcaster = new HubBroadcaster(new FakeHubContext());
+        var runner = new TaskRunner(fake, _taskRepo, _listRepo, broadcaster, _cfg,
+            NullLogger<TaskRunner>.Instance);
+        var service = new QueueService(_taskRepo, runner, _cfg, NullLogger<QueueService>.Instance);
+        return (service, fake);
+    }
+
+    private async Task<(string listId, long agentTagId)> SeedListWithAgentTag()
+    {
+        var listId = Guid.NewGuid().ToString();
+        await _listRepo.AddAsync(new ListEntity { Id = listId, Name = "Test", CreatedAt = DateTime.UtcNow });
+
+        var tags = await _tagRepo.GetAllAsync();
+        var agentTag = tags.First(t => t.Name == "agent");
+        await _listRepo.AddTagAsync(listId, agentTag.Id);
+        return (listId, agentTag.Id);
+    }
+
+    private async Task<TaskEntity> SeedQueuedTask(string listId, DateTime? scheduledFor = null, DateTime? createdAt = null)
+    {
+        var task = new TaskEntity
+        {
+            Id = Guid.NewGuid().ToString(),
+            ListId = listId,
+            Title = "Test task",
+            Description = "Do something",
+            Status = TaskStatus.Queued,
+            ScheduledFor = scheduledFor,
+            CreatedAt = createdAt ?? DateTime.UtcNow,
+        };
+        await _taskRepo.AddAsync(task);
+        return task;
+    }
+
+    [Fact]
+    public async Task RunNow_Throws_When_Override_Slot_Busy()
+    {
+        var (listId, _) = await SeedListWithAgentTag();
+        var tcs = new TaskCompletionSource<RunResult>();
+
+        var (service, _) = CreateService((_, _, _, _, _, ct) => tcs.Task);
+
+        var task1 = await SeedQueuedTask(listId);
+        var task2 = await SeedQueuedTask(listId);
+
+        await service.RunNow(task1.Id);
+
+        var ex = await Assert.ThrowsAsync<InvalidOperationException>(() => service.RunNow(task2.Id));
+        Assert.Equal("override slot busy", ex.Message);
+
+        tcs.SetResult(new RunResult { ExitCode = 0, ResultMarkdown = "ok" });
+    }
+
+    [Fact]
+    public async Task RunNow_Throws_For_Unknown_Task()
+    {
+        var (service, _) = CreateService();
+        await Assert.ThrowsAsync<KeyNotFoundException>(() => service.RunNow("nonexistent"));
+    }
+
+    [Fact]
+    public async Task Schedule_Filter_Skips_Future_Tasks()
+    {
+        var (listId, _) = await SeedListWithAgentTag();
+        await SeedQueuedTask(listId, scheduledFor: DateTime.UtcNow.AddHours(1));
+
+        var (service, fake) = CreateService((_, _, _, _, _, _) =>
+            Task.FromResult(new RunResult { ExitCode = 0, ResultMarkdown = "ok" }));
+
+        using var cts = new CancellationTokenSource();
+
+        // Start the service loop, wake it, give it time.
+        await service.StartAsync(cts.Token);
+        service.WakeQueue();
+        await Task.Delay(200);
+        cts.Cancel();
+
+        // The fake should never have been called because the task is scheduled in the future.
+        Assert.Equal(0, fake.CallCount);
+    }
+
+    [Fact]
+    public async Task Queue_FIFO_Sequentiality()
+    {
+        var (listId, _) = await SeedListWithAgentTag();
+
+        var order = new List<string>();
+        var gate1 = new TaskCompletionSource();
+        var gate2 = new TaskCompletionSource();
+        var callCount = 0;
+
+        var (service, _) = CreateService(async (prompt, _, _, taskId, _, ct) =>
+        {
+            var n = Interlocked.Increment(ref callCount);
+            lock (order) { order.Add(taskId); }
+            if (n == 1) await gate1.Task;
+            if (n == 2) gate2.SetResult();
+            return new RunResult { ExitCode = 0, ResultMarkdown = "ok" };
+        });
+
+        var task1 = await SeedQueuedTask(listId, createdAt: DateTime.UtcNow.AddSeconds(-2));
+        var task2 = await SeedQueuedTask(listId, createdAt: DateTime.UtcNow.AddSeconds(-1));
+
+        using var cts = new CancellationTokenSource();
+        await service.StartAsync(cts.Token);
+        service.WakeQueue();
+
+        await Task.Delay(200);
+
+        // Only task1 should be running (task2 waiting).
+        Assert.Single(order);
+        Assert.Equal(task1.Id, order[0]);
+
+        // Release first task.
+        gate1.SetResult();
+
+        // Wait for second task to complete.
+        await gate2.Task.WaitAsync(TimeSpan.FromSeconds(5));
+
+        Assert.Equal(2, order.Count);
+        Assert.Equal(task2.Id, order[1]);
+
+        cts.Cancel();
+    }
+
+    [Fact]
+    public async Task CancelTask_Triggers_Cancellation()
+    {
+        var (listId, _) = await SeedListWithAgentTag();
+
+        var running = new TaskCompletionSource();
+        var cancelled = false;
+
+        var (service, _) = CreateService(async (_, _, _, _, _, ct) =>
+        {
+            running.SetResult();
+            try
+            {
+                await Task.Delay(Timeout.Infinite, ct);
+            }
+            catch (OperationCanceledException)
+            {
+                cancelled = true;
+                throw;
+            }
+            return new RunResult { ExitCode = 0, ResultMarkdown = "ok" };
+        });
+
+        var task = await SeedQueuedTask(listId);
+        await service.RunNow(task.Id);
+
+        await running.Task.WaitAsync(TimeSpan.FromSeconds(5));
+
+        var result = service.CancelTask(task.Id);
+        Assert.True(result);
+
+        await Task.Delay(200);
+        Assert.True(cancelled);
+    }
+
+    [Fact]
+    public async Task GetActive_Returns_Running_Slots()
+    {
+        var (listId, _) = await SeedListWithAgentTag();
+        var tcs = new TaskCompletionSource<RunResult>();
+
+        var (service, _) = CreateService((_, _, _, _, _, _) => tcs.Task);
+
+        var task = await SeedQueuedTask(listId);
+        await service.RunNow(task.Id);
+
+        var active = service.GetActive();
+        Assert.Single(active);
+        Assert.Equal("override", active[0].slot);
+        Assert.Equal(task.Id, active[0].taskId);
+
+        tcs.SetResult(new RunResult { ExitCode = 0, ResultMarkdown = "ok" });
+    }
+}
+
+#region Test doubles
+
+internal sealed class FakeClaudeProcess : IClaudeProcess
+{
+    private readonly Func<string, string, string, string, Func<string, Task>, CancellationToken, Task<RunResult>> _handler;
+    private int _callCount;
+
+    public int CallCount => _callCount;
+
+    public FakeClaudeProcess(
+        Func<string, string, string, string, Func<string, Task>, CancellationToken, Task<RunResult>>? handler = null)
+    {
+        _handler = handler ?? ((_, _, _, _, _, _) =>
+            Task.FromResult(new RunResult { ExitCode = 0, ResultMarkdown = "ok" }));
+    }
+
+    public async Task<RunResult> RunAsync(string prompt, string workingDirectory, string logPath, string taskId,
+        Func<string, Task> onStdoutLine, CancellationToken ct)
+    {
+        Interlocked.Increment(ref _callCount);
+        return await _handler(prompt, workingDirectory, logPath, taskId, onStdoutLine, ct);
+    }
+}
+
+internal sealed class FakeHubContext : IHubContext<WorkerHub>
+{
+    public IHubClients Clients { get; } = new FakeHubClients();
+    public IGroupManager Groups => throw new NotImplementedException();
+}
+
+internal sealed class FakeHubClients : IHubClients
+{
+    private readonly FakeClientProxy _proxy = new();
+    public IClientProxy All => _proxy;
+    public IClientProxy AllExcept(IReadOnlyList<string> excludedConnectionIds) => _proxy;
+    public IClientProxy Client(string connectionId) => _proxy;
+    public IClientProxy Clients(IReadOnlyList<string> connectionIds) => _proxy;
+    public IClientProxy Group(string groupName) => _proxy;
+    public IClientProxy GroupExcept(string groupName, IReadOnlyList<string> excludedConnectionIds) => _proxy;
+    public IClientProxy Groups(IReadOnlyList<string> groupNames) => _proxy;
+    public IClientProxy User(string userId) => _proxy;
+    public IClientProxy Users(IReadOnlyList<string> userIds) => _proxy;
+}
+
+internal sealed class FakeClientProxy : IClientProxy
+{
+    public Task SendCoreAsync(string method, object?[] args, CancellationToken cancellationToken = default) =>
+        Task.CompletedTask;
+}
+
+#endregion