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/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 };
+    }
+}