feat(mcp): add SuggestImprovement tool (server-stamped, one layer deep)

src/ClaudeDo.Worker/Runner/TaskRunMcpService.cs

@@ -0,0 +1,47 @@
+using System.ComponentModel;
+using ClaudeDo.Data.Repositories;
+using ClaudeDo.Worker.Hub;
+using ModelContextProtocol.Server;
+
+namespace ClaudeDo.Worker.Runner;
+
+public sealed record SuggestedImprovementDto(string ChildTaskId);
+
+[McpServerToolType]
+public sealed class TaskRunMcpService
+{
+    private readonly TaskRepository _tasks;
+    private readonly TaskRunMcpContextAccessor _ctx;
+    private readonly HubBroadcaster _broadcaster;
+
+    public TaskRunMcpService(TaskRepository tasks, TaskRunMcpContextAccessor ctx, HubBroadcaster broadcaster)
+    {
+        _tasks = tasks;
+        _ctx = ctx;
+        _broadcaster = broadcaster;
+    }
+
+    [McpServerTool, Description(
+        "File an out-of-scope improvement as a child task of the current task. The child runs " +
+        "automatically after this task finishes and is surfaced for review alongside it. Use ONLY " +
+        "for work that is genuinely outside this task's scope (a refactor, follow-up, or tech debt) " +
+        "— never for work that belongs to the current task.")]
+    public async Task<SuggestedImprovementDto> SuggestImprovement(
+        string title,
+        string description,
+        CancellationToken cancellationToken)
+    {
+        var callerId = _ctx.Current.CallerTaskId;
+        var caller = await _tasks.GetByIdAsync(callerId, cancellationToken)
+            ?? throw new InvalidOperationException("Calling task not found.");
+        if (caller.ParentTaskId is not null)
+            throw new InvalidOperationException(
+                "A child task cannot suggest further improvements (improvements are one layer deep).");
+
+        var child = await _tasks.CreateChildAsync(
+            callerId, title, description, commitType: null, createdBy: callerId, cancellationToken);
+        await _broadcaster.TaskUpdated(child.Id);
+        await _broadcaster.TaskUpdated(callerId);
+        return new SuggestedImprovementDto(child.Id);
+    }
+}