fix(worker): kill cancelled runs' processes and make MCP approve actually merge

- CancelAsync now signals the running Claude process of the cancelled task and
  its cascaded children via the new RunCancellationRegistry (queue + override
  slots register their CTS there) instead of only flipping DB state.
- external MCP review_task 'approve' now mirrors the hub's ApproveReview:
  unit merge for parents, ApproveAndMergeAsync for childless tasks, optional
  targetBranch; ReviewTaskResult carries mergeStatus/conflicts.

src/ClaudeDo.Worker/External/ExternalMcpService.cs

@@ -6,6 +6,7 @@ using ClaudeDo.Data.Models;
 using ClaudeDo.Data.Repositories;
 using ClaudeDo.Worker.Hub;
 using ClaudeDo.Worker.Lifecycle;
+using ClaudeDo.Worker.Planning;
 using ClaudeDo.Worker.Queue;
 using ClaudeDo.Worker.State;
 using ClaudeDo.Worker.Worktrees;
@@ -18,6 +19,7 @@ namespace ClaudeDo.Worker.External;
 public sealed record TaskListDto(string Id, string Name, string? WorkingDir);
 public sealed record DeleteTaskResult(bool Deleted, string Id);
 public sealed record CancelTaskResult(bool Cancelled, string Id);
+public sealed record ReviewTaskResult(TaskDto Task, string? MergeStatus, IReadOnlyList<string> MergeConflicts, string? MergeMessage);
 public sealed record StatusValueDto(string Status, string Meaning);
 
 public sealed record TaskDto(
@@ -72,6 +74,7 @@ public sealed class ExternalMcpService
     private readonly IDbContextFactory<ClaudeDoDbContext> _dbFactory;
     private readonly WorktreeMaintenanceService _maintenance;
     private readonly TaskMergeService _merge;
+    private readonly PlanningMergeOrchestrator _planningMerge;
 
     public ExternalMcpService(
         TaskRepository tasks,
@@ -82,7 +85,8 @@ public sealed class ExternalMcpService
         GitService git,
         IDbContextFactory<ClaudeDoDbContext> dbFactory,
         WorktreeMaintenanceService maintenance,
-        TaskMergeService merge)
+        TaskMergeService merge,
+        PlanningMergeOrchestrator planningMerge)
     {
         _tasks = tasks;
         _lists = lists;
@@ -93,6 +97,7 @@ public sealed class ExternalMcpService
         _dbFactory = dbFactory;
         _maintenance = maintenance;
         _merge = merge;
+        _planningMerge = planningMerge;
     }
 
     [McpServerTool, Description("List all task lists available in ClaudeDo.")]
@@ -292,34 +297,74 @@ public sealed class ExternalMcpService
 
     [McpServerTool, Description(
         "Review a task that is WaitingForReview. " +
-        "decision='approve' → Done. " +
+        "decision='approve' → review+merge, exactly like the UI's Approve: a childless task merges its worktree into " +
+        "targetBranch (default: the repo's current branch) then goes Done; a task with children drives the unit merge " +
+        "(parent worktree if active + each Done child in order); a task without an active worktree approves straight to Done. " +
+        "mergeStatus 'conflict' means the merge stopped on conflicts (files listed) — resolve them in the ClaudeDo UI. " +
         "decision='reject_rerun' → Queued and re-runs, resuming the agent's session with your feedback as the next turn (feedback is required). " +
         "decision='reject_park' → Idle for manual editing (feedback ignored). " +
         "decision='cancel' → Cancelled. " +
         "Fails if the task is not currently WaitingForReview (except cancel, which also works while Running/Queued).")]
-    public async Task<TaskDto> ReviewTask(
+    public async Task<ReviewTaskResult> ReviewTask(
         string taskId,
         string decision,
         string? feedback = null,
+        string? targetBranch = null,
         CancellationToken cancellationToken = default)
     {
         _ = await _tasks.GetByIdAsync(taskId, cancellationToken)
             ?? throw new InvalidOperationException($"Task {taskId} not found.");
 
-        TransitionResult result = decision.Trim().ToLowerInvariant() switch
+        string? mergeStatus = null;
+        IReadOnlyList<string> mergeConflicts = Array.Empty<string>();
+        string? mergeMessage = null;
+
+        if (decision.Trim().ToLowerInvariant() == "approve")
         {
-            "approve"      => await _state.ApproveReviewAsync(taskId, cancellationToken),
-            "reject_rerun" => await _state.RejectToQueueAsync(taskId, feedback ?? "", cancellationToken),
-            "reject_park"  => await _state.RejectToIdleAsync(taskId, cancellationToken),
-            "cancel"       => await _state.CancelAsync(taskId, DateTime.UtcNow, cancellationToken),
-            _ => throw new InvalidOperationException(
-                $"Unknown decision '{decision}'. Use approve, reject_rerun, reject_park, or cancel."),
-        };
+            // Approve is the single review+merge action — mirror the hub's ApproveReview
+            // routing instead of only flipping the status (which left branches unmerged).
+            bool hasChildren;
+            await using (var ctx = await _dbFactory.CreateDbContextAsync(cancellationToken))
+                hasChildren = await ctx.Tasks.AnyAsync(t => t.ParentTaskId == taskId, cancellationToken);
 
-        if (!result.Ok)
-            throw new InvalidOperationException(result.Reason ?? "Review action failed.");
+            if (hasChildren)
+            {
+                await _planningMerge.StartAsync(taskId, targetBranch ?? "", cancellationToken);
+                var parentDone = (await _tasks.GetByIdAsync(taskId, cancellationToken))!.Status == TaskStatus.Done;
+                mergeStatus = parentDone ? TaskMergeService.StatusMerged : TaskMergeService.StatusConflict;
+                if (!parentDone)
+                    mergeMessage = "unit merge paused on a conflict — resolve and continue it in the ClaudeDo UI";
+            }
+            else
+            {
+                var r = await _merge.ApproveAndMergeAsync(taskId, targetBranch ?? "", cancellationToken);
+                if (r.Status == TaskMergeService.StatusBlocked)
+                    throw new InvalidOperationException(r.ErrorMessage ?? "approve failed");
+                mergeStatus = r.Status;
+                mergeConflicts = r.ConflictFiles;
+                mergeMessage = r.Status == TaskMergeService.StatusConflict
+                    ? "merge conflict — the task stays WaitingForReview; resolve it in the ClaudeDo UI"
+                    : r.ErrorMessage;
+            }
+        }
+        else
+        {
+            TransitionResult result = decision.Trim().ToLowerInvariant() switch
+            {
+                "reject_rerun" => await _state.RejectToQueueAsync(taskId, feedback ?? "", cancellationToken),
+                "reject_park"  => await _state.RejectToIdleAsync(taskId, cancellationToken),
+                "cancel"       => await _state.CancelAsync(taskId, DateTime.UtcNow, cancellationToken),
+                _ => throw new InvalidOperationException(
+                    $"Unknown decision '{decision}'. Use approve, reject_rerun, reject_park, or cancel."),
+            };
 
-        return ToDto((await _tasks.GetByIdAsync(taskId, cancellationToken))!);
+            if (!result.Ok)
+                throw new InvalidOperationException(result.Reason ?? "Review action failed.");
+        }
+
+        return new ReviewTaskResult(
+            ToDto((await _tasks.GetByIdAsync(taskId, cancellationToken))!),
+            mergeStatus, mergeConflicts, mergeMessage);
     }
 
     [McpServerTool, Description("Immediately run a task in the override execution slot (bypasses the agent queue).")]