fix(mcp): merge_task marks the task Done after a successful merge

merge_task only flipped the worktree to Merged; it never transitioned the task
status. With allowWaitingForReview this left a merged task stuck in
WaitingForReview. Approve it to Done on a successful merge (a Done task is
already terminal). Mirrors the ApproveAndMergeAsync review flow.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/ClaudeDo.Worker/External/ExternalMcpService.cs

@@ -468,6 +468,12 @@ public sealed class ExternalMcpService
 
         if (result.Status == TaskMergeService.StatusMerged)
         {
+            // MergeAsync only flips the worktree to Merged; a merged task must also
+            // reach Done. If it was still awaiting review, approve it now (a Done task
+            // is already terminal and needs no transition).
+            if (task.Status == TaskStatus.WaitingForReview)
+                await _state.ApproveReviewAsync(taskId, cancellationToken);
+
             string? mergeCommit = null;
             try
             {

tests/ClaudeDo.Worker.Tests/External/ExternalMcpServiceTests.cs

@@ -708,6 +708,27 @@ public sealed class ExternalMcpServiceTests : IDisposable
         Assert.Null(result.MergeCommit);
     }
 
+    [Fact]
+    public async Task MergeTask_WaitingForReview_WithFlag_MarksTaskDone()
+    {
+        if (!GitAvailable) { Assert.True(true, "git not available -- skipping"); return; }
+
+        var (task, list, wt) = await SeedWorktreeAsync(TaskStatus.WaitingForReview);
+        File.WriteAllText(Path.Combine(wt.WorktreePath, "added.txt"), "content");
+        var cfg = new WorkerConfig { WorktreeRootStrategy = "sibling" };
+        var mgr = new WorktreeManager(new GitService(), _db.CreateFactory(), cfg, NullLogger<WorktreeManager>.Instance);
+        await mgr.CommitIfChangedAsync(wt, task, list, CancellationToken.None);
+
+        var target = await new GitService().GetCurrentBranchAsync(list.WorkingDir, CancellationToken.None);
+        var sut = BuildSut(CreateQueue());
+
+        var result = await sut.MergeTask(task.Id, target, true, dryRun: false, allowWaitingForReview: true, CancellationToken.None);
+
+        Assert.True(result.Merged);
+        var reloaded = await new TaskRepository(_db.CreateContext()).GetByIdAsync(task.Id);
+        Assert.Equal(TaskStatus.Done, reloaded!.Status);
+    }
+
     // ── ContinueTask validation ───────────────────────────────────────────────
 
     [Fact]