fix(worker): stateless AbortPlanningMerge after worker restart mid-merge

PlanningMergeOrchestrator._states is in-memory. A worker restart during a
conflict pause left the list repo mid-merge with no recovery path: both
ContinuePlanningMerge and AbortPlanningMerge threw "no in-progress merge",
and re-Approving failed on the IsMidMergeAsync guard.

AbortAsync now falls through to a stateless path when no _states entry exists:
it looks up the parent's list WorkingDir and, if the repo is mid-merge, runs
git merge --abort there directly, then broadcasts PlanningMergeAborted.
Parent remains WaitingForReview — the next Approve restarts the unit merge
(already-Merged child worktrees are skipped as before).

ContinueAsync error message now points to AbortPlanningMerge as the recovery
action. StartAsync mid-merge guard also carries an actionable hint.

Tests: AbortAsync stateless + mid-merge (restart recovery), AbortAsync
stateless + clean repo (clear error).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/ClaudeDo.Worker.Tests/Planning/PlanningMergeOrchestratorTests.cs

@@ -245,6 +245,59 @@ public sealed class PlanningMergeOrchestratorTests : IDisposable
         Assert.False(await git.IsMidMergeAsync(repo.RepoDir, CancellationToken.None));
     }
 
+    // ─── Stateless abort (post-restart recovery) ───────────────────────────
+
+    /// <summary>
+    /// Worker restarted while a conflict was paused: _states is empty but the list repo is
+    /// still mid-merge. AbortAsync must abort the dangling merge, broadcast PlanningMergeAborted,
+    /// and leave the parent in WaitingForReview so a fresh Approve can retry.
+    /// </summary>
+    [Fact]
+    public async Task AbortAsync_NoState_RepoMidMerge_AbortsAndBroadcasts()
+    {
+        var db = NewDb();
+        var repo = NewRepo();
+        GitRepoFixture.RunGit(repo.RepoDir, "branch", "-m", "main");
+
+        var (parentId, _, subB, _) = await SeedPlanningThreeChildrenMiddleConflictsAsync(db, repo);
+
+        // Drive orch1 into the conflict pause — repo is now mid-merge.
+        var (orch1, _) = BuildOrchestrator(db);
+        await orch1.StartAsync(parentId, "main", CancellationToken.None);
+
+        // Simulate restart: fresh orchestrator has no in-memory state.
+        var (orch2, spy) = BuildOrchestrator(db);
+
+        await orch2.AbortAsync(parentId, CancellationToken.None);
+
+        var git = new GitService();
+        Assert.False(await git.IsMidMergeAsync(repo.RepoDir, CancellationToken.None));
+
+        using var ctx = db.CreateContext();
+        Assert.Equal(TaskStatus.WaitingForReview, ctx.Tasks.Single(t => t.Id == parentId).Status);
+
+        Assert.Contains(spy, c => c.Method == "PlanningMergeAborted" && (string)c.Args[0]! == parentId);
+    }
+
+    /// <summary>
+    /// No in-memory state and repo is clean — nothing to abort. Must throw a clear error.
+    /// </summary>
+    [Fact]
+    public async Task AbortAsync_NoState_RepoNotMidMerge_ThrowsClear()
+    {
+        var db = NewDb();
+        var repo = NewRepo();
+        GitRepoFixture.RunGit(repo.RepoDir, "branch", "-m", "main");
+
+        var (parentId, _, _) = await SeedPlanningWithTwoNonConflictingChildrenAsync(db, repo);
+
+        var (orch, _) = BuildOrchestrator(db);
+
+        var ex = await Assert.ThrowsAsync<InvalidOperationException>(
+            () => orch.AbortAsync(parentId, CancellationToken.None));
+        Assert.Contains("no in-progress merge", ex.Message);
+    }
+
     private (PlanningMergeOrchestrator orch, List<(string Method, object?[] Args)> calls) BuildOrchestrator(DbFixture db)
     {
         var fakeHub = new OrchestratorFakeHubContext();