feat(worker): surface rebase and worktree-maintenance progress on OperationProgress

RebaseOthersAfterMergeAsync now broadcasts a "rebasing" phase with i/n over the
WaitingForReview branches it checks, so the merge/continue_merge callers stop
showing the stalled "Merging…" phase while the best-effort rebase loop runs
(rebase still runs before the verify gate; a failed rebase still leaves the
merge itself successful). WorktreeMaintenanceService gained an optional
HubBroadcaster to report the same i/n shape per worktree during
cleanup/reset, with no new UI surface (deliberately out of scope). Both
review-action viewmodels now also listen on OperationProgressEvent (which
carries the total that the elapsed-seconds-only MergeProgressEvent drops) to
render "Rebasing other worktrees… (i/n)".

tests/ClaudeDo.Ui.Tests/ViewModels/DetailsIslandReviewActionsTests.cs

@@ -255,6 +255,40 @@ public class DetailsIslandReviewActionsTests : IDisposable
         Assert.Equal(0, MergeProgressSubscriberCount(worker));
     }
 
+    private static int OperationProgressSubscriberCount(StubWorkerClient worker)
+    {
+        var field = typeof(StubWorkerClient).GetField("OperationProgressEvent",
+            System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);
+        var del = (Delegate?)field!.GetValue(worker);
+        return del?.GetInvocationList().Length ?? 0;
+    }
+
+    [Fact]
+    public async Task ApproveReview_ShowsRebasePhase_WithBranchCount_InsteadOfStalledMerging()
+    {
+        var worker = new BlockingApproveWorkerClient();
+        var vm = BuildVm(worker);
+        vm.Bind(new TaskRowViewModel { Id = "task-approve-rebase", Status = TaskStatus.WaitingForReview });
+        vm.Monitor.ApplyState(TaskStatus.WaitingForReview);
+
+        var approve = vm.ApproveReviewCommand.ExecuteAsync(null);
+        var merging = vm.ApproveOp.Label;
+
+        // The rebase phase needs the branch total, which only rides OperationProgress
+        // (MergeProgressEvent forwards elapsed-seconds only) — ignored for other tasks.
+        worker.RaiseOperationProgress("some-other-task", "rebasing", 1, 3);
+        Assert.Equal(merging, vm.ApproveOp.Label);
+
+        worker.RaiseOperationProgress("task-approve-rebase", "rebasing", 2, 3);
+        Assert.NotEqual(merging, vm.ApproveOp.Label);
+        Assert.Contains("(2/3)", vm.ApproveOp.Label);
+
+        worker.Gate.SetResult(new MergeResultDto("merged", new List<string>(), null));
+        await approve;
+
+        Assert.Equal(0, OperationProgressSubscriberCount(worker));
+    }
+
     private sealed class BlockingSubmitWorkerClient : StubWorkerClient
     {
         public override bool IsConnected => true;

tests/ClaudeDo.Ui.Tests/ViewModels/MergeModalViewModelTests.cs

@@ -119,4 +119,26 @@ public class MergeModalViewModelTests
 
         Assert.Null(vm.ProgressMessage);
     }
+
+    [Fact]
+    public async Task Submit_shows_the_rebase_phase_with_branch_count_instead_of_stalled_merging()
+    {
+        var (vm, worker) = Build();
+        await vm.InitializeAsync("task-1", "do the thing");
+        worker.BlockMerge = true;
+
+        var submit = vm.SubmitCommand.ExecuteAsync(null);
+        var merging = vm.ProgressMessage;
+
+        // Needs the branch total, which only rides OperationProgress (MergeProgressEvent
+        // forwards elapsed-seconds only) -- and must not be clobbered by that other forwarder.
+        worker.RaiseOperationProgress("task-1", "rebasing", 1, 2);
+        Assert.NotEqual(merging, vm.ProgressMessage);
+        Assert.Contains("(1/2)", vm.ProgressMessage);
+
+        worker.MergeGate.SetResult(new MergeResultDto("merged", new List<string>(), null));
+        await submit;
+
+        Assert.Null(vm.ProgressMessage);
+    }
 }