feat(mission-control): give the list handler its own review task

"Let Claude handle it" now creates one ClaudeDo task per run to host the
ConPTY session (Idle/IsManual, never queued) instead of an untracked
ad-hoc tile, so the run has a real title, diff, and review outcome.
Since the handler merges its own changes straight into the list's
working dir, the task never gets a WorktreeEntity; its review range
lives as new HandlerBaseCommit/HandlerHeadCommit columns on TaskEntity
instead, reusing the existing commit-range diff machinery and keeping
it out of the worktrees overview entirely.

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

@@ -523,23 +523,47 @@ public class MissionControlViewModelTests : IDisposable
             => throw new InvalidOperationException("spec failed");
     }
 
+    private sealed class ThrowingCreateMergeHelperTaskWorker : StubWorkerClient
+    {
+        public override Task<string> CreateMergeHelperTaskAsync(
+            IReadOnlyList<string> taskIds, string listId, string title, string descriptionHeader, CancellationToken ct = default)
+            => throw new InvalidOperationException("create failed");
+    }
+
+    private sealed class FixedTaskIdMergeHelperWorker : StubWorkerClient
+    {
+        public string TaskId { get; } = "fixed-handler-task";
+        public int CreateCallCount { get; private set; }
+        public override Task<string> CreateMergeHelperTaskAsync(
+            IReadOnlyList<string> taskIds, string listId, string title, string descriptionHeader, CancellationToken ct = default)
+        {
+            CreateCallCount++;
+            return Task.FromResult(TaskId);
+        }
+    }
+
     [Fact]
-    public async Task OpenMergeHelperConPtySessionAsync_AddsAdHocPane()
+    public async Task OpenMergeHelperConPtySessionAsync_AddsTaskBasedPane()
     {
         var worker = new FakeWorker();
         using var vm = BuildVm(worker);
 
         await vm.OpenMergeHelperConPtySessionAsync("L1", new[] { "t1", "t2" });
 
-        Assert.Single(vm.ConPtySessions);
-        Assert.Null(vm.ConPtySessions[0].TaskId);
+        var pane = Assert.Single(vm.ConPtySessions);
+        Assert.NotNull(pane.TaskId);
+        Assert.True(pane.IsTaskBased);
         Assert.Single(vm.Panes);
         Assert.Same(vm.ConPtySessions[0], vm.Panes[0]);
     }
 
     [Fact]
-    public async Task OpenMergeHelperConPtySessionAsync_TwoRuns_NeverDeduped()
+    public async Task OpenMergeHelperConPtySessionAsync_TwoRuns_EachGetsItsOwnTaskAndPane()
     {
+        // Each run creates a brand-new handler task (the stub returns a fresh Guid per call),
+        // so two runs still yield two distinct, non-deduped panes -- but for a different reason
+        // than the old ad-hoc pane (never deduped by construction): dedup is now by TaskId, and
+        // there simply is no shared TaskId across separate runs.
         var worker = new FakeWorker();
         using var vm = BuildVm(worker);
 
@@ -547,6 +571,22 @@ public class MissionControlViewModelTests : IDisposable
         await vm.OpenMergeHelperConPtySessionAsync("L1", new[] { "t1" });
 
         Assert.Equal(2, vm.ConPtySessions.Count);
+        Assert.NotEqual(vm.ConPtySessions[0].TaskId, vm.ConPtySessions[1].TaskId);
+    }
+
+    [Fact]
+    public async Task OpenMergeHelperConPtySessionAsync_SameHandlerTaskId_FocusesExistingPane_NoDuplicate()
+    {
+        var worker = new FixedTaskIdMergeHelperWorker();
+        using var vm = BuildVm(worker);
+
+        await vm.OpenMergeHelperConPtySessionAsync("L1", new[] { "t1" });
+        var firstPane = Assert.Single(vm.ConPtySessions);
+
+        await vm.OpenMergeHelperConPtySessionAsync("L1", new[] { "t1" });
+
+        Assert.Single(vm.ConPtySessions);
+        Assert.Same(firstPane, vm.FocusedPane);
     }
 
     [Fact]
@@ -577,6 +617,21 @@ public class MissionControlViewModelTests : IDisposable
         Assert.NotNull(error);
     }
 
+    [Fact]
+    public async Task OpenMergeHelperConPtySessionAsync_TaskCreationThrows_RaisesErrorReported_NoPaneCreated()
+    {
+        var worker = new ThrowingCreateMergeHelperTaskWorker();
+        using var vm = BuildVm(worker);
+        string? error = null;
+        vm.ErrorReported += msg => error = msg;
+
+        await vm.OpenMergeHelperConPtySessionAsync("L1", new[] { "t1" });
+
+        Assert.Empty(vm.ConPtySessions);
+        Assert.Empty(vm.Panes);
+        Assert.NotNull(error);
+    }
+
     [Fact]
     public void ToggleLayoutCommand_FlipsIsFocusMode()
     {