refactor(worker): drop ForceSetStatusAsync, route every status write through a guarded transition

Mark-done now fires OnChildTerminalAsync, so ticking a chain child or the last open child
off by hand unblocks the successor and advances the parent. The hub's Mark-as menu and
update_task_status map onto MarkDone/Cancel(retire)/Enqueue/Reset; revert_merge uses the
new ReopenForReviewAsync (Done|WaitingForReview -> WaitingForReview).

tests/ClaudeDo.Worker.Tests/State/TaskStateServiceTests.cs

@@ -534,6 +534,58 @@ public sealed class TaskStateServiceTests : IDisposable
         Assert.Equal(TaskStatus.Done, await GetStatusAsync(id));
     }
 
+    [Fact]
+    public async Task MarkDoneAsync_OnChainChild_UnblocksSuccessor()
+    {
+        var parent = await SeedTaskAsync(TaskStatus.WaitingForChildren, phase: PlanningPhase.Finalized);
+        var c0 = await SeedTaskAsync(TaskStatus.Queued, parentId: parent, sortOrder: 0);
+        var c1 = await SeedTaskAsync(TaskStatus.Queued, parentId: parent, sortOrder: 1, blockedBy: c0);
+
+        await _sut.MarkDoneAsync(c0, DateTime.UtcNow, default);
+
+        Assert.Null((await GetTaskAsync(c1)).BlockedByTaskId);
+    }
+
+    [Fact]
+    public async Task MarkDoneAsync_OnLastOpenChild_AdvancesParentToReview()
+    {
+        var parent = await SeedTaskAsync(TaskStatus.WaitingForChildren, phase: PlanningPhase.Finalized);
+        await SeedTaskAsync(TaskStatus.Done, parentId: parent);
+        var open = await SeedTaskAsync(TaskStatus.Failed, parentId: parent);
+
+        await _sut.MarkDoneAsync(open, DateTime.UtcNow, default);
+
+        Assert.Equal(TaskStatus.WaitingForReview, await GetStatusAsync(parent));
+    }
+
+    [Theory]
+    [InlineData(TaskStatus.Done, true)]
+    [InlineData(TaskStatus.WaitingForReview, true)]
+    [InlineData(TaskStatus.Idle, false)]
+    [InlineData(TaskStatus.Running, false)]
+    public async Task ReopenForReviewAsync_OnlyFromDoneOrReview(TaskStatus from, bool ok)
+    {
+        var id = await SeedTaskAsync(from);
+
+        var result = await _sut.ReopenForReviewAsync(id, default);
+
+        Assert.Equal(ok, result.Ok);
+        Assert.Equal(ok ? TaskStatus.WaitingForReview : from, await GetStatusAsync(id));
+    }
+
+    [Theory]
+    [InlineData(TaskStatus.Idle)]
+    [InlineData(TaskStatus.Failed)]
+    public async Task CancelAsync_Retire_AllowsIdleAndFailed(TaskStatus from)
+    {
+        var id = await SeedTaskAsync(from);
+
+        var result = await _sut.CancelAsync(id, DateTime.UtcNow, default, retire: true);
+
+        Assert.True(result.Ok);
+        Assert.Equal(TaskStatus.Cancelled, await GetStatusAsync(id));
+    }
+
     [Fact]
     public async Task UnmarkDoneAsync_FromDone_TransitionsToIdle()
     {