fix(claude-do): merge Status-Force-Bypässe auf laufende Tasks schließen (MCP + UI-

ClaudeDo-Task: 3b2c4015-226b-41a1-80c4-3a8d5537f2a5

src/ClaudeDo.Ui/ViewModels/Islands/TaskRowViewModel.cs

@@ -171,6 +171,13 @@ public sealed partial class TaskRowViewModel : ViewModelBase
         IsRunning ? (true, null) : (false, Loc.T("tasks.reasonNotRunning"));
     public string? CancelDisabledReason => CancelGate().Reason;
 
+    // Gates "Mark Done"/"Mark Cancelled" in the context menu — forcing either status while the
+    // task is actively running would strand the CLI process untracked (WorkerHub.SetTaskStatus
+    // rejects it server-side too; this is the UI-visible half of that guard).
+    private (bool Can, string? Reason) MarkAsGate() =>
+        IsRunning ? (false, Loc.T("tasks.reasonAlreadyRunning")) : (true, null);
+    public string? MarkAsDisabledReason => MarkAsGate().Reason;
+
     // "Open quick session" has no precondition today (see A1's file header) — kept as a
     // placeholder so the menu wiring is uniform; always null until a real gate exists.
     public string? QuickSessionDisabledReason => null;
@@ -318,6 +325,7 @@ public sealed partial class TaskRowViewModel : ViewModelBase
         OnPropertyChanged(nameof(CancelDisabledReason));
         OnPropertyChanged(nameof(RefineDisabledReason));
         OnPropertyChanged(nameof(PlanningDisabledReason));
+        OnPropertyChanged(nameof(MarkAsDisabledReason));
     }
 
     partial void OnParentTaskIdChanged(string? value)

src/ClaudeDo.Ui/Views/Islands/TaskRowView.axaml.cs

@@ -67,8 +67,8 @@ public partial class TaskRowView : UserControl
 
         // "Mark as" — exclusive-choice hiding inside is unchanged; the header is never empty.
         var markAs = new MenuItem { Header = Loc.T("tasks.ctxMarkAs"), DataContext = row };
-        markAs.Items.Add(MakeItem("tasks.ctxMarkDone", OnSetStatusClick, tag: "Done"));
-        markAs.Items.Add(MakeItem("tasks.ctxMarkCancelled", OnSetStatusClick, tag: "Cancelled"));
+        markAs.Items.Add(MakeItem("tasks.ctxMarkDone", OnSetStatusClick, tag: "Done", reason: row.MarkAsDisabledReason));
+        markAs.Items.Add(MakeItem("tasks.ctxMarkCancelled", OnSetStatusClick, tag: "Cancelled", reason: row.MarkAsDisabledReason));
         markAs.Items.Add(new Separator());
         markAs.Items.Add(MakeItem("tasks.ctxMarkManual", OnToggleManualClick, !row.IsManual));
         markAs.Items.Add(MakeItem("tasks.ctxMarkClaudeTask", OnToggleManualClick, row.IsManual));

src/ClaudeDo.Worker/External/ExternalMcpService.cs

@@ -592,8 +592,9 @@ public sealed class ExternalMcpService
         string taskId,
         [Description("'Idle' (reset to editable), 'Queued' (enqueue for execution), 'Cancelled' (retire without " +
                      "deleting; can be reset to Idle later) or 'Done' (mark complete; refused if the task has an " +
-                     "active worktree — use review_task to approve and merge that worktree instead). No other " +
-                     "value is settable externally.")]
+                     "active worktree — use review_task to approve and merge that worktree instead). 'Idle' and " +
+                     "'Done' are both refused while the task is Running — cancel it first. No other value is " +
+                     "settable externally.")]
         string status,
         CancellationToken cancellationToken)
     {
@@ -609,8 +610,9 @@ public sealed class ExternalMcpService
         switch (target)
         {
             case TaskStatus.Idle:
-                await _tasks.ResetToManualAsync(taskId, cancellationToken);
-                await _broadcaster.TaskUpdated(taskId);
+                var idleResult = await _state.ResetToIdleAsync(taskId, cancellationToken);
+                if (!idleResult.Ok)
+                    throw new InvalidOperationException(idleResult.Reason ?? "Cannot reset task to Idle.");
                 break;
 
             case TaskStatus.Queued:
@@ -627,6 +629,9 @@ public sealed class ExternalMcpService
                 break;
 
             case TaskStatus.Done:
+                if (task.Status == TaskStatus.Running)
+                    throw new InvalidOperationException("Cannot mark a running task Done — cancel it first.");
+
                 await using (var ctx = await _dbFactory.CreateDbContextAsync(cancellationToken))
                 {
                     var wt = await new WorktreeRepository(ctx).GetByTaskIdAsync(taskId, cancellationToken);
@@ -886,7 +891,21 @@ public sealed class ExternalMcpService
         if (task.Status == TaskStatus.Running)
             throw new InvalidOperationException("Cannot delete a running task. Cancel it first.");
 
-        await _tasks.DeleteAsync(taskId, cancellationToken);
+        try
+        {
+            await _tasks.DeleteAsync(taskId, cancellationToken);
+        }
+        // TaskRepository.DeleteAsync uses ExecuteDeleteAsync, which bypasses SaveChanges and
+        // surfaces provider errors directly as SqliteException rather than DbUpdateException.
+        catch (Exception ex) when (
+            (ex is Microsoft.Data.Sqlite.SqliteException || ex.InnerException is Microsoft.Data.Sqlite.SqliteException)
+            && (ex.Message.Contains("FOREIGN KEY", StringComparison.OrdinalIgnoreCase)
+                || ex.InnerException?.Message.Contains("FOREIGN KEY", StringComparison.OrdinalIgnoreCase) == true))
+        {
+            throw new InvalidOperationException(
+                "This task has child tasks. Discard the planning session or delete child tasks first.");
+        }
+
         if (task.ParentTaskId is not null)
             await _state.TryAdvanceParentAsync(task.ParentTaskId);
         await _broadcaster.TaskUpdated(taskId);

src/ClaudeDo.Worker/Hub/WorkerHub.cs

@@ -586,6 +586,13 @@ public sealed class WorkerHub : Microsoft.AspNetCore.SignalR.Hub
     {
         if (!Enum.TryParse<TaskStatus>(status, ignoreCase: true, out var parsed))
             throw new HubException($"unknown status: {status}");
+
+        await using var ctx = await _dbFactory.CreateDbContextAsync(Context.ConnectionAborted);
+        var current = await new TaskRepository(ctx).GetByIdAsync(taskId, Context.ConnectionAborted)
+            ?? throw new HubException("task not found");
+        if (current.Status == TaskStatus.Running)
+            throw new HubException("Cannot change the status of a running task. Cancel it first.");
+
         // Queueing goes through the gated transition so draft subtasks can't be queued;
         // other statuses keep the unconditional "set status freely" affordance.
         var result = parsed == TaskStatus.Queued

src/ClaudeDo.Worker/Runner/TaskRunner.cs

@@ -550,7 +550,9 @@ public sealed class TaskRunner
 
         if (isStandalone && pendingChildren.Count > 0)
         {
-            await _state.SubmitForChildrenAsync(task.Id, finishedAt, reviewResult, CancellationToken.None);
+            var transition = await _state.SubmitForChildrenAsync(task.Id, finishedAt, reviewResult, CancellationToken.None);
+            if (!transition.Ok)
+                _logger.LogWarning("SubmitForChildrenAsync rejected for task {TaskId}: {Reason}", task.Id, transition.Reason);
             foreach (var child in pendingChildren)
                 await _state.EnqueueAsync(child.Id, CancellationToken.None);
             await _broadcaster.WorkerLog(
@@ -560,13 +562,17 @@ public sealed class TaskRunner
         }
         else if (isStandalone)
         {
-            await _state.SubmitForReviewAsync(task.Id, finishedAt, reviewResult, CancellationToken.None);
+            var transition = await _state.SubmitForReviewAsync(task.Id, finishedAt, reviewResult, CancellationToken.None);
+            if (!transition.Ok)
+                _logger.LogWarning("SubmitForReviewAsync rejected for task {TaskId}: {Reason}", task.Id, transition.Reason);
             await _broadcaster.WorkerLog($"Finished #{task.Number} \"{task.Title}\" (waiting for review)", WorkerLogLevel.Success, DateTime.UtcNow);
             await _broadcaster.TaskFinished(slot, task.Id, "waiting_for_review", finishedAt);
         }
         else
         {
-            await _state.CompleteAsync(task.Id, finishedAt, reviewResult, CancellationToken.None);
+            var transition = await _state.CompleteAsync(task.Id, finishedAt, reviewResult, CancellationToken.None);
+            if (!transition.Ok)
+                _logger.LogWarning("CompleteAsync rejected for task {TaskId}: {Reason}", task.Id, transition.Reason);
             await _broadcaster.WorkerLog($"Finished #{task.Number} \"{task.Title}\" (done)", WorkerLogLevel.Success, DateTime.UtcNow);
             await _broadcaster.TaskFinished(slot, task.Id, "done", finishedAt);
         }
@@ -583,8 +589,10 @@ public sealed class TaskRunner
         try
         {
             var finishedAt = DateTime.UtcNow;
-            await _state.FailAsync(taskId, finishedAt, error, CancellationToken.None,
+            var transition = await _state.FailAsync(taskId, finishedAt, error, CancellationToken.None,
                 failureReason, turnCount > 0 ? turnCount : null, maxTurns);
+            if (!transition.Ok)
+                _logger.LogWarning("FailAsync rejected for task {TaskId}: {Reason}", taskId, transition.Reason);
             await _broadcaster.WorkerLog($"Finished #{taskNumber} \"{taskTitle}\" (failed)", WorkerLogLevel.Error, DateTime.UtcNow);
             await _broadcaster.TaskFinished(slot, taskId, "failed", finishedAt);
             _logger.LogWarning("Task {TaskId} failed (turns={Turns}): {Error}", taskId, turnCount, error);