feat(planning): prevent orphaned subtasks via guards + startup repair

Three coordinated guards close the orphan-creation paths:

- CreateChildAsync refuses when the parent is not in a planning phase.
- DiscardPlanningAsync now returns a structured DiscardPlanningOutcome
  and refuses when children are queued or running; callers can opt into
  auto-dequeuing queued kids via dequeueQueuedChildren=true. Terminal
  children (Done/Failed/Cancelled) are promoted to top-level instead of
  becoming orphans when the parent's PlanningPhase is reset.
- OrphanRecovery hosted service clears ParentTaskId on any rows whose
  parent is missing or no longer in a planning phase on worker startup,
  mirroring the StaleTaskRecovery pattern.

UI surfaces the block reason: a confirm dialog offers to dequeue queued
children and retry; a running-children block is shown as a hard error
asking the user to cancel first.

WorkerClient now negotiates the JsonStringEnumConverter so the
DiscardPlanningResult enum round-trips correctly over SignalR.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/ClaudeDo.Ui/Services/WorkerClient.cs

@@ -1,9 +1,11 @@
 using System.Collections.ObjectModel;
 using Avalonia.Threading;
 using ClaudeDo.Data.Models;
+using ClaudeDo.Data.Repositories;
 using CommunityToolkit.Mvvm.ComponentModel;
 using Microsoft.AspNetCore.SignalR;
 using Microsoft.AspNetCore.SignalR.Client;
+using Microsoft.Extensions.DependencyInjection;
 
 namespace ClaudeDo.Ui.Services;
 
@@ -64,6 +66,10 @@ public partial class WorkerClient : ObservableObject, IAsyncDisposable, IWorkerC
         _hub = new HubConnectionBuilder()
             .WithUrl(signalRUrl)
             .WithAutomaticReconnect(new IndefiniteRetryPolicy())
+            .AddJsonProtocol(options =>
+            {
+                options.PayloadSerializerOptions.Converters.Add(new System.Text.Json.Serialization.JsonStringEnumConverter());
+            })
             .Build();
 
         _hub.Reconnected += async _ =>
@@ -436,8 +442,8 @@ public partial class WorkerClient : ObservableObject, IAsyncDisposable, IWorkerC
     public async Task OpenInteractiveTerminalAsync(string taskId, CancellationToken ct = default)
         => await _hub.InvokeAsync("OpenInteractiveTerminalAsync", taskId, ct);
 
-    public async Task DiscardPlanningSessionAsync(string taskId, CancellationToken ct = default)
-        => await _hub.InvokeAsync("DiscardPlanningSessionAsync", taskId, ct);
+    public async Task<DiscardPlanningOutcome> DiscardPlanningSessionAsync(string taskId, bool dequeueQueuedChildren = false, CancellationToken ct = default)
+        => await _hub.InvokeAsync<DiscardPlanningOutcome>("DiscardPlanningSessionAsync", taskId, dequeueQueuedChildren, ct);
 
     public async Task<int> FinalizePlanningSessionAsync(string taskId, bool queueAgentTasks = true, CancellationToken ct = default)
         => await _hub.InvokeAsync<int>("FinalizePlanningSessionAsync", taskId, queueAgentTasks, ct);
@@ -496,8 +502,8 @@ public partial class WorkerClient : ObservableObject, IAsyncDisposable, IWorkerC
         => await StartPlanningSessionAsync(taskId, ct);
     async Task IWorkerClient.ResumePlanningSessionAsync(string taskId, CancellationToken ct)
         => await ResumePlanningSessionAsync(taskId, ct);
-    async Task IWorkerClient.DiscardPlanningSessionAsync(string taskId, CancellationToken ct)
-        => await DiscardPlanningSessionAsync(taskId, ct);
+    async Task<DiscardPlanningOutcome> IWorkerClient.DiscardPlanningSessionAsync(string taskId, bool dequeueQueuedChildren, CancellationToken ct)
+        => await DiscardPlanningSessionAsync(taskId, dequeueQueuedChildren, ct);
     async Task IWorkerClient.FinalizePlanningSessionAsync(string taskId, bool queueAgentTasks, CancellationToken ct)
         => await FinalizePlanningSessionAsync(taskId, queueAgentTasks, ct);
     async Task<int> IWorkerClient.GetPendingDraftCountAsync(string taskId, CancellationToken ct)