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.Data/Repositories/TaskRepository.cs

@@ -258,9 +258,15 @@ public sealed class TaskRepository
         string? commitType,
         CancellationToken ct = default)
     {
-        var parent = await _context.Tasks.FirstOrDefaultAsync(t => t.Id == parentId, ct);
+        // AsNoTracking: SetPlanningStartedAsync mutates via ExecuteUpdate which
+        // bypasses the change tracker; a tracked Find would return stale data.
+        var parent = await _context.Tasks.AsNoTracking()
+            .FirstOrDefaultAsync(t => t.Id == parentId, ct);
         if (parent is null)
             throw new InvalidOperationException($"Parent task {parentId} not found.");
+        if (parent.PlanningPhase == PlanningPhase.None)
+            throw new InvalidOperationException(
+                $"Parent task {parentId} is not in a planning phase; cannot attach children.");
 
         var maxSort = await _context.Tasks
             .Where(t => t.ListId == parent.ListId)
@@ -401,8 +407,9 @@ public sealed class TaskRepository
             .FirstOrDefaultAsync(t => t.PlanningSessionToken == token, ct);
     }
 
-    public async Task<bool> DiscardPlanningAsync(
+    public async Task<DiscardPlanningOutcome> DiscardPlanningAsync(
         string parentId,
+        bool dequeueQueuedChildren,
         CancellationToken ct = default)
     {
         using var tx = await _context.Database.BeginTransactionAsync(ct);
@@ -413,10 +420,54 @@ public sealed class TaskRepository
         if (parent is null || parent.PlanningPhase != PlanningPhase.Active)
         {
             await tx.RollbackAsync(ct);
-            return false;
+            return new DiscardPlanningOutcome(DiscardPlanningResult.NotInPlanning, 0, 0);
         }
 
-        // Children created during the planning session are Status=Idle, PlanningPhase=None.
+        var children = await _context.Tasks
+            .Where(t => t.ParentTaskId == parentId)
+            .Select(t => new { t.Id, t.Status })
+            .ToListAsync(ct);
+
+        var runningCount = children.Count(c => c.Status == TaskStatus.Running);
+        if (runningCount > 0)
+        {
+            await tx.RollbackAsync(ct);
+            return new DiscardPlanningOutcome(DiscardPlanningResult.BlockedByRunningChildren, 0, runningCount);
+        }
+
+        var queuedIds = children.Where(c => c.Status == TaskStatus.Queued).Select(c => c.Id).ToList();
+        if (queuedIds.Count > 0)
+        {
+            if (!dequeueQueuedChildren)
+            {
+                await tx.RollbackAsync(ct);
+                return new DiscardPlanningOutcome(DiscardPlanningResult.BlockedByQueuedChildren, queuedIds.Count, 0);
+            }
+
+            await _context.Tasks
+                .Where(t => queuedIds.Contains(t.Id))
+                .ExecuteUpdateAsync(s => s
+                    .SetProperty(t => t.Status, TaskStatus.Idle)
+                    .SetProperty(t => t.BlockedByTaskId, (string?)null), ct);
+        }
+
+        // Terminal children (Done/Failed/Cancelled) survive the discard but cannot remain
+        // attached: their parent's PlanningPhase is about to be reset to None, which would
+        // make them orphans. Promote them to top-level.
+        var terminalIds = children
+            .Where(c => c.Status == TaskStatus.Done
+                     || c.Status == TaskStatus.Failed
+                     || c.Status == TaskStatus.Cancelled)
+            .Select(c => c.Id)
+            .ToList();
+        if (terminalIds.Count > 0)
+        {
+            await _context.Tasks
+                .Where(t => terminalIds.Contains(t.Id))
+                .ExecuteUpdateAsync(s => s.SetProperty(t => t.ParentTaskId, (string?)null), ct);
+        }
+
+        // Idle children created during this planning session are dropped.
         await _context.Tasks
             .Where(t => t.ParentTaskId == parentId
                         && t.Status == TaskStatus.Idle
@@ -433,7 +484,27 @@ public sealed class TaskRepository
                 .SetProperty(t => t.PlanningFinalizedAt, (DateTime?)null), ct);
 
         await tx.CommitAsync(ct);
-        return true;
+        return new DiscardPlanningOutcome(DiscardPlanningResult.Discarded, queuedIds.Count, 0);
+    }
+
+    /// <summary>
+    /// Clears <c>ParentTaskId</c> on rows whose parent is missing or no longer in a
+    /// planning phase. Returns the number of rows repaired. Idempotent.
+    /// </summary>
+    internal async Task<int> RepairOrphanedChildrenAsync(CancellationToken ct = default)
+    {
+        var orphanIds = await _context.Tasks
+            .Where(t => t.ParentTaskId != null)
+            .Where(t => !_context.Tasks.Any(p =>
+                p.Id == t.ParentTaskId && p.PlanningPhase != PlanningPhase.None))
+            .Select(t => t.Id)
+            .ToListAsync(ct);
+
+        if (orphanIds.Count == 0) return 0;
+
+        return await _context.Tasks
+            .Where(t => orphanIds.Contains(t.Id))
+            .ExecuteUpdateAsync(s => s.SetProperty(t => t.ParentTaskId, (string?)null), ct);
     }
 
     public async Task TryCompleteParentAsync(