diff --git a/assets/oh-my-opencode.schema.json b/assets/oh-my-opencode.schema.json
index b215a7c8..308b177c 100644
--- a/assets/oh-my-opencode.schema.json
+++ b/assets/oh-my-opencode.schema.json
@@ -77,6 +77,7 @@
           "claude-code-hooks",
           "auto-slash-command",
           "edit-error-recovery",
+          "sisyphus-task-retry",
           "prometheus-md-only",
           "start-work",
           "sisyphus-orchestrator"
diff --git a/src/features/background-agent/manager.ts b/src/features/background-agent/manager.ts
index f166b476..40870190 100644
--- a/src/features/background-agent/manager.ts
+++ b/src/features/background-agent/manager.ts
@@ -262,7 +262,11 @@ export class BackgroundManager {
   }): Promise<BackgroundTask> {
     const existingTask = this.tasks.get(input.taskId)
     if (existingTask) {
-      if (input.parentSessionID !== existingTask.parentSessionID) {
+      // P2 fix: Clean up old parent's pending set BEFORE changing parent
+      // Otherwise cleanupPendingByParent would use the new parent ID
+      const parentChanged = input.parentSessionID !== existingTask.parentSessionID
+      if (parentChanged) {
+        this.cleanupPendingByParent(existingTask)  // Clean from OLD parent
         existingTask.parentSessionID = input.parentSessionID
       }
       if (input.parentAgent !== undefined) {
@@ -281,8 +285,8 @@ export class BackgroundManager {
         const pending = this.pendingByParent.get(input.parentSessionID) ?? new Set()
         pending.add(existingTask.id)
         this.pendingByParent.set(input.parentSessionID, pending)
-      } else {
-        // Don't re-add completed/cancelled tasks; clean any stale entry
+      } else if (!parentChanged) {
+        // Only clean up if parent didn't change (already cleaned above if it did)
         this.cleanupPendingByParent(existingTask)
       }