fix(delegate-task): cancel child background tasks on parent abort and timeout in unstable agent flow

src/tools/delegate-task/cancel-unstable-agent-task.ts

@@ -0,0 +1,19 @@
+import type { ExecutorContext } from "./executor-types"
+
+export async function cancelUnstableAgentTask(
+  manager: ExecutorContext["manager"],
+  taskID: string | undefined,
+  reason: string
+): Promise<void> {
+  if (!taskID || typeof manager.cancelTask !== "function") {
+    return
+  }
+
+  await Promise.allSettled([
+    manager.cancelTask(taskID, {
+      source: "unstable-agent-task",
+      reason,
+      skipNotification: true,
+    }),
+  ])
+}