Issue 21772 runtime reproduction BEFORE
Commit: 8d3b061121
Environment: fs-34 Linux x64; real web dev server + Claude Agent claude-opus-5-5; browser 1280x800; isolated seeded state.
Steps: parent delegates async Claude child; child native Bash sleep 60 run_in_background=true; returns WAITING; later background notification triggers CANARY final. Parent never polls or sends child messages.

PARENT
{"ordinal": 1, "status": "completed", "requestedAt": "2026-10-22T10:04:52.738Z", "completedAt": "2026-10-22T10:05:13.085Z", "delegatedTaskId": null}
{"ordinal": 2, "status": "completed", "requestedAt": "2026-10-22T10:06:16.378Z", "completedAt": "2026-10-22T10:06:22.000Z", "delegatedTaskId": null}
assistant: DELEGATED-21772 (task identifier omitted)
completion notification: WAITING-21772
assistant: The child task reported WAITING-21772, and the system marked it completed after that first turn. I'm ending my turn here without polling, and I'll reply if the CANARY-21772-FINAL notification comes in.

CHILD
{"ordinal": 1, "status": "completed", "requestedAt": "2026-10-22T10:05:02.871Z", "completedAt": "2026-10-22T10:05:17.417Z", "delegatedTaskId": null}
{"ordinal": 2, "status": "completed", "requestedAt": "2026-10-22T10:06:16.496Z", "completedAt": "2026-10-22T10:06:18.398Z", "delegatedTaskId": null}
assistant: WAITING-21772
notification: {"source": {"kind": "background_command"}, "outcome": "completed", "summary": "Command \"Sleep for 60 seconds\" finished"}
assistant: CANARY-21772-FINAL

Observed: child final run completed with CANARY-21772-FINAL; parent received only WAITING-21772 and had no final notification or third run.