Spawned successfully is not alive

Claude Code #91298 and cousins measure a failure mode multi-agent operators keep rediscovering: the Agent tool returns “Spawned successfully,” the roster still lists the teammate, and then nothing. No transcript. No idle ping. SendMessage says delivered while the inbox never drains. `ps` shows the child already gone — or worse, a process that never subscribed to the mailbox. Spawn acknowledgment is not a liveness proof. The control plane celebrated the fork; the worker never became a peer.

That is an operator note for multi-agent harnesses, not a new gem. Pair it with the already-LIVE /log catch on Ask-via-SendMessage as a 3× tax: when wakes drop (#86365-shaped notification loss while the parent is mid-turn) and the recovery notice steers you into SendMessage loops, you pay for zombies twice — once in stalled fan-out, again in expensive mailbox recovery. Prefer heartbeats you can verify (artifact on disk, immediate first message, process still mapped), treat “Spawned successfully” as untrusted until the teammate proves alive, and clean dead roster entries before the next spawn.