buzz-acp accumulates unreaped (defunct) session child processes when agents respawn

# Public issue — buzz-acp leaves claude children unreaped across respawns

> Ready to file at github.com/block/buzz (public, non-security). Attempted via
> API from our side; if permissions refused it, someone with an account posts
> it as-is. Written 2026-08-27 by Otto (codai infrastructure).

**Title:** buzz-acp accumulates unreaped (`defunct`) session child processes when agents respawn

## What we run

A fleet of seven agents on the Buzz relay, each buzz-acp harness running
inside its own container on Debian hosts running Docker. Agents are restarted
regularly by config syncs and deploys — several times a day per agent.

## Observed

Over the last days the host accumulated hundreds of zombie processes —
`claude` child processes in `Z`/`defunct` state whose parent is the still-
running buzz-acp process. A snapshot this morning before cleanup counted
**347** concurrent defunct entries; after a manual restart of the harnesses,
the count returned to baseline (~2).

The pattern tracks respawns: each restart of a session appears to leave one
terminated-but-not-reaped child behind. It is not a memory leak and not a
hang — the zombies sit idle — but it has real costs:

- process monitors and `docker top` output become dominated by defunct
entries until they are indistinguishable from actual workload;
- long-lived hosts drift toward PID-limit pressure;
- incident triage starts from a corrupted picture of what is actually running.

## What we have and haven't verified

- Verified host-side: the counts above and that a clean restart clears them.
- Not reproduced in isolation: a freshly restarted agent container shows zero
zombies immediately, consistent with accumulation only over repeated
respawn cycles on a long-lived parent.

## Ask

Could buzz-acp reap its terminated children — either a `waitpid(..., WNOHANG)`
reaper in its supervise loop or a SIGCHLD handler? Happy to provide full
process trees, kernels, and version detail in this issue if useful.