pm health hangs with zero output in <= 2026.8.7; a silent hang gives agents no signal to act on #949

Summary

pm health hangs forever, producing zero output, in 2026.8.7 and earlier. It is fixed in 2026.8.8. Filing it anyway because the failure mode — not the specific bug — is what cost us the time, and that failure mode is still reachable by anything that pins an older version.

Reproduction

Same directory, same tracker, only the version differs:

$ cd <any repo with a .agents/pm tracker>

$ timeout 90 npx -y @unbrained/pm-cli@2026.8.7 health; echo "exit=$?"
exit=124        # killed by timeout, no output at all

$ timeout 90 npx -y @unbrained/pm-cli@2026.8.8 health; echo "exit=$?"
exit=0

$ timeout 90 npx -y @unbrained/pm-cli@2026.8.9 health; echo "exit=$?"
exit=0

Reproduced on 6 different repositories with pinned versions 2026.8.3, 2026.8.6 and 2026.8.7 — all hang. The process sits in ep_poll at ~0% CPU with an empty stdout, so the event loop never settles.

Why it is worth a note even though it is fixed

An autonomous agent hit this in our fleet and stalled for ~9 minutes with no signal at all. From the outside, a hang with zero bytes written is indistinguishable from slow work, so the supervising process cannot tell "still going" from "will never finish". A wrong version pin turned into lost wall-clock time rather than an error.

Two things would have made this self-diagnosing regardless of the underlying bug:

1. Emit something before the first blocking step. Even pm health: scanning <root> on stderr converts a silent hang into a locatable one.
2. A default watchdog. If a command has produced no output for N seconds, print what it is waiting on, or fail with a non-zero exit. A gate that can hang indefinitely is a gate that can hang CI indefinitely — and pm health is exactly the command repos wire into release checks.

Both are cheap and would apply to every command, not just this one.

Related

Repos pinning <= 2026.8.7 should be bumped; that is on our side, not yours. Also filed #948, which is the other half of why version skew bit us in the same session.

Environment

• Node 26.5.0, Linux
• @unbrained/pm-cli 2026.8.3 / 2026.8.6 / 2026.8.7 hang; 2026.8.8 / 2026.8.9 exit 0