Guardrails so the fd-leak class of bug (Errno 24 lockup; recent SNMP + UniFi
fixes) surfaces early or can't compound, instead of silently killing the app.
- Self-fd watchdog (steward/core/self_monitor.py): records open_fds and
open_fds_pct (% of soft RLIMIT_NOFILE) as "steward"/"process" metrics each
minute through the normal alert pipeline, so the operator can alert on them
via the existing alert-rules UI. Built-in WARNING floor at 80% gives a
zero-config early signal. Stdlib-only (/proc + resource); degrades to a no-op
off Linux. Registered as a core ScheduledTask in app.py.
- Poll-overlap guard (steward/core/scheduler.py): extract a pure _DueTracker
that skips a tick while a task's prior run is still in flight, so a hung poll
can't stack overlapping runs (which amplify per-poll resource/fd use). A
skipped task isn't penalised — it retries the next tick after it completes.
- fd-stability tests (tests/core/): _DueTracker overlap policy, the watchdog
metric/warning/degradation paths, and a real-fd canary that hammers tcp_check
and asserts /proc/self/fd doesn't grow.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
