Maintainer rework of #45580 (issue #54036) on top of the contributor's
cherry-pick, which targeted spectrum-ts 3.1.0 while main pins 8.0.0:
Sidecar (primary detection, new):
- stream-staleness.mjs: pure decision rules, executable under node.
* classifyProbeRejection: only a not-found-shaped rejection of the
synthetic-id read counts as a completed round-trip (ALIVE); any other
rejection is INCONCLUSIVE — never alive. The original /probe treated
ANY rejection as alive, which was too loose.
* shouldProbe: probe only after 10+ min of stream silence (configurable
via PHOTON_STREAM_SILENCE_PROBE_MS; <=0 disables) with a cooldown.
* isZombieSuspect: zombie only on silence past threshold AND a
probe-proven live channel. Silence alone NEVER degrades (shared lines
can be quiet for hours); inconclusive probes NEVER degrade (network
may be down — the iterator will throw and the re-subscribe loop
recovers on its own).
- index.mjs: track last inbound-iterator yield (noteInboundYield), run a
30s watchdog tick, and on a confirmed zombie feed markStreamDegraded ->
the existing exit-75 restart path. /healthz gains a stream.staleness
block (silentForMs, threshold, lastProbeOutcome, zombieSuspected).
/probe reworked to strict semantics: 200 only on a proven round-trip,
503 with outcome hung|inconclusive otherwise.
Adapter (second layer, reworked):
- _probe_once returns tri-state alive|hung|inconclusive; only a hung
sidecar HTTP call counts toward the respawn counter — inconclusive
resets nothing and triggers nothing.
- default probe_interval_seconds 60 -> 600 (conservative; avoid restart
storms on quiet lines).
- _monitor_sidecar_health surfaces zombieSuspected from /healthz as a
warning; the fatal UPSTREAM_STREAM_DEGRADED path is unchanged and fires
when the sidecar escalates.
Tests: test_zombie_stream_watchdog.py executes the real node decision
module and drives the adapter against mocked /healthz responses;
test_presence_watchdog.py updated for the tri-state probe.
Also adds contributor mappings for nickkarhan (#53283) and vaibhavjnf
(#45580).
