[maxmad64bis]

Stacked on #15888. Only the last commit is this PR's; I'll rebase once it lands.

⚠️ base-red inherited: #15306

Summary

Stall log lines showed inflight=0 with no warning when the sampler returned an unusable reading, hiding it among real zeros. When the sampler returns NaN or a negative value, the fallback keeps zero but stays silent, while a throwing sampler warns once. Now an unusable reading falls back to zero with the same one-time warning, so a zero from a broken sampler is marked as such.

Related Issues

• No linked issue — found while reading the event loop stall recorder

Target Branch

• Base is the active release/v3.8.x branch (the highest open release/v*), not main
• New feature? From 3.8.55 on it is held with the v4-feature label for the v4 channel

Validation

• Change type: other
• Focused tests and category gates from the golden path
• npm run lint
• Reconciled with the current active release base; focused checks rerun afterward
• Production-code changes include a new or updated automated test in this PR

Tests Added Or Updated

• tests/unit/event-loop-stall.test.ts — new cases for NaN, negative and unbounded sampler readings (each falls back to zero with a single warning) and a healthy reading (count kept, no warning).

Coverage Notes

• src/lib/healthzLag.ts — covered by tests/unit/event-loop-stall.test.ts.

Reviewer Notes

• Behavior: stall lines that fall back to inflight=0 from an unusable sampler reading now carry the existing one-time warning; healthy readings are unchanged.
• Merge: lands on fix(monitoring): log event-loop stalls with counter on health #15888; either order with perf(cache): serve the usage-history part of the cache page from the shared response cache #16361 and fix(sse): cover opencode-zen with the egress-IP lockout and feed body-text rules #16797 — this warning rewrites the fallback its recorder added, so it cannot land first.

[diegosouzapw]

Hi @maxmad64bis — closing this pull request to clear the open queue. The branch fix/event-loop-stall-sampler-nan-warn is kept, so the commits stay. Comment here if it should be reopened.

[diegosouzapw]

Hi @maxmad64bis — reopening this pull request. The close was a mistake, and it is back in the merge queue. The branch fix/event-loop-stall-sampler-nan-warn was kept.