Red commit: 97c9a22a55 (CI:
https://github.com/Kpa-clawbot/CoreScope/commit/97c9a22a55b07d1576c579aa9d23b290dad33eb6/checks)
Fixes#1285.
## What was broken
**Bug A — outlier-dominated hash-evidence median.** On the per-hash
evidence panel a single observer reporting an RTC-reset advert (firmware
emitting factory timestamp, ~700d off) dragged the displayed median to
"median corrected: -704d 18h" even when every other observer of that
hash saw a normal value.
**Bug B — false "N of last K had nonsense timestamps" warning.**
`recentBadSampleCount` lumped RTC-reset adverts in with "bimodal-bad"
samples. On the repro node every recent skew was -16…-22s (healthy), but
the lone RTC-reset advert that landed inside the recent window was
counted as bad → "3 of last 5 adverts had nonsense timestamps" fired and
the node was misclassified `bimodal_clock`.
Root cause of B: the recent-window split (`cmd/server/clock_skew.go`
~L575) classified anything `|corrected skew| > 1h` as "bad". That
conflates true bimodal RTC oscillation (1h…24h) with factory-timestamp
resets (>24h, already surfaced via the RTC-reset badge).
## Fix
- New `rtcResetOutlierThresholdSec = 24h`. Rationale: real µC drift is
sub-second/advert; real bimodal RTC misbehaves in the hours range;
anything >1d is not a drift signal.
- Recent-window split puts `|skew| > 24h` in a third bucket excluded
from both `recentSampleCount` and `recentBadCount`.
- New `hashEvidenceMedian()` filters outliers before computing the
per-hash median. UI labels the hash "insufficient data (N RTC-reset
outliers excluded)" when every observer saw a reset-shaped advert.
- Three pre-existing #845 tests used -50M-sec "bad" samples (RTC-reset
range) — re-pointed to -7200s (true bimodal range), what `bimodal_clock`
actually models.
## Preflight overrides
- check-branch-clean: cross-stack: justified — backend computes
counts/median; frontend renders the new label.
## Browser verification
Confirmed staging node `c0dedad…` repro matches the test fixture. No new
CSS vars.
## E2E assertion added
`cmd/server/clock_skew_issue1285_test.go:81` and `:103`.
---------
Co-authored-by: corescope-bot <bot@corescope.local>
Kpa-clawbot
467b01a1b3