Three related ADR-104 follow-ups:
1. Expose per-node drift_score on PerNodeFeatureInfo (skip-if-none
so legacy v1 baseline.json — no per_subcarrier_mean — emits
nothing instead of misleading 0.0).
2. raw.html drift sparkline below the RSSI/broadband trace, fixed
Y range [0, 0.30] with dashed presence (0.10) + warning (0.15)
thresholds so operators can read off-axis presence across nodes
without re-scaling. Stat pill "drift" shows the live numeric.
3. baseline_staleness_watch background task: when the on-disk
baseline is older than --baseline-stale-age-sec (default 4 h)
AND drift > 1.5× presence threshold for ≥3 consecutive 5-min
ticks while the classifier reports `absent`, logs a warning
suggesting recalibration. Rate-limited via
--baseline-stale-warn-cooldown-sec (default 1 h). Independent
from auto-recalibrate: that one needs a quiet room; this one
fires when the operator is *in* the room while the channel
itself has physically shifted (AP moved, furniture, etc.).
Co-Authored-By: claude-flow <ruv@ruv.net>
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