On a pinned tier (the hub holds a CONFIRMED append-only key) the only
legitimate fall of the box's snapshot count is a clean-up window the hub
opened. The checker now compares prev - cur with what the windows closed
since the previous trustworthy report removed (store.RemovedByWindowsBetween,
2 h slack for the in-run count lag); any unexplained fall, even one snapshot,
raises offsite_snapshots_dropped (error) saying 'outside any clean-up window
the hub opened'. A window that cannot say what it removed (timeout, still
open) explains anything: no alarm, one INFO line. Non-pinned tiers keep the
half-rule. Untrustworthy reports: unchanged (no alarm, baseline kept).
Red tests: r435_pinned_drop_test.go (3 fail with the pinned rule disabled;
WindowExplainsFall fails when windows are ignored), r435_windows_between_test.go.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS
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