Fold the whole raw-retention window of already-recorded KpiSample rows into
KpiRollupHourly once shortly after the recorder singleton starts, so long-range
(30 d/90 d) trend charts aren't blank until enough wall-clock passes after
deploy. Reuses Task 3's idempotent FoldHourlyRollupsAsync over
[TruncateToHour(now) - RetentionDays, TruncateToHour(now)); runs at most once
per actor lifetime (_backfillDone latch) and defers past / blocks the periodic
lookback fold via a dedicated _backfillInFlight guard so the two idempotent
upserts never race on overlapping rows. Best-effort: no exception escapes; logs
start, window, and elapsed on completion. No Host or options change.
Claude-Session: https://claude.ai/code/session_01MtdgwpEeCUn6cUA5f1LMPj
Joseph Doherty
bedf3c55f0