v0.88.2

Changed

• The fine tier is kept for two hours, and the readers stop reaching into it past the last hour. It has exactly two consumers: RECENT_BUCKETS' twelve buckets, which are the last-hour rate, and roll_up_hours(), which builds every coarse tier out of a closed hour's fine buckets. It is the window's EDGE and the fold's input — never a tier to read old hours from — and both of those need two hours, not four: the plan's fine span is just under two at the worst minute, and an hour folds within a re-probe of it closing. FINE_TTL_SECONDS 14400 → 7200, which costs 24 buckets a shard against the coarse tier's 24 hours; the four hours it was, and the "288 buckets a shard" the old note costed it at, bought margin for a fallback that should not have been reading here at all.
• unfolded_hour_buckets() now reaches only the GRACE hour — the one immediately behind the fine tail, which the fold may simply not have caught yet — and filters even that to the buckets the TTL can still hold. Everything older is the coarse tier's alone, folded or not: roll_up_hours() reads the same keys, so an hour it never reached is gone from here for it too. Cold batch counts per poll, four partitions, against the 0.88.1 numbers: overview 28 → 20, urls 448 → 320, urls --search 896 → 640, urls --include_workers 896 → 640 — 5.4x off where this release series started, and the same factor off the worst-case mirror walks behind them.