v0.88.1

Fixed

• The readers asked for four times more fine buckets than the fine tier keeps. An hour the coarse tier cannot answer for is answered from its twelve fine buckets — the fallback that makes a fresh deploy and a cold-start backfill self-healing — but buckets_in_hour() enumerates all twelve whatever their age, and the plan's hours reach back a whole retention window. urls and urlnames are ROLE_URL_FINE, kept for ttl_url_fine(), four hours. Everything behind that was a key memcache had already discarded: a certain miss, per shard, per chunk, per partition — and each miss is what walked the durable mirror's index in full. FINE_TTL_SECONDS's own docblock asserted "nothing reads a fine bucket behind that", and three readers did.
  Stats_Store::unfolded_hour_buckets() is now the one spelling of that fallback, and it stops at the tier's TTL: the reader's horizon is the writer's. Cold batch counts per poll, four partitions: overview 108 → 28, urls 1,728 → 448, urls --search 3,456 → 896, urls --include_workers 3,456 → 896 — the same factor off the memcache round trips and off the worst-case index walks behind them. Nothing recoverable is lost: roll_up_hours() folds an hour from those same keys, so an hour past the horizon is gone from the fine tier for the fold as well as for the reader.