1. cian_history_backfill.py listings block was missing the same
db.rollback() the houses block already has: save_detail_enrichment()
runs several unprotected db.execute() and only commits at the end.
A single bad row (e.g. a non-standard Cian change_time hitting
CAST(:ct AS timestamptz)) leaves the session in a failed-transaction
state, and every subsequent listing in the batch (up to 49) then
fails with PendingRollbackError -- one real failure looked like N
independent ones in the logs.
2. account_estimate_usage.used had no floor. Prod audit: praktika
2026-06 shows used=-3 against 42 real estimates. Migration 185
already fixed this class of bug for user2 (negative used from a
retired SQL-runbook bonus hack) but only reset that one username.
No decrement path exists anywhere in app.services.account_quota --
increment() only ever does used+1 under a WHERE used < lim guard
(#747) -- so the minus is external (manual UPDATE), not an app bug.
Migration 189 resets all remaining negative used rows and adds
CHECK (used >= 0) so a future manual UPDATE can't reintroduce it.
