The objective_corpus_room_month index migration (#1942) was committed to
backend/data/sql/171_*, but the main deploy runner applies migrations from
repo-root data/sql/*.sql (deploy.yml:280) and the path trigger is data/sql/**.
So the file never ran — prod still seq-scans (verified post-deploy: index
absent, query 265ms). Move it to data/sql/171_* (alongside 170) so it deploys.
No SQL change; the index itself was dry-run-verified on prod (BEGIN/ROLLBACK).
Light1YT
23cc188972