Autonomous overnight orchestrator — runs the v2 sequence unattended.

Sequence (each step gated on the previous succeeding):

1. Check if USPTO tm_index has >= min_us_rows rows (default 1.5M). If not and force=false, return with 'waiting_on_backfill'.
2. Fire the coexistence matrix ETL via detached subprocess. Returns immediately with the pid + log path.
3. Caller can poll /v1/cron/tm-index-coverage + /v1/cron/verify-diag matrix_stats for completion.

Failure modes handled:

• tm_index missing → returns 'no_tm_index'
• marks table empty → returns 'index_empty'
• ETL script missing → returns 500
• Subprocess fails to spawn → returns 500 with detail

Dual-auth. Idempotent — safe to fire repeatedly.