Crossposts, reposts and backfill ranges keep bringing articles of files
that worker:file already created. Ingest inserted their header parts again,
and GC's copied-parts pass (which searched all binaries for parts on every
batch) removed only 150k-450k per sweep: parts grew to 68M rows, 56M of
them belonging to finished files, and the 23 GB table paused the backfill.
- Ingest skips header parts (no per-part CRC) for binaries with a file_id.
- GC drops copied parts with a cursor over binaries, 2000 per statement.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>