par2 file lists dropped once their holders are final; late candidates claimable

Most par2 sets describe readable uploads whose files are never hashed, so they
were never complete and kept forever (19 GB). Candidates added to a release
after it settled were never marked ready (93,642 since 2026-10-13); the batch
store and merge mark them now, migration 5100 repairs the waiting ones
(LOG.md 2026-10-20 (87)).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

REBUILD.md

@@ -242,6 +242,10 @@ It reads what's new an hour (`created_at`) at a time, its place kept after
 each, and merges only the sets held or matched by two releases or more; a
 file whose first 16 KiB and size more than 20 files share is a common one and
 matches nothing (LOG.md 2026-10-20 (85)).
+A set's file list is dropped once it can't merge anything more: complete (all
+its files in its holder), judged (every holder junk), or final (every holder
+inside a run of done ranges, those ranges' candidates probed, its hashes seen
+by the merger); `par2_sets` stays (LOG.md 2026-10-20 (87)).
 
 **Backlog: voyager 1's features not in voyager 2** (CONCEPT.md decisions;
 voyager 1's data exported to `/mnt/bulk/usenet-rebuild/v1-export/` on