510 stories had stale 1_backlog stages in the CRDT because they were
imported during the filesystem→CRDT migration and then moved forward
via filesystem-only moves that never wrote CRDT ops. This made done
stories appear as ghost entries in the backlog.
On startup, reads the authoritative stage from pipeline_items and
corrects any CRDT entries that disagree.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>