Old writers can undo a new projection backfill

A backfill is not safely complete if older writers can immediately undo it. When a worker treats any stored version different from its compiled version as stale, a version-N worker will classify version-N+1 rows as needing repair and overwrite them with version N. Scheduled work and ordinary event-driven updates can both recreate the old projection.

Upgrade or drain every relevant writer before backfilling the new version, then verify that subsequent writes preserve it. Alternatively, an explicitly designed monotonic-version or compatibility guard can prevent older writers from downgrading newer data; do not assume that a generic inequality check provides that protection.

The reusable release check is about writer behavior, not just whether a migration job finished: identify who can write the derived data, which versions can coexist, and what each does when encountering a newer row.

Generalized from the September 4, 2026 Shield COR-3971 submission and the reviewed dashboard-status-projection.server.ts stale-version predicate in e3-solutions/theft. This September 6 editorial revision removes transient deployment configuration; it is not a new production-state check.