0144 — The claim reads the pre-update `claimed` via an `old_values` CTE, not PostgreSQL 18's `old` alias

Context. ClaimMessagesWithCursor must return the window (low, high], which requires seeing the cursor’s claimed value from before the UPDATE in the same statement. PostgreSQL 18 adds built-in old/new transition aliases in RETURNING, but depending on them pins the minimum server version.

Decision. Capture the pre-update value in a CTE named old_values, joined back via FROM so RETURNING old_values.claimed AS low, cursor.claimed AS high can see it. The name deliberately avoids old so PG18’s built-in alias cannot shadow it.

Consequences. The query works on PostgreSQL versions below 18 and does not silently change meaning on 18+. Rejected: the PG18 old transition alias — an 18-only feature, and reusing the bare name old for the CTE would be shadowed by the built-in.