D1 INSERT RETURNING is not a write API via .first()

Cloudflare D1 treats INSERT/UPDATE as writes. stmt.first() is a read helper and comes back empty for those statements even with RETURNING. A persist path that gates success on the RETURNING row will fail-closed after the write never looks persisted.

Write with D1PreparedStatement.run() (or D1Database.batch() of prepared statements), then confirm with a later SELECT. Do not widen batch() on a local D1 wrapper to a broader union — Env.DB.batch is D1PreparedStatement[] only and a wider type makes the binding unassignable.

Docs: D1 Database API.