Persistence — Drift / SQLite

The on-device store is the single source of truth: with no server, everything must rebuild from this DB alone after process death, reboot, or restore. Push invariants into the schema, confine Drift to one layer, make every mutation one durable transaction, and store canonical values only. Applies to any lib/data/ Drift table, DAO, repository, connection setup, or backup.

Read the reference for the task at hand:

• references/schema-and-daos.md — audit-column mixin, STRICT/CHECK/FK invariants, canonical column types, the index + EXPLAIN QUERY PLAN gate, DAO↔repository split, files-on-disk-with-relative-paths for blobs.
• references/backup-and-wal.md — the checkpoint→vacuum→verify-by-reopen primitive, WAL rules, the backup-before-anything lesson, optional SQLCipher (key-first, assert-cipher, header-check).
• references/persistence-without-drift.md — the same discipline for a small app on plain JSON files (injected base dir, debounce + lifecycle flush, atomic writes, lenient decode).

Run scripts/check-drift-confinement.sh and scripts/check-persistence-bans.sh before a PR. Migrations and their tests: see run-migration.

Non-negotiable rules