# SPEC-009 — Persistence

One SQLite database per deployment (`<history-directory>/bot.db`),
replacing the per-channel pickle files (`<channel>.dat`,
`<channel>.memory`). Stdlib `sqlite3` via worker threads — no new
dependency (D-010). Without `history-directory` in config the bot
runs memory-only, as before.

### PER-01 — History survives restarts (coverage: test)

History entries written through the store are returned, in order and
per channel, by a fresh store instance on the same database file.

### PER-02 — Memory survives restarts (coverage: test)

The per-channel memory string written through the store is returned
by a fresh store instance on the same database file.

### PER-03 — Existing pickles migrate exactly once (coverage: test)

On responder start, when the database holds no rows for the channel
and legacy pickle files exist, their content is imported and the
pickle files are renamed to `*.migrated` (kept for rollback). A
second start does not re-import. Users keep their history through
the cutover (review consensus: migration is a decision, not an
accident).

### PER-04 — Database hygiene (coverage: test)

The database runs in WAL journal mode, carries `PRAGMA user_version`
= schema version (currently 1) for future migrations/rollback
policy, and the file is chmod 0600 (it stores conversation data).

### PER-05 — Writes run off the event loop (coverage: test)

History and memory persistence happen in a worker thread
(`asyncio.to_thread`) — a slow disk cannot stall Discord event
handling (D6).