# @deepseek-ai/dsh-session-persistence-sqlite

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A SQLite durable session-persistence backend — a second `SessionPersistence` implementation ([session persistence](../../../.agents/notes/implemented/architecture/2026-06-14-session-persistence.md)), built to validate that the abstract seam and the shared `runPersistenceContract` suite are genuinely backend-agnostic. It satisfies the SAME contract as `dsh-session-persistence-jsonl` (append-only, contiguous-seq, lazy materialization, interrupted-turn close on load), expressed over `node:sqlite` rows instead of file bytes.

`locate(meta)` returns `undefined`: all sessions share one database, so there is no honest independent per-session transcript path.

> **TODO:** this backend talks to `node:sqlite` directly. If a cordis database service (`cordis/db` / a `@cordisjs` SQL driver plugin) is adopted, route through that instead of holding a raw `DatabaseSync` here — the contract surface (`SessionPersistence`) would not change, only the storage driver.

## Storage model

Each `SessionEvent` maps 1:1 onto a row in an `events` table `(session_id, seq, type, time, data, source_event_seqs, surface_op)` — `data` is the event payload as JSON text, so the row shape is the event verbatim (including `assistant/chunk`, keeping `seq` contiguous). The two `TEXT` columns `source_event_seqs` and `surface_op` are nullable; they store the event's optional surface-metadata fields (see [session surface](../../../.agents/notes/implemented/architecture/2026-06-18-session-surface.md)). Out-of-log metadata (`SessionHeader`), a per-materialization incarnation id, and a monotonic per-log revision live in a `sessions` row; `createdAt` is a non-negative safe integer stored in a strict `INTEGER` column. A singleton state row carries the immutable store id. A `sessions` row is written only by the first `append` — its existence is the lazy-materialization signal (`list` reports exactly the sessions that have a row).

The repository's Node range supports unflagged `node:sqlite`. The database enables foreign keys and uses the configured journal mode (`wal` by default; use a rollback mode where WAL shared-memory files are unsuitable). `PRAGMA application_id` identifies the canonical persistence database, and `PRAGMA user_version` stores its layout version. A fresh database must have no application identity or user-defined schema objects; initialization creates every table and stamps both pragmas in one transaction. Non-pristine unversioned databases, foreign application identities, and every non-current version reject before journal-mode mutation because this unreleased format has no migrations.

On filesystems with POSIX modes, the backend requests mode `0700` for missing directories and exclusively creates a missing database with mode `0600` before SQLite opens it; the process umask may further restrict both. New WAL, shared-memory, and persistent rollback-journal sidecars receive the database's resulting owner-only mode. Existing directories, database files, and sidecars keep their modes; filesystem setup errors other than an existing database fail initialization. These defaults prevent incidental exposure through a permissive process umask, but do not protect database confidentiality or integrity when another principal can replace the database entry in its parent directory.

## Contract semantics over rows

- **Append = a transaction.** `append` runs `BEGIN`/`COMMIT` around the batch: it materializes the `sessions` row (if still lazy) and INSERTs every event, asserting the contiguous-seq contract first (the first event's `seq` must equal the stored next-seq). A mid-batch failure (a UNIQUE violation on a duplicated seq) rolls back entirely, so the stored log and the in-memory cursor stay consistent. (`load()` already balanced the stored log, so `append` never has to repair a crash tail.)
- **Lazy materialization.** `create()` records intent in memory only — no row is written until the first `append`. A created-but-never-appended session has no `sessions` row, so it is absent from `list()` (which reports exactly the sessions that have a row).
- **Interrupted-turn close on load.** `load()` implements the shared [crash-recovery contract](../../../.agents/notes/implemented/architecture/2026-06-14-session-persistence.md): preserve the valid interrupted turn, append its synthetic closing events in one transaction, and remove only a torn tail row. Committed parse errors or sequence gaps make the session unloadable. Because recovery mutates stored rows, the next append starts from a balanced log and accurate cursor.
- **Non-mutating inspection.** `inspect()` returns an immutable balanced logical view and may synthesize recovery closers in memory, without deleting a torn tail row, appending recovery rows, or changing the lightweight revision.
- **Lightweight revisions.** `listSnapshots(signal?)` combines the immutable store and database-file identity, a per-materialization incarnation id, and a per-session counter incremented in each mutating transaction. A full-prefix read captures that revision and its event rows in one read transaction, while `readStoredRevision()` queries only the session row to validate retained preparations. This keeps unchanged observations stable without parsing event rows and distinguishes independent stores and recreated same-id logs. It checks cancellation before and after shared readiness and the synchronous metadata query; the query itself is non-preemptible.

## Configuration (schemastery)

```ts
interface Config {
  path: string   // SQLite database file path, or ':memory:' for an in-process DB
  journalMode?: 'wal' | 'delete' | 'truncate' | 'persist'   // journal_mode pragma; default 'wal'
  preparedSessionCacheSize?: number   // positive integer; default 5
}
```

## Write path

Like the JSONL backend, the plugin copies each frozen `session/event` into one controller per live session and starts an eager drain. Concurrent events share the current transaction; events admitted during it form a follow-up batch, while `session/flush` waits until both current and pending batches are durable. The controller persists a fork's seed once, keeps a write cursor so resume never re-appends stored events, and seeds live sessions on apply because HMR does not replay `session/created`. Dispose drains every retained controller before closing the database.

## Model Experience

### Resumed conversation history

#### What the model sees

SQLite storage contributes no live prompt or schema. Loading restores the same surface history as JSONL and preserves prior headers for reconstruction; the new loop composes its current envelope. Recovery balances an assistant request without a durable call with `TOOL_NOT_STARTED`; a durable call without a result becomes `TOOL_OUTCOME_UNKNOWN`, which tells the model to retry only read-only or idempotent work and to verify possible side effects or ask the user. Row metadata and raw chunks are not messages.

#### Token effect

Zero live-request tokens. Resume restores retained history and pays the current envelope, plus the quoted repair result for each interrupted call.

#### KV Cache effect

SQLite storage does not mutate live request prefixes. A resumed loop can reuse provider cache only when its reconstructed history, current envelope, and model route match; crash-repair results append.

## Known Limitations and Deferred Work

- **`DatabaseSync` is synchronous** — every append transaction blocks the event loop for its duration; acceptable for local stores, a throughput ceiling for busy multi-session servers.
- **Write contention has no wait or retry policy** — the backend sets no busy timeout and retries no locked-database error, so another connection holding a write transaction makes the operation reject immediately.
- **Only a pristine new database or the current owned `SCHEMA_VERSION` opens** — unversioned schema objects, foreign application identities, and every other schema version are rejected rather than migrated (unreleased software; no persisted user data to preserve).
- **Nothing deletes stored sessions** — rows accumulate until removed externally (the seam has no deletion surface; `ON DELETE CASCADE` is wired for such out-of-band cleanup).
