deepseek-harness/packages/session-persistence-sqlite/README.md

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

A SQLite durable session-persistence backend — a second SessionPersistence implementation (session persistence), 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.

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) — data is the event payload as JSON text, so the row shape is the event verbatim (including assistant/chunk, keeping seq contiguous). Out-of-log metadata (SessionHeader) lives in a sessions row. A sessions row is written only by the first append — its existence is the lazy-materialization signal (has/list report exactly the sessions that have a row), so no separate column is needed.

The repo targets Node ≥ 24 (the root engines field), which includes the stable node:sqlite module. The database opens with foreign_keys = ON (so ON DELETE CASCADE drops a session's events with its row) and journal_mode = WAL. The table-layout version is stored in PRAGMA user_version and checked on open: a fresh database is stamped with the current SCHEMA_VERSION; a database written by any other, incompatible build (a non-current user_version, older or newer) is rejected rather than opened against an unknown layout — there is no migration (unreleased software).

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 has()/list() (which report exactly the sessions that have a row).
• Interrupted-turn close on load. load() reads every stored event ordered by seq and finds the longest seq-contiguous, parseable prefix — INCLUDING the real events of an interrupted final turn after the last turn/end (the loop only flushes at turn/end, so a process killed mid-turn leaves real, fully-written rows past it). A single turn can be huge in a long-horizon task, so those events are preserved, never truncated: load() CLOSES the orphaned turn by durably appending the minimal synthetic boundary events (an error tool/result for every assistant tool call left unanswered, a step/end if a step was open, then a turn/end carrying { kind: 'interrupted' }), inside one transaction that also DELETEs any never-fully-written torn tail row. load() is therefore mutating — after it the stored rows are balanced and the cursor is truthful, so the next append continues cleanly. The boundary (last turn/end, torn-tail detection) is computed from the seq/type columns so a malformed data in a torn tail row is never parsed (discarded, not unloadable). A parse error or seq gap inside the committed region (at or before the last real turn/end) makes the session unloadable. A session whose only turn never closed keeps its metadata row and stays present in has()/list() — the same as the JSONL backend, whose file likewise survives a first append that never reached turn/end.

Configuration (schemastery)

interface Config {
  path: string   // SQLite database file path, or ':memory:' for an in-process DB
}

Write path

Like the JSONL backend, the plugin also installs the session/event → buffer → session/flush drain: it snapshots each event when buffered (the live session.events object is mutable), persists a fork's seed once on session/created, keeps a per-session write cursor so a resumed session never re-appends stored events, and seeds existing live sessions on apply (HMR does not replay session/created). Dispose awaits every in-flight init + final drain and then closes the database, so no write lands after teardown.