deepseek-harness/packages/session-persistence/session-persistence-sqlite/src/schema.ts

/**
 * Schema + load-time helpers for the SQLite session-persistence backend: the
 * DDL (a `sessions` metadata table and a 1:1 `events` row per `SessionEvent`),
 * the database open/configure step, and the last-`turn/end` cut that gives the
 * SQLite backend the SAME crash-tail-on-load semantics as the JSONL backend.
 *
 * @module dsh-session-persistence-sqlite/schema
 */

import { DatabaseSync } from 'node:sqlite'
import type { SessionEvent, SessionId, SessionHeader, SurfaceOp } from '@deepseek-ai/dsh-session'

/**
 * The on-disk schema version. Bumped only on a breaking change to the table
 * layout; orthogonal to a session's own `version` (which versions the EVENT
 * vocabulary, stored per session in the `sessions` row).
 */
export const SCHEMA_VERSION = 5

/**
 * A row of the `sessions` table — the out-of-log metadata ({@link SessionHeader}).
 * The row's EXISTENCE is the materialization signal: it is written only by the
 * first `append` (lazy materialization), so a created-but-never-appended
 * session has no row and is absent from `list`, mirroring the JSONL
 * backend's "no file until first append".
 */
export interface SessionRow {
  id: string
  version: number
  created_at: number
  cwd: string | null
  parent_session: string | null
  seed_length: number | null
  delegation_depth: number | null
}

/** An `events` table row: one `SessionEvent` mapped 1:1 (`data` is JSON text). */
export interface EventRow {
  seq: number
  type: string
  time: number
  data: string
  /** JSON-encoded `number[]` — the event's sourceEventSeqs, or null. */
  source_event_seqs: string | null
  /** JSON-encoded `SurfaceOp` — how the event entered the surface, or null. */
  surface_op: string | null
}

/**
 * Journal modes the backend will run under. `wal` is the default and the
 * durability model the persistence ADR records; the rollback-journal modes
 * (`delete`/`truncate`/`persist`) exist for filesystems where WAL's
 * shared-memory files do not work (network mounts). `memory`/`off` are
 * excluded: dropping journal durability silently contradicts what this
 * backend promises.
 */
export type JournalMode = 'wal' | 'delete' | 'truncate' | 'persist'

/**
 * Open the database and apply its schema and pragmas. A zero `user_version` is
 * stamped with {@link SCHEMA_VERSION}; every other non-current version rejects
 * rather than being migrated in place.
 * @param path - the SQLite database file to open (created when absent).
 * @param journalMode - validated journal pragma.
 * @returns the open handle with pragmas applied and both tables ensured.
 */
export function openDatabase(path: string, journalMode: JournalMode): DatabaseSync {
  const db = new DatabaseSync(path)
  db.exec('PRAGMA foreign_keys = ON')
  // The validated union is safe to interpolate into a non-bindable PRAGMA.
  db.exec(`PRAGMA journal_mode = ${journalMode.toUpperCase()}`)
  // `PRAGMA user_version` always returns exactly one row { user_version }.
  const { user_version: onDisk } = db.prepare('PRAGMA user_version').get() as { user_version: number }
  if (onDisk !== 0 && onDisk !== SCHEMA_VERSION) {
    db.close()
    throw new Error(`session database at "${path}" has schema version ${onDisk}, incompatible with this build (${SCHEMA_VERSION})`)
  }
  if (onDisk === 0) {
    // Stamp fresh or pre-versioning databases.
    db.exec(`PRAGMA user_version = ${SCHEMA_VERSION}`)
  }
  db.exec(`
    CREATE TABLE IF NOT EXISTS sessions (
      id             TEXT PRIMARY KEY,
      version        INTEGER NOT NULL,
      created_at     INTEGER NOT NULL,
      cwd              TEXT,
      parent_session   TEXT,
      seed_length      INTEGER,
      delegation_depth INTEGER
    ) STRICT
  `)
  db.exec(`
    CREATE TABLE IF NOT EXISTS events (
      session_id        TEXT NOT NULL REFERENCES sessions(id) ON DELETE CASCADE,
      seq               INTEGER NOT NULL,
      type              TEXT NOT NULL,
      time              INTEGER NOT NULL,
      data              TEXT NOT NULL,
      source_event_seqs TEXT,
      surface_op        TEXT,
      PRIMARY KEY (session_id, seq)
    ) STRICT
  `)
  return db
}

/**
 * Reconstruct the {@link SessionHeader} from a `sessions` row.
 * @param row - the `sessions` table row.
 * @returns the header, `NULL` columns mapped to omitted optional fields.
 */
export function rowToMeta(row: SessionRow): SessionHeader {
  return {
    version: row.version,
    id: row.id as SessionId,
    createdAt: row.created_at,
    ...row.cwd !== null ? { cwd: row.cwd } : {},
    ...row.parent_session !== null ? { parentSession: row.parent_session as SessionId } : {},
    ...row.seed_length !== null ? { seedLength: row.seed_length } : {},
    ...row.delegation_depth !== null ? { delegationDepth: row.delegation_depth } : {},
  }
}

/**
 * Reconstruct a {@link SessionEvent} from an `events` row (parses `data`).
 * @param row - the `events` table row; `data` and the surface columns hold JSON text.
 * @returns the reconstructed event; throws when a JSON column fails to parse
 *   ({@link scanRows} treats that as a hole, not corruption, in the tail).
 */
export function rowToEvent(row: EventRow): SessionEvent {
  // Surface-metadata fields are conditional on the event type in the type
  // system; spread them so each variant gets only the fields it declares.
  const surfaceFields = {
    ...row.source_event_seqs !== null ? { sourceEventSeqs: JSON.parse(row.source_event_seqs) as number[] } : {},
    ...row.surface_op !== null ? { surfaceOp: JSON.parse(row.surface_op) as SurfaceOp } : {},
  }
  return {
    type: row.type as SessionEvent['type'],
    seq: row.seq,
    time: row.time,
    data: JSON.parse(row.data) as SessionEvent['data'],
    ...surfaceFields,
  } as SessionEvent
}

/**
 * Find the preserved prefix of ordered event rows. Fully written rows in an
 * interrupted final turn remain in the prefix. The first unparsable row or seq
 * gap after the last `turn/end` marks a tolerated torn tail; the same hole in
 * the committed region rejects.
 *
 * @param rows - one session's event rows, ordered by seq ascending.
 * @returns the preserved event prefix, plus `tornFrom` — the seq the physical
 *   delete starts at — when a torn tail exists.
 */
export function scanRows(rows: readonly EventRow[]): { preserved: SessionEvent[]; tornFrom?: number } {
  // Pass 1: parse each row's data; a row whose data is not valid JSON is a hole.
  // (The seq/type COLUMNS are always present even when `data` is corrupt.)
  interface Parsed { ok: boolean; event?: SessionEvent }
  const parsed: Parsed[] = rows.map((row) => {
    try {
      return { ok: true, event: rowToEvent(row) }
    } catch {
      return { ok: false }
    }
  })

  // The last index that is a valid `turn/end` — holes through a closed turn
  // are always committed corruption.
  let lastTurnEnd = -1
  for (let i = parsed.length - 1; i >= 0; i--) {
    if (parsed[i]?.ok && rows[i]?.type === 'turn/end') { lastTurnEnd = i; break }
  }

  // Preserve the contiguous prefix, including a complete interrupted turn;
  // holes through the last committed boundary throw, while later holes stop.
  const preserved: SessionEvent[] = []
  for (let i = 0; i < rows.length; i++) {
    const p = parsed[i]
    if (!p?.ok || p.event === undefined) {
      if (i <= lastTurnEnd) throw new Error(`corrupt session log: unparsable committed event at seq ${rows[i]?.seq}`)
      break // torn tail fragment after the last turn/end — stop, tolerate
    }
    if (p.event.seq !== i) {
      if (i <= lastTurnEnd) throw new Error(`corrupt session log: seq gap in committed region (expected ${i}, got ${p.event.seq})`)
      break // gap after the last turn/end — torn tail, stop
    }
    preserved.push(p.event)
  }

  // Any rows past the preserved prefix are a never-committed torn tail; their
  // first seq is the deletion point for load's physical repair.
  return preserved.length < rows.length ? { preserved, tornFrom: preserved.length } : { preserved }
}