ai-persistence-build-custom-adapter

# Custom Chat Persistence The deliverable is **one file in the app** — `src/lib/chat-persistence.ts` — exporting a `ChatPersistence` built from the database client the app already has. Plus whatever DDL that database needs, added through the app's existing migration flow. Do not create a package, a second client, or a migration runner. **Route first.** If the app already runs one of these, stop and use that skill — it has the driver-specific code: | App runs | Use | | ------------------------- | --------------------------------------- | | Drizzle ORM (any dialect) | ai-persistence/build-drizzle-adapter | | Prisma | ai-persistence/build-prisma-adapter | | Cloudflare Workers + D1 | ai-persistence/build-cloudflare-adapter | Everything else lands here. The full contracts and their invariants are in **ai-persistence/stores** and `docs/persistence/store-reference.md`; the complete worked `node:sqlite` walkthrough is `docs/persistence/build-your-own-chat-adapter.md` and `examples/ts-react-chat/src/lib/sqlite-persistence.ts`. ## 1. Read the app before writing anything | Find | Where to look | What it decides | | ------------------ | ------------------------------------------------------------- | ------------------------------------------------------ | | The client | `src/db.ts`, `src/lib/db.ts`, `src/server/db.ts` | What the file imports — never construct a second pool | | Client lifetime | module singleton vs per-request factory (`getDb()`, bindings) | `export const chatPersistence` vs `export function` | | Migration flow | `migrations/`, `drizzle/`, `supabase/migrations/`, an ORM CLI | How the DDL gets applied — use theirs, add nothing new | | Naming conventions | existing tables/collections | Prefix (`chat_*`) so nothing collides | | JSON support | `jsonb` (Postgres), `json` (MySQL 5.7+), text (SQLite) | Whether mappers stringify/parse | | Import alias | `tsconfig.json` `paths` | `@/db`, `~/db`, `#/db`, or a relative path | ## 2. Shape the storage Four logical records. Whatever the engine, keep these keys — the store methods look records up by exactly these: | Record | Key | Fields | | --------- | ------------------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | | thread | `threadId` | `messages` (array, full transcript) | | run | `runId` | `threadId`, `status`, `startedAt`, `finishedAt?`, `error?`, `usage?`, `parentRunId?`, `subagentRunId?`, `name?`, `sandboxKey?`, `detachedSince?`, `cancelRequested?`, `driverEpoch?` | | interrupt | `interruptId` | `runId`, `threadId`, `status`, `requestedAt`, `resolvedAt?`, `payload`, `response?` | | metadata | `(namespace, key)` | `value` | - Timestamps are **epoch milliseconds** (`number`) in records. Store them however the engine prefers and convert in the mapper. - `(namespace, key)` is a **composite** key. Never join with a separator — `('a:b','c')` and `('a','b:c')` must stay distinct records, and the conformance suite checks it. - Index `runs(threadId, status)`, `runs(threadId, startedAt)`, and `interrupts(threadId, requestedAt)` for the listing paths. If the backend implements `listReclaimable`, also index `runs(status, detachedSince)`. If it implements `listByParentRun`, also index `runs(parentRunId, startedAt)`. - `run.error` is a structured `RunError` (`{ message: string, code?: string }`), not a bare string. `message` is the provider's prose; `code` is the stable, machine-branchable classification an operator filters and groups by. In a SQL-backed table, store it as two columns (`error`, `error_code`) rather than one JSON blob, moved together in `update` so a later code-less failure can never leave a stale `code` from an earlier one behind. `run.status` is one of `'running' | 'interrupted' | 'completed' | 'failed' | 'aborted'`; `'interrupted'` is a pause, not terminal, and only `'completed' | 'failed' | 'aborted'` are terminal. - Extra app-owned columns are fine (a `userId`, audit columns) as long as they are nullable or defaulted. The stores never read columns they do not know about. ## 3. The invariants Getting one of these wrong is the usual source of stuck approvals and wiped history. They are engine-independent: 1. **`saveThread` is a full overwrite**, never an append. The argument is the complete authoritative transcript. 2. **`loadThread` returns `[]`** for an unknown thread, never `null`. 3. **`createOrResume` is insert-if-absent** — an existing `runId` comes back _unchanged_, ignoring the new field values. Resume and double-submit depend on it. After a racy insert, re-read rather than trusting your own write. 4. **`runs.update` on an unknown id is a silent no-op** — it must not throw and must not insert. (Drivers that throw on zero rows affected need the `updateMany`-style call, not the `update`-one-or-throw call.) 5. **`runs.update` distinguishes "field omitted" from "field explicitly cleared" for the durable-run fields** (`sandboxKey`, `detachedSince`, `cancelRequested`, `driverEpoch`). A reattach clears `detachedSince` by passing it explicitly as `undefined` — `update(runId, { detachedSince: undefined })` — and that must write `NULL`, not be silently dropped. Check `'detachedSince' in patch`, never `patch.detachedSince !== undefined`; the latter cannot tell a clear from an omission and leaves every reattached run looking permanently detached to the reaper. Same rule for `cancelRequested` (`false` is a real value, not "unset") and for `sandboxKey` / `driverEpoch`. See `examples/ts-react-chat/src/lib/sqlite-persistence.ts` for the pattern. 6. **`interrupts.create` is insert-if-absent** — never clobber a resolved interrupt back to pending. Every `list*` is ordered by `requestedAt` ascending. 7. **`runs.listReclaimable` uses an inclusive cutoff** (if implemented): `status === 'running' AND detachedSince <= now - ttlMs`. It is a query, not automatic reclamation: `reapDetachedRuns` from `@tanstack/ai-sandbox` is the sweep that consumes it, and the application schedules that sweep. A store without this method cannot be reaped. `runs.findActiveRun` is required; `runs.listByThread`, `runs.listByParentRun`, and `runs.listReclaimable` are optional: implement only what the app needs and leave the rest off the object. `listByParentRun` returns the child runs for one `parentRunId`, oldest `startedAt` first. `reconstructChat` uses that list to put subagent cards back. `createOrResume` copies `parentRunId`, `subagentRunId`, and `name` on the first insert and leaves them unchanged on resume. Row mappers omit absent optionals (`...(row.sandbox_key != null ? { sandboxKey: row.sandbox_key } : {})`) so records compare cleanly against the reference in-memory backend. For a two-column `error`/`error_code` layout, the mapper is `...(row.error != null ? { error: { message: row.error, ...(row.error_code != null ? { code: row.error_code } : {}) } } : {})`. ## 4. Write `src/lib/chat-persistence.ts` Four factories and one assembly. Postgres via `pg` shown here; the shape is the same for any driver. ```ts ignore import { defineAIPersistence } from '@tanstack/ai-persistence' import type { Pool } from 'pg' import type { ChatPersistence, MessageStore, RunStore, } from '@tanstack/ai-persistence' import { pool } from '@/db' function createMessageStore(db: Pool): MessageStore { return { async loadThread(threadId) { const { rows } = await db.query( 'SELECT messages_json FROM chat_threads WHERE thread_id = $1', [threadId], ) return rows[0]?.messages_json ?? [] }, // Full overwrite — `messages` is the complete authoritative transcript. async saveThread(threadId, messages) { await db.query( `INSERT INTO chat_threads (thread_id, messages_json, updated_at) VALUES ($1, $2, $3) ON CONFLICT (thread_id) DO UPDATE SET messages_json = EXCLUDED.messages_json, updated_at = EXCLUDED.updated_at`, [threadId, JSON.stringify(messages), Date.now()], ) }, } } function createRunStore(db: Pool): RunStore { async function get(runId: string) { const { rows } = await db.query( 'SELECT * FROM chat_runs WHERE run_id = $1', [runId], ) return rows[0] ? mapRun(rows[0]) : null } return { get, // Idempotent: an existing runId is returned untouched. async createOrResume(input) { const { runId, threadId, startedAt, status } = input const existing = await get(runId) if (existing) return existing await db.query( `INSERT INTO chat_runs ( run_id, thread_id, status, started_at, parent_run_id, subagent_run_id, name ) VALUES ($1, $2, $3, $4, $5, $6, $7) ON CONFLICT (run_id) DO NOTHING`, [ runId, threadId, status ?? 'running', startedAt, input.parentRunId ?? null, input.subagentRunId ?? null, input.name ?? null, ], ) // Re-read: a concurrent createOrResume may have won the race, and that // row is the authoritative one. const stored = await get(runId) return ( stored ?? { runId, threadId, status: status ?? 'running', startedAt, ...(input.parentRunId !== undefined ? { parentRunId: input.parentRunId } : {}), ...(input.subagentRunId !== undefined ? { subagentRunId: input.subagentRunId } : {}), ...(input.name !== undefined ? { name: input.name } : {}), } ) }, // ... update (no-op on unknown id; sandboxKey/detachedSince/ // cancelRequested/driverEpoch are checked with `'field' in patch`, not // `patch.field !== undefined`, so an explicit `undefined` (a clear) still // writes NULL instead of being silently dropped — status/finishedAt/usage // can use the simpler `!== undefined` check since they are never // explicitly cleared; writes patch.error as two columns, // error = patch.error.message and error_code = patch.error.code ?? null, // together in the same call), // findActiveRun (latest 'running', required), listByThread (ascending // by startedAt, optional), listByParentRun (children of parentRunId, // ascending by startedAt, optional), listReclaimable (status = 'running' // AND detachedSince <= now - ttlMs, inclusive cutoff, optional) } } /** The four chat state stores backed by the app's database. */ export const chatPersistence: ChatPersistence = defineAIPersistence({ stores: { messages: createMessageStore(pool), runs: createRunStore(pool), interrupts: createInterruptStore(pool), metadata: createMetadataStore(pool), }, }) ``` Annotate `ChatPersistence` — bare `AIPersistence` is the all-optional bag and `withPersistence` rejects it. There is no `locks` store: `stores` accepts only `messages`, `runs`, `interrupts`, `metadata`, and anything else throws `Unknown AIPersistence store key`. Coordination is wired separately with `withLocks` (see **ai-core/locks**). If the client is per-request (Workers bindings, request-scoped transactions), export a `chatPersistence()` factory instead of a const and call it inside the handler. ## Engine notes