Transactions

Byline exposes a request-scoped withTransaction capability so that several database commands can commit or roll back atomically, without threading a transaction handle through every signature. The boundary is owned by the service layer; commands resolve their executor through an AsyncLocalStorage-propagated transaction. Its primary consumer is the document-level audit log, where each audited write-point wraps its mutation and audit.append in one transaction so the change and its audit row commit together.

The problem

Before this capability, every db.commands.* mutation owned its own transaction internally (this.db.transaction(...) — 6 sites, all in packages/db-postgres/src/modules/storage/storage-commands.ts). Each command was atomic in isolation, but two commands could not be composed into one transaction. That's a gap the moment a single logical operation must write two things atomically:

• The audit log (the forcing case). A document-level change — a path edit, a status transition, a delete — and its audit-log row must commit together. The one unacceptable outcome for an auditability feature is a change that succeeds while its audit row silently fails to write. See Auditability.
• Uploads (the half-case — see below). The media record and its related rows should commit together.

The pattern — AsyncLocalStorage propagation

Ported from the Modulus project (whose registry.ts Byline already shares), and the same AsyncLocalStorage mechanism the logger already uses (packages/core/src/lib/logger.ts → withLogContext). Two small pieces:

const transactionALS = new AsyncLocalStorage<DB>()

// Returns the ambient transaction if one is open in this async context,
// otherwise the connection pool.
class DBManagerImpl {
  constructor(private deps: { dbPool: DB }) {}
  get(): DB {
    return transactionALS.getStore() ?? this.deps.dbPool
  }
}

// Opens a real transaction and runs `fn` with that tx bound to the ALS,
// so every `db.get()` *during* `fn` transparently sees the same tx.
class TXManagerImpl {
  constructor(private deps: { db: DBManager }) {}
  withTransaction<T>(fn: () => Promise<T>): Promise<T> {
    return this.deps.db.get().transaction((tx) => transactionALS.run(tx, fn))
  }
}

The win: commands never thread a tx parameter. They obtain their executor from db.get(); the transaction boundary is owned one level up, by the service. Compose by wrapping:

await txManager.withTransaction(async () => {
  await db.commands.documents.setDocumentStatus(...)            // the mutation
  await db.commands.audit.append({ action: 'document.status.changed', ... })
})
// both run on the ambient tx → commit together, or roll back together

The audit write lives in the service (where the actor and before/after already are); the adapter only gains a dumb audit.append command that inserts a row. The storage layer never learns the word "audit". See the document-level audit log for the consuming side.

Boundary placement

withTransaction is exposed today as an adapter capability (IDbAdapter.withTransaction, wired in pgAdapter). Ownership of the boundary — deciding what spans a transaction — belongs to the service layer: each audited lifecycle service wraps its mutation + audit.append in db.withTransaction(...). Commands stay transaction-agnostic — correct whether called standalone (their statements run on the pool) or inside a withTransaction (they join the ambient tx).

When get() already returns a tx and a command opens its own .transaction(...), Drizzle issues a SAVEPOINT (nested transaction): an inner failure rolls back to the savepoint, an outer failure rolls back everything — the correct semantics. The integration test (storage-transactions.test.ts) confirms commit-together and roll-back-together across nested command transactions.

Adoption

The capability was added without a big-bang rewrite of the adapter. In place:

1. DBManager / TXManager (packages/db-postgres/src/lib/db-manager.ts), constructed in pgAdapter and wired to expose withTransaction.
2. Both storage command-builder classes (CollectionCommands, DocumentCommands) converted in one stroke via a private get db() getter that resolves this.dbManager.get() — so every command-builder method, not just the four the audit log needs, transparently joins an ambient transaction with zero call-site changes.

Still on the raw pool (migrate opportunistically): the query builders and the counter commands. Reads don't need to join the audit transaction, and counters aren't in any audit unit of work.

The one caveat: an unconverted path won't see the ambient transaction — it silently runs on the pool. Since the command builders are fully converted, this now only means a withTransaction block should not rely on a query or counter call participating. Easy to honour; worth a deliberate check when those paths are eventually wrapped.

DB↔DB vs DB↔external — what this does and does not solve

A sharp line, because conflating the two leads to a wrong design:

• DB ↔ DB (audit + mutation; document + related record): fully solved. Multiple commands, one transaction, atomic.
• DB ↔ external side-effect (file storage + media record): not solved by transactions. You cannot roll back an S3 / filesystem PUT inside a database transaction. That stays a compensation / saga concern — write the file, write the DB record in a transaction, and on DB failure delete the file (the upload flow already carries partial compensation: shouldCreateDocument: true "rolls back storage on failure", see File / Media Uploads). This work makes the DB side of uploads atomic and tidier; the file↔DB boundary still needs compensation. "Transactions fix uploads" is not a promise this makes.

Serverless / HTTP-gateway databases — the contract seam

AsyncLocalStorage is transport-agnostic — it propagates whatever value you store, transaction handle or not. The real constraint is one level down: interactive transactions require a stateful session bound to one connection for the life of the withTransaction(fn) callback (open tx → run arbitrary app code that issues several statements → commit/rollback).

Serverless DB services that expose only a per-request HTTP/API gateway — Neon's HTTP driver, Cloudflare D1, PlanetScale's HTTP driver — generally cannot offer interactive transactions; they accept single queries or pre-batched arrays, not a callback with app logic interleaved. Drizzle reflects this: db.transaction(callback) exists for session-capable drivers (node-postgres, postgres.js, Neon WebSocket, …) and is absent / throws on pure-HTTP drivers. (Byline ships exactly one adapter today — @byline/db-postgres on drizzle-orm/node-postgres + a real pg.Pool — which is fully interactive-transaction-capable, so the pattern works now with zero compromise.)

The decisions this forces at the db contract seam, made cheaply now so a future adapter has a clear target:

1. Transaction machinery lives in the adapter (@byline/db-postgres), never in @byline/core. Transactions are inherently driver-specific; DBManager / TXManager are adapter internals. Core stays transport-agnostic — consistent with guard rail 3 in Core Composition.
2. withTransaction is an adapter capability on the contract. Services depend on IDbAdapter.withTransaction(fn), not on Postgres specifically, so a future Fastify/serverless adapter has an explicit method to satisfy or reject.
3. Non-support must be loud, never silent. An adapter that cannot provide interactive transactions must throw on withTransaction (or fail a boot-time capability check), not degrade to running fn without atomicity. Audit atomicity is the whole point; silently non-atomic audit writes are worse than no feature. A non-transactional adapter is a deployment the operator must consciously accept (and audit atomicity degrades, documented and guarded).
4. Emulation is YAGNI. A command-buffer / outbox that batches statements to flush as one HTTP request at "commit" is conceivable for HTTP-batch drivers — but it isn't worth designing until a second, genuinely serverless adapter actually arrives. Same "design against two concrete shapes" discipline used for the stable HTTP transport and the richtext adapter contract.

Code map