SveltyCMS uses the transactional outbox pattern so domain events (webhooks, automations, internal pub/sub) are not lost when a write succeeds but side-effect delivery fails (or vice versa).

Flow

1. Write path (collection create/update/delete) uses persistWithOutbox:
   • The entity write is a single atomic statement (INSERT/UPDATE/DELETE — no BEGIN/COMMIT wrapper needed).
   • The outbox emit is scheduled as a queueMicrotask off the response path — never awaited by the caller. (The old “one DB transaction for entity write + emit” wrapper was removed: single-statement writes are natively atomic, and coalesced buffering avoids serializing content writes 1:1 with outbox rows.)
2. Buffered (non-transactional) emits — emit() outside a transaction pushes into an in-memory buffer and bulk-flushes via one insertMany after OUTBOX_BUFFER_FLUSH_MS (25ms) or at 64 events. The event _id (UUID) is stamped at emit time — it is part of the emit contract and equal to the stored id.
3. Event types: entry:create | entry:update | entry:delete.
4. afterMutation invalidates cache and publishes entryUpdated; on the main create/update/delete path it passes skipOutbox: true (the outbox event was already emitted by persistWithOutbox). Callers that bypass persistWithOutbox fall back to the afterMutation emit.
5. Background outboxService.startPolling() (hooks cold-start) runs processBatch() — which first flushes the emit buffer so milliseconds-old buffered events are included in the tick.
6. Delivery: internal pubSub + optional webhookService.trigger for mapped event types.
7. Success → status: delivered; failure → exponential backoff retry; after 5 attempts → failed.

getPendingCount() reports the true backlog: persisted status: pending rows plus events still sitting in the emit buffer.

Storage

Adapter	Table / collection
SQLite / PostgreSQL / MariaDB	svelty_outbox (migrations + Drizzle schema)
MongoDB	svelty_outbox model (OutboxEvent)

API

import { outboxService } from "@src/services/outbox";

await outboxService.emit(
  "entry:create",
  "entry",
  entryId,
  { collection, data },
  tenantId,
  { transaction }, // optional — same DB transaction as the write
);

await outboxService.processBatch(50);
await outboxService.cleanup(olderThanISO);

Backoff

outboxBackoffMs(attempts) → 1s, 2s, 4s, … capped at 5 minutes, based on updatedAt after each failure. Pending events inside the window are skipped until ready.

Kill switches

Env	Effect
DISABLE_OUTBOX=true	Skip emit + polling

DISABLE_OUTBOX is the only service-level kill switch — ambient benchmark env flags (BENCHMARK=true) no longer disable outbox emits; they only prevent hooks.server.ts from starting the background poller during benchmark cold-start.

Tests

• Unit: tests/unit/services/outbox-service.test.ts
• Integration: tests/integration/api/outbox-plugin-storage.test.ts
• Testing API: outbox-emit, outbox-process-batch, outbox-tx-rollback, …

Implementation

• Service: src/services/outbox/outbox-service.ts
• Boot: hooks.server.ts → outboxService.startPolling(5000)
• Emit: collections-namespace.ts persistWithOutbox (+ afterMutation fallback)