Idempotency and Deduplication

Fulfiro processes the same event multiple times safely. This matters because webhooks can arrive more than once (WooCommerce retries on timeout), and background jobs can be re-queued after crashes.

Webhook deduplication

WooCommerce webhooks include a delivery ID. Fulfiro deduplicates using two layers:

1. Redis SETNX -- Fast-path check. If the delivery ID exists in Redis, the webhook is skipped immediately.
2. Database unique constraint -- Authoritative backup. If Redis misses the dedupe (e.g., Redis restart), the database constraint prevents duplicate processing.

Sync idempotency

Delta syncs use the modified_after timestamp. Processing the same product twice is safe because it is an upsert operation -- the product record is updated to match the latest WooCommerce data.

Stock push idempotency

Outbound stock pushes set an absolute quantity (not a delta). Pushing the same value twice has no effect. This means retried pushes are inherently safe.

Job queue deduplication

BullMQ jobs include a job ID derived from the operation. If a job with the same ID is already in the queue or recently completed, the duplicate is discarded.

Related: Sync Architecture | Webhooks | Stock Consistency

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