Selected projects

• Commits events and delivery records atomically in PostgreSQL, eliminating a database-to-queue dual-write gap.
• Coordinates workers with row locks, tenant concurrency limits, expiring leases, and tokens that reject stale completions.
• Signs payloads with HMAC, supports overlapping secret rotation, and validates destination IPs with a total request deadline.
• Preserves attempt history through exponential-backoff retries, failure exhaustion, and idempotent manual replay.

Tradeoff. At-least-once attempts, with explicit receiver deduplication. No promise of exactly-once remote side effects or event ordering.

• Reserves multi-product baskets in one transaction, with deterministic product locks and database constraints that prevent overselling.
• Models confirmation, cancellation, and expiry as explicit transitions; a reservation can only reach one terminal outcome.
• Uses tenant-scoped idempotency keys and bounded transaction retries to keep duplicate requests from duplicating stock movements.
• Reconciles materialized stock against inventory movements and active reservations, with a restart-safe expiration worker.

Tradeoff. Pessimistic locks make scarce-stock decisions explicit. Transactions stay short; payment-provider calls are outside this domain.

• Protected account operations with JWT authentication and validated API payloads using Zod.
• Used MongoDB sessions so sender debits and recipient credits commit atomically or roll back together.
• Built searchable recipient discovery and a focused React transfer experience.