Taking a product from an empty repository to production — React or Next.js on the front, NestJS, Hono or Express behind it, on PostgreSQL or MongoDB.
Designing tenancy models, role and attribute-based authorization, and audit trails for B2B platforms that serve many companies from one codebase.
Profiling slow endpoints, eliminating N+1 queries, designing indexes, and adding caching where it actually pays — with the before and after measured, not guessed.