After running hundreds of senior interviews, the signal is rarely about algorithms. It is about judgment, blast radius, and how someone reasons when the problem is underspecified.

Why dual writes to your database and Kafka silently lose events, and how the transactional outbox pattern fixes it in production.

How we built an idempotency layer on Postgres that survives client retries, gateway timeouts, and concurrent requests without double-charging anyone.

How we eliminated static cloud credentials across CI, EKS, and developer laptops using OIDC federation and dynamic Vault secrets.

We were spending ~$30k/month on AWS. Over two quarters we cut it ~45%. Most savings were hiding in data-transfer costs nobody looks at, and several wins were cost and security fixes at once.