Led the frontend test migration from Karma/Jasmine to Vitest with Playwright coverage — cutting CI time and moving the codebase onto a modern TypeScript/ESM toolchain in the same pass. A test suite is a claim about what the system guarantees; a slow one is a claim nobody reads.

Underneath the tools: system design, distributed systems, concurrency, and observability. First principles, then tools. A new domain — Kubernetes resource tuning, LLM context engineering, gRPC — means understanding the underlying model before reaching for the abstraction. It slows down the first hour and speeds up everything after.

Code review and technical mentoring close the list because neither is a soft skill. Setting technical direction for a cross-seniority team — including engineers senior in title — happens through structured demos on JavaScript semantics, async patterns, and RxJS, not through org charts.