A working engineer's framework for design patterns — the few worth internalizing, the ones to skip, and the principle that makes patterns useful rather than dogmatic.

Two skills that separate senior from junior engineers more than any other: reading code you did not write, and giving useful critique on code you did not author.

The test pyramid is the floor, not the ceiling. Property-based tests, contract tests, mutation testing, and snapshot tests round out a strategy that actually catches regressions.

The discipline of changing legacy code without breaking it: strangler fig, characterization pins, seam analysis, and the courage needed to delete.

The local craft of designing functions and interfaces — parameter choice, return shapes, versioning, deprecation, and the small rules that make APIs survive their callers.