hotpath: never optimize on vibes

The skill is the discipline: measure → change one thing → measure the same way → report the delta or revert. An optimization without a before/after number is a rumor. Most "obvious" performance work fixes code that wasn't hot and misses the query that was.

Prerequisites

A runnable system plus one measurement path to the complaint (profiler, APM, query log, bundle analyzer, or even time + counters). No measurement path at all → the first deliverable is instrumentation, not optimization (see stop conditions).

Identify the user-visible objective, metric unit, workload, data shape, environment, release/commit, hardware or browser conditions, baseline owner, and acceptable correctness/cost tradeoff. "Fast" is not a metric, and a development-server trace is not a production conclusion.