happier-profile-and-optimize

# Happier Profile and Optimize Use this skill for any work whose success is a measured cost, not a behavior: slow open/foreground/navigation, jank, hangs, startup, memory, render churn, a query that got slow, or verifying somebody's speedup claim. It is the *investigation* method — reach for it once a cost exists. It is deliberately **not** the list of things to watch for while writing code. Those must apply unprompted, at authoring time, long before anyone suspects a problem, so they live in package instructions that are read on every task: `apps/ui/AGENTS.md` → **Performance and continuity** owns the UI write-time invariants (referential stability, narrow subscriptions, component-type stability, high-frequency state placement, dependency-array identity, loop stop conditions, one perf change lands on all platforms). If you are about to restate one of those here, stop and strengthen it there instead. The rules this skill operates under also live elsewhere and are not restated: root `AGENTS.md` → **Product priorities** (name the phase and metric, instrument must be able to see the cost, no ratio without both sides on the same workload and machine state, no blanket memoization) and **Risk-weighted execution**. Read those; do not re-derive them. Route out, do not absorb: - `skills/happier-diagnose` — the incident is a *failure* (error, hang-to-crash, broken session), not a cost. Diagnose first, then return here only if the outcome is a cost. - `skills/happier-testing` — lan...