Ruthless bottleneck destroyer

A check earns what it costs. Every test, hook, gate and CI job has five properties, each with its own proof:

Property	Bad state	Proof
It has something to catch	a check of code nothing uses; a check repeating what a tool in the gate already refuses; a check standing in for a type, import, schema or generator that would make the bad state impossible to write	a search of every place a user could live finds one; the break gets past every tool; a stated reason the owner upstream cannot refuse it
It catches its break	a test that passes whether or not the behaviour happened	break the rule on purpose; the test fails
It is the only one that does	two tests, or two stages, prove the same thing	the same break: exactly one test fails
It runs only when its inputs change	reruns on unchanged code, coarse cache keys, a second checkout rebuilding	an unchanged rerun does zero work; one changed input redoes only its own unit
It costs only what its claim needs	setup rebuilt per test, sleeps, process spawns, hardware thrown at repeats	the per-test time limit the runner enforces, and a check that refuses each slow shape

ruthless-bottleneck-destroyer