rule-gate-integritylisted

# A gate that cannot fail is not a gate These four failure modes were hit independently by two sessions on the same day, working on unrelated problems — a mutation harness for a token generator, and a test-vacuity sweep across a plugin marketplace. Both arrived here the hard way. Each one produces a **green result that means nothing**, and each is invisible from the summary line. ## 1. Run the real thing. Never grade a copy. A check that rebuilds what it is checking grades its own reconstruction. It passes happily while the shipped artefact emits something else. - A token gate must **run the real generator in `--check`** and read its exit code, not assemble the CSS it expects and diff that. - A retry-policy test must **import the real function**. One in a production repo reimplemented `withTransientRetry` inline; the copy was faithful when compared, which is the most dangerous state for a copy to be in — it looks like evidence. If speed is the reason for the copy, make the *slow part* injectable instead. A 2s/8s/32s backoff became an optional parameter that production never passes; the real function then runs in milliseconds under test. The same trap has a timing form: a gate that regenerates an artefact and *then* reads it compares the generator against its own output and is green forever. One production repo shipped a stale manifest twice that way, with preflight passing both times. Snapshot what was **on disk** — what a commit would actually have shipped — befo