EntryCategories asked every core in turn: 3.8 million proofs for 7,430
entries. ProofIndex looks each key up once, and verify --all --json is
byte-identical (24 s to 17 s). generate_site and generate_readme now share
one coverage, cached in tmp/coverage-cache keyed by its inputs, so the
README step drops from 25 s to 3 s.
