Step 2: the verifier should compare the provenance with expected values for at least the builder identity (to stop the right code being built on the wrong platform), the canonical source repository (to stop builds from forks), the buildType (so parameters are read as intended) and the externalParameters (to stop unofficial behaviour being injected). Unrecognised external parameters should cause failure; a parameter may accept a range of values only where every value in it is known to be safe. The package ecosystem may approve a list of parameters to ignore. Step 3 (optional): check resolved dependencies recursively as far as wanted, which the specification does not require and which usually needs a trimming or exception rule; a verification summary attestation can record earlier results to make this cheaper.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.