Six refusals were disabled one at a time. Five died: the three §20
identity checks, downgrade, signature and substitution, and both key-log
fork checks. This one survived all 719 engine and 473 client tests.
`verifyInclusion` ends with `rootFromInclusion(...) ?: return false`.
That line is what turns "this proof reconstructs nothing" into a
refusal, and flipping it to `?: return true` broke nothing.
It hid because the suite does assert the null cases, on
`rootFromInclusion` directly:
assertNull(KeyLog.rootFromInclusion(leaf, size, size, proof))
assertNull(KeyLog.rootFromInclusion(leaf, -1, size, proof))
The primitive was tested and the wrapper everything calls was not. With
that line wrong, a proof whose shape is wrong, a bad index, a truncated
path, a spare node, would have verified, which is the §19.2 refusal
itself.
The new test drives `verifyInclusion` with all four shapes and asserts
the published proof still verifies first, so the refusals cannot be
satisfied by a verifier that always says no.
`scripts/mutate.py` ships the harness, as in the engine and the relay.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
