Summary

• Add explicit regression coverage for CAT finding a2394309-60a7-435e-ab5b-d66efa0364e4.
• Exercise the reported attack sequence: append trailing bytes to the AWS Nitro root cert, compute valid public P-384 hints, attempt to cache the shadow root, then attempt to verify the genuine child CA under that shadow parent.
• Assert the shadow root is not cached and the child cannot be pinned to the attacker-controlled parent hash.

Security

Latest main already blocks this vector before the verifiedParent write: _verifyUncachedCert requires the outer DER object to consume the full submitted buffer, and _verifyCertSignatureWithHints rejects trailing fields inside the certificate sequence.

This PR locks that behavior with a focused regression test for the exact poisoning path.

Tests

• forge test --match-test test_HintedTrailingRootBytesCannotPoisonParentCache -vvv
• forge test