signature-malleability

Detect ECDSA signature malleability and ecrecover pitfalls — missing low-s (EIP-2) enforcement, unconstrained v, unchecked address(0) from ecrecover, replay across chainId/contract from a missing EIP-712 domain separator, EIP-2098 compact-signature confusion, and signature reuse. Activate whenever code calls ecrecover directly, parses (r,s,v) from bytes, or verifies signed messages without OpenZeppelin ECDSA.