These contracts send messages to each other directly via the Arbitrary Messaging Bridge.
According to Gnosis Chains Security Considerations for Receiving a Call via the AMB, its the receivers responsibility to take measures against replay attacks (or accidental message replay) by the AMB:
This documentation seems to be outdated as the transactionHash no longer serves to uniquely identify a message, and replay protection seems to be implemented on both the Home and Foreign ends of the bridge (also in the live contracts).
Nevertheless, it is advisable to verify that the functionality of the AMB is correctly understood and to consult with the upstream maintainers regarding this section of the documentation.
Alternatively, implement replay protection to be safe.
