Standard Unstructured Annex

Antoine addresses a potential update concerning taproot annex support, referencing a proposal found at GitHub. The suggestion involves initiating all inputs with an annex, starting with a 1-byte format that combines a zero byte (0x00) with a payload of random data. This approach is recommended to circumvent issues such as the inflation of annex size, which could potentially lower the fee rate of multi-party transactions and lead to congestion in network mempools by making coinjoin transactions difficult to process.

Moreover, Antoine raises a concern about the absence of a policy or rule to cap the maximum size of the annex. Without such a limitation, the same problems of transaction delay and network clogging could persist, given that the annex, being a non-standard taproot data field, currently does not have a maximum size limit. This insight suggests a need for further review and possibly the implementation of transaction-relay policies that would enforce a maximum annex size to mitigate these risks.