how to deal with reorg message on source chain?

[xiaoch05]

Helix uses the messageId of the underlying message as the unique identifier of the transaction, so when a reorg occurs on the source chain, it is possible that the same transaction will generate a different messageId to be sent to the destination chain.

For example, messageId is generated by hash(nonce, payload), the nonce is stored in the contract and is incremented.

• UserA sends a transaction with nonce = 1 to a forked chain.
• UserB sends a transaction that takes up nonce = 1 on the canonical chain
• and then UserA's transaction is immediately packaged on the canonical chain and takes up nonce = 2.

At this point, UserA's transaction generates different messageId on the forked chain and the canonical chain, which will be considered as different messages on the target chain, generating a double spend.