Update ERC-7786: Add messageId to IERC7786Receiver.executeMessage

Merged by EIP-Bot.

ERCS/erc-7786.md

@@ -115,13 +115,16 @@ A **Destination Gateway** is a contract that implements a protocol to validate m
 
 The protocol MUST ensure delivery of a sent message to its **receiver** using the `IERC7786Receiver` interface (specified below), which the receiver MUST implement.
 
-Once the message can be safely delivered (see Properties), the gateway MUST invoke `executeMessage` with the message contents.
+Once the message can be safely delivered (see Properties), the gateway MUST invoke `executeMessage` with the message identifier and contents, unless the sender or the receiver explicitly requested otherwise.
+
+The `messageId` MUST be either empty or unique (for the calling gateway) to the message being relayed. The format of this identifier is not specified, and the gateway can use it at its own discretion. For example it can be an identifier of the `MessagePosted` event that created the message.
 
 The gateway MUST verify that `executeMessage` returns the correct value, and MUST revert otherwise.
 
 ```solidity
 interface IERC7786Receiver {
     function executeMessage(
+        string calldata messageId, // gateway specific, empty or unique
         string calldata sourceChain, // [CAIP-2] chain identifier
         string calldata sender, // [CAIP-10] account address
         bytes calldata payload,