Unique message identifier
Type of message
Sender agent ID
Optional fromSender's role in the agency
Optional toTarget agent ID (null for broadcasts)
Optional toTarget role (for role-based routing)
Optional agencyAgency context
Message content
Message priority
Timestamp when sent
Optional expiresExpiration time for time-sensitive messages
Optional inIf this is a reply, the original message ID
Optional threadThread/conversation ID for related messages
Optional metadataAdditional metadata
Optional requiresWhether delivery confirmation is required
A message sent between agents.