createInstantMessage abstract method
Creates an instant message from envelope (header) and content (body).
Combines routing metadata (envelope) with message payload (content) to form a complete, unencrypted instant message.
@param head - Message envelope (routing metadata: sender/receiver/time)
@param body - Message content (payload: text, file, command, etc.)
@return Complete InstantMessage instance
Implementation
InstantMessage createInstantMessage(Envelope head, Content body);