Identifier for a message, unique among messages of the same type within a session.
Each message type, such as user messages, agent messages, and agent thoughts,
has its own ID space: messages of different types may share an ID and remain
distinct messages.
Identifier for a message, unique among messages of the same type within a session.
Each message type, such as user messages, agent messages, and agent thoughts, has its own ID space: messages of different types may share an ID and remain distinct messages.