id

Identity within one transcript, and the key a list renderer is meant to use.

Unique across UiTranscript.messages -- Compose's LazyColumn throws outright on a duplicate key, so this is a guarantee a renderer is entitled to lean on rather than a coincidence. The producer is what upholds it: agui-core disambiguates on sight, because the wire promises nothing of the sort and a run that renumbers its message ids from one is an ordinary thing for an agent to do.

Usually the protocol message id this turn opened under, and equal to it whenever nothing forced a rename. It is not the field to correlate against the wire: a turn folds several protocol messages together, and each part keeps its own protocol id (TextPart.messageId and its siblings) for exactly that.