ai.PromptMessage$stream

The chat role, e.g. "system", "user", or "assistant". Empty for role-less content.

The message's rendered text. Media parts use a readable placeholder.

Ordered structural content. Provider clients use this instead of the readable content projection so media survives prompt rendering.

Per-message provider directives, carried verbatim from the ai.Role.metadata of the ${role(...)} marker that opened this message — Anthropic cache_control, for example. Empty when the message carried none.