Tagged content part used by AttractorEx.LLM.Message.
The unified client still treats multimodal payloads as pass-through data for provider adapters, but this struct gives requests a stable representation for richer content.
Summary
Types
@type part_type() ::
:text
| :image
| :audio
| :document
| :tool_call
| :tool_result
| :thinking
| :json
Known content part kinds carried by the normalized message model.