Ai_provider.ContentSourceResponse content parts returned by model generation.
type t = | Text of {}| Tool_call of {tool_call_type : string;Always "function" for now.
tool_call_id : string;tool_name : string;args : string;Raw JSON string -- consumer decides when to parse.
*)}| Reasoning of {text : string;signature : string option;provider_options : Provider_options.t;}| File of {}