Function create_tool_call 

pub fn create_tool_call(
    tool_use_id: &str,
    name: &str,
    input: &Value,
    parent_tool_use_id: Option<&str>,
) -> ToolCall

Mirrors createToolCall(toolUseId, name, input, parentToolUseId). Builds the rich ToolCall envelope upstream emits when the assistant first invokes a tool.