Function plan_tool_call 

async fn plan_tool_call(
    conn: &mut PgConnection,
    user_context: &ChatbotTurnContext,
    tool_name: &str,
    arguments: &str,
) -> ChatbotResult<PlannedToolCall>

Decides who answers a call the model made, before anything about it is stored.

A client tool’s authorization and arguments are both checked here, not when an answer arrives: nothing can answer a call the tool would reject or the caller may not make, so it has to fail while the turn can still hand the LLM a failure output. The server tools are checked the same way inside call_chatbot_tool. Errors on a rejection the turn cannot survive — see recover_or_terminate.