Function begin_gemini_tracer 

pub async fn begin_gemini_tracer(
    trace: &TraceContext,
    provider: &str,
    model: &str,
    transport: TransportKind,
    url: &str,
    exact_sent_bytes: Option<&[u8]>,
    messages: &[SharedMessage],
    system_prompt: Option<&str>,
    tools_schema: &[Value],
) -> Option<RequestTracer>

Begin tracing one Gemini Code Assist request. Delegates to the shared OpenAI-compatible builder (same normalized message walker, no cache section, wire claimed only from exact_sent_bytes). Returns None when tracing is disabled or identity is unrepresentable.