Function eval 

pub async fn eval(
    __arg0: State<Arc<AppState>>,
    headers: HeaderMap,
    __arg2: Json<EvalReq>,
) -> (StatusCode, Json<ApiResponse<EvalData>>)

POST /agentmux/browser/eval — run arbitrary JS in the pane’s renderer, return the serialized value.

Thin wrapper over CDP Runtime.evaluate. The script runs in the pane’s JS world (not an isolated context); treat it as arbitrary code execution in whatever origin the pane currently loads.