Function create_isolated_request_context 

pub fn create_isolated_request_context(
    state: &Arc<AppState>,
    label: &str,
) -> Option<RequestContext>

Create an isolated CEF RequestContext for a new browser window.

Each browser window needs its own renderer process to get an isolated JavaScript context (own document, own module state, own SolidJS render tree). CEF assigns a separate renderer process when the RequestContext has a unique cache_path. We use <data_dir>/browser-contexts/<label>/ for this.