Function on_loading_state_change_browser_pane 

pub fn on_loading_state_change_browser_pane(
    state: &Arc<AppState>,
    browser: &Browser,
    can_go_back: bool,
    can_go_forward: bool,
)

Pane-specific on_loading_state_change body. Called from AgentMuxHandler::on_loading_state_change when is_browser_pane == true.

CEF invokes on_loading_state_change whenever the navigation controller’s history state changes — navigation start, navigation commit, and after back/forward. can_go_back / can_go_forward are provided as direct parameters (not queried after the fact), so they’re guaranteed to reflect the real committed state rather than the pre-commit race window.