Function apply_srv_window_workspace_changed 

fn apply_srv_window_workspace_changed(
    wstore: &WaveStore,
    window_id: &str,
    workspace_id: &str,
) -> Result<(), Box<dyn Error>>

Phase E.5 — same shape as apply_srv_window_opened for the upsert behavior; separate function for log-clarity since the emitted event is distinct.