Function apply_window_meta_updated 

fn apply_window_meta_updated(
    wstore: &WaveStore,
    window_id: &str,
    meta_patch: &Value,
) -> Result<(), Box<dyn Error>>

Phase E.5.x (issue #855) — apply a meta-patch to a window’s meta map. Same shape as apply_workspace_meta_updated. Silent no-op if the window doesn’t exist in wstore (preserves the idempotency contract — duplicate or stale events fold to no-op).