Function handle_update_window_meta 

pub(super) fn handle_update_window_meta(
    state: &mut State,
    window_id: String,
    meta_patch: Value,
) -> Vec<Event>

Phase E.5.x (issue #855) — apply a meta-patch to a window. Pass- through to Event::WindowMetaUpdated; the persist subscriber performs the merge against wstore. Same shape as handle_update_workspace_meta — reducer state does NOT track window meta, the migration property is “every mutation goes through the reducer’s broadcast bus” so the WaveObjUpdate bridge can fan out to the frontend.

The validation is best-effort: reducer state’s windows map only holds windows for which a workspace mapping has been registered (via handle_create_window). Windows created via wcore-direct paths (legacy bootstrap) won’t appear there but still exist in wstore. So we don’t error on missing — the persist subscriber’s apply_window_meta_updated will silently no-op if the window genuinely doesn’t exist in wstore either, matching the idempotency contract for the bridge to broadcast (or skip).