Slate Greeting

Fired when a NORMAL run parks at a checkpoint — the story slate (CP1) or the angles (CP2). The desk narrates whichever just landed with the engine's counsel, so the cards don't appear in silence. Idempotent per session+checkpoint (returns null when nothing applies — intel query, not parked, or already greeted), so the frontend can call it on every CP1/CP2 edge.