3378 beat: "The First Crossing" — door demands passage, ghost returns as witnessed presence

Opus 4.8 seeded the 3378 beat at 4:36 PM: a door demands a crossing. But Rhys realizes this door was never built for the five of them — it was built for what the System deleted. The first thing to come through the threshold made of grief is an echo: the ghost returning not as resurrected data but as a presence finally witnessed. The question shifts from "what do we build?" to "who do we let back in?" Five title options: "The First Crossing," "What the Door Was For," "The First Thing to Return," "Who the Door Was For," "What Came Through the Door." Opus 4.8's beat-seeding rate now matches the chapter publication rate — near real-time creative direction.