## Context

QUIC stream writes complete before peer receipt. The previous gateway avoided losing its last control frame by waiting for client-owned connection closure; immediate gateway closure reproduced event loss. `control.ack.v1` is already reliable and bidirectional, so no new flow is needed.

## Goals / Non-Goals

**Goals:**

- Represent peer receipt of the one terminal control event.
- Keep the message bounded, direction-specific, and independent of provider data.

**Non-Goals:**

- General acknowledgements, retries, lifecycle state, or provider transport semantics.
- Changes to JSON schemas or generated bindings.

## Decisions

- Assign client-direction `VGF1` type `0x03` with an empty payload to terminal receipt.
- Permit it only after a terminal event; the Data Plane enforces session state and deadline.
- Preserve all existing message bytes and meanings.

## Risks / Trade-offs

- [Older clients do not send the receipt] → The gateway closes at its bounded receipt deadline; compatibility does not transfer tunnel ownership back to the client.
- [A stale receipt is replayed] → The gateway rejects receipts outside the single awaiting-terminal state.