docs(protocol): archive terminal receipt contract

2026-07-30 10:50:57 +07:00
parent ec15279b42
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+## 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.