docs(openspec): archive terminal receipt repair

openspec/specs/gateway-input-feedback/spec.md

@@ -40,11 +40,15 @@ an implementation-specific release-all provider command.
 The registered bidirectional reliable `control.ack.v1` flow SHALL define an ASCII `VGF1` envelope
 with a direction byte, type byte, big-endian payload length, and exact payload
 bytes. Only host termination, rumble, and HDR feedback SHALL be valid from the
-gateway to the client. Only IDR, FEC/loss feedback, and an empty terminal receipt
-SHALL be valid from the client to the gateway. The terminal receipt SHALL be
-valid only while the same session awaits receipt of its one terminal event and
-MUST NOT be forwarded to the provider. The envelope SHALL contain no provider
-address, certificate, credential, or opaque provider packet.
+gateway to the client. Only IDR, FEC/loss feedback, and client-direction type
+`0x03` with an empty payload as terminal receipt SHALL be valid from the client
+to the gateway. The fixed conformance corpus and every generated or native
+Protocol validator SHALL accept that exact receipt and reject unknown types,
+wrong direction, nonempty receipt bodies, truncation, and length mismatch. The
+terminal receipt SHALL be valid only while the same session awaits receipt of
+its one terminal event and MUST NOT be forwarded to the provider. The envelope
+SHALL contain no provider address, certificate, credential, or opaque provider
+packet.
 
 #### Scenario: Host termination forwarding
 - **WHEN** the Apollo adapter receives an authenticated host termination packet
@@ -52,7 +56,7 @@ address, certificate, credential, or opaque provider packet.
 
 #### Scenario: Terminal event receipt
 - **WHEN** a client receives the reliable typed terminal event
-- **THEN** it sends the empty terminal receipt and the gateway owns bounded tunnel closure without forwarding the receipt to the provider
+- **THEN** it sends the fixed empty client-direction type `0x03` receipt and the gateway owns bounded tunnel closure without forwarding the receipt to the provider
 
 #### Scenario: Unauthorized or malformed feedback
 - **WHEN** feedback is disabled by policy, has an invalid direction/type/length, contains a forbidden provider field, or sends a terminal receipt outside the awaiting-terminal state