Make post-quantum handshakes hybrid only: drop ix_psk2_mlkem1024, need a v3 certificate, and leave a classical msg1 crossing a hybrid one unanswered

handshake/patterns.go

@@ -12,16 +12,13 @@ import (
 type msgFlags struct {
 	expectsPayload bool // message carries indexes and time
 	expectsCert    bool // message carries the certificate
-	kemKey         bool // payload carries an ML-KEM encapsulation key
-	kemCiphertext  bool // message is prefixed with the ML-KEM ciphertext for the peer's key
 }
 
 // subtypeInfo bundles the noise pattern with the per-message flags for a
 // given handshake subtype.
 type subtypeInfo struct {
-	pattern      noise.HandshakePattern
-	pskPlacement int // noise psk modifier position, 0 means no psk token
-	msgs         []msgFlags
+	pattern noise.HandshakePattern
+	msgs    []msgFlags
 
 	// kem is the KEM of a hybrid pattern, nil for any other. Hybrid patterns
 	// carry composite static keys and need version 3 certificates on both
@@ -41,22 +38,6 @@ var subtypeInfos = map[header.MessageSubType]subtypeInfo{
 		},
 	},
 
-	// IX with an ephemeral ML-KEM-1024 exchange:
-	//   msg1 (I->R): payload + cert + encapsulation key
-	//   msg2 (R->I): ciphertext || noise(payload + cert)
-	// The responder encapsulates after reading msg1 and mixes the shared secret in
-	// through the psk2 token at the end of msg2. The ciphertext travels outside the
-	// noise message because the initiator needs the secret before it can process
-	// that token.
-	header.HandshakeIXPSK2MLKEM1024: {
-		pattern:      noise.HandshakeIX,
-		pskPlacement: 2,
-		msgs: []msgFlags{
-			{expectsPayload: true, expectsCert: true, kemKey: true},
-			{expectsPayload: true, expectsCert: true, kemCiphertext: true},
-		},
-	},
-
 	// Hybrid IX (github.com/DefinedNet/noise, see its PQ_RESEARCH.md):
 	//   msg1 (I->R): e, s                          payload + cert
 	//   msg2 (R->I): ekem, skem, e, ee, se, s, es  payload + cert