Add OpRegister: cert-only registration without PoW

New flow: register -> OpRegister(pubKey) -> OpIdentity(number+cert). Reconnect: OpGetChallenge -> OpAuthCert(cert+sig). PoW eliminated from client flow.

internal/server/server.go

@@ -217,6 +217,8 @@ func (s *Server) handleStream(ctx context.Context, stream *quic.Stream, sess *Se
 			s.handleReroll(sess)
 		case types.OpAuthCert:
 			s.handleAuthCert(sess, frame.Payload)
+		case types.OpRegister:
+			s.handleRegister(sess, frame.Payload)
 		case types.OpDial:
 			if !sess.IsAuthenticated() {
 				sendOpError(st, types.ErrInvalidRequest, "not authenticated")
@@ -367,6 +369,45 @@ func (s *Server) handleAuthCert(sess *Session, payload []byte) {
 		zap.String("number", ident.Number))
 }
 
+func (s *Server) handleRegister(sess *Session, payload []byte) {
+	if len(payload) < 32 {
+		sendOpError(sess.Stream(), types.ErrInvalidRequest, "invalid pubkey")
+		return
+	}
+
+	var pubKey [32]byte
+	copy(pubKey[:], payload[:32])
+
+	if _, err := s.identMgr.GetByPubKey(pubKey); err == nil {
+		sendOpError(sess.Stream(), types.ErrInvalidRequest, "already registered")
+		return
+	}
+
+	ident, err := s.identMgr.Allocate(pubKey)
+	if err != nil {
+		sendOpError(sess.Stream(), types.ErrInternal, err.Error())
+		return
+	}
+
+	certDER, err := s.ca.IssueCert(ident.Number, ed25519.PublicKey(pubKey[:]), s.cfg.CA.Validity)
+	if err != nil {
+		sendOpError(sess.Stream(), types.ErrInternal, "cert issuance failed")
+		return
+	}
+	ident.CertDER = certDER
+
+	sess.Authenticate(ident.Number, pubKey, certDER)
+	s.Register(sess, ident.Number)
+
+	payload = marshalIdentityResponse(ident.Number, certDER, s.ca.CACertPEM())
+	if st := sess.Stream(); st != nil {
+		st.WriteFrame(byte(types.OpIdentity), payload)
+	}
+
+	s.logger.Info("Client registered",
+		zap.String("number", ident.Number))
+}
+
 func (s *Server) handleReroll(sess *Session) {
 	if !sess.IsAuthenticated() {
 		sendOpError(sess.Stream(), types.ErrInvalidRequest, "not authenticated")

pkg/types/opcode.go

@@ -9,6 +9,7 @@ const (
 	OpIdentity     OpCode = 0x04
 	OpReroll       OpCode = 0x05
 	OpAuthCert     OpCode = 0x06
+	OpRegister     OpCode = 0x07
 
 	OpDial       OpCode = 0x10
 	OpRing       OpCode = 0x11