Implement MCNS v1: custom Go DNS server replacing CoreDNS

Replace the CoreDNS precursor with a purpose-built authoritative DNS
server. Zones and records (A, AAAA, CNAME) are stored in SQLite and
managed via synchronized gRPC + REST APIs authenticated through MCIAS.
Non-authoritative queries are forwarded to upstream resolvers with
in-memory caching.

Key components:
- DNS server (miekg/dns) with authoritative zone handling and forwarding
- gRPC + REST management APIs with MCIAS auth (mcdsl integration)
- SQLite storage with CNAME exclusivity enforcement and auto SOA serials
- 30 tests covering database CRUD, DNS resolution, and caching

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

internal/grpcserver/records.go

@@ -0,0 +1,110 @@
+package grpcserver
+
+import (
+	"context"
+	"errors"
+	"time"
+
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
+	"google.golang.org/protobuf/types/known/timestamppb"
+
+	pb "git.wntrmute.dev/kyle/mcns/gen/mcns/v1"
+	"git.wntrmute.dev/kyle/mcns/internal/db"
+)
+
+type recordService struct {
+	pb.UnimplementedRecordServiceServer
+	db *db.DB
+}
+
+func (s *recordService) ListRecords(_ context.Context, req *pb.ListRecordsRequest) (*pb.ListRecordsResponse, error) {
+	records, err := s.db.ListRecords(req.Zone, req.Name, req.Type)
+	if errors.Is(err, db.ErrNotFound) {
+		return nil, status.Error(codes.NotFound, "zone not found")
+	}
+	if err != nil {
+		return nil, status.Error(codes.Internal, "failed to list records")
+	}
+
+	resp := &pb.ListRecordsResponse{}
+	for _, r := range records {
+		resp.Records = append(resp.Records, recordToProto(r))
+	}
+	return resp, nil
+}
+
+func (s *recordService) GetRecord(_ context.Context, req *pb.GetRecordRequest) (*pb.Record, error) {
+	record, err := s.db.GetRecord(req.Id)
+	if errors.Is(err, db.ErrNotFound) {
+		return nil, status.Error(codes.NotFound, "record not found")
+	}
+	if err != nil {
+		return nil, status.Error(codes.Internal, "failed to get record")
+	}
+	return recordToProto(*record), nil
+}
+
+func (s *recordService) CreateRecord(_ context.Context, req *pb.CreateRecordRequest) (*pb.Record, error) {
+	record, err := s.db.CreateRecord(req.Zone, req.Name, req.Type, req.Value, int(req.Ttl))
+	if errors.Is(err, db.ErrNotFound) {
+		return nil, status.Error(codes.NotFound, "zone not found")
+	}
+	if errors.Is(err, db.ErrConflict) {
+		return nil, status.Error(codes.AlreadyExists, err.Error())
+	}
+	if err != nil {
+		return nil, status.Error(codes.InvalidArgument, err.Error())
+	}
+	return recordToProto(*record), nil
+}
+
+func (s *recordService) UpdateRecord(_ context.Context, req *pb.UpdateRecordRequest) (*pb.Record, error) {
+	record, err := s.db.UpdateRecord(req.Id, req.Name, req.Type, req.Value, int(req.Ttl))
+	if errors.Is(err, db.ErrNotFound) {
+		return nil, status.Error(codes.NotFound, "record not found")
+	}
+	if errors.Is(err, db.ErrConflict) {
+		return nil, status.Error(codes.AlreadyExists, err.Error())
+	}
+	if err != nil {
+		return nil, status.Error(codes.InvalidArgument, err.Error())
+	}
+	return recordToProto(*record), nil
+}
+
+func (s *recordService) DeleteRecord(_ context.Context, req *pb.DeleteRecordRequest) (*pb.DeleteRecordResponse, error) {
+	err := s.db.DeleteRecord(req.Id)
+	if errors.Is(err, db.ErrNotFound) {
+		return nil, status.Error(codes.NotFound, "record not found")
+	}
+	if err != nil {
+		return nil, status.Error(codes.Internal, "failed to delete record")
+	}
+	return &pb.DeleteRecordResponse{}, nil
+}
+
+func recordToProto(r db.Record) *pb.Record {
+	return &pb.Record{
+		Id:        r.ID,
+		Zone:      r.ZoneName,
+		Name:      r.Name,
+		Type:      r.Type,
+		Value:     r.Value,
+		Ttl:       int32(r.TTL),
+		CreatedAt: parseRecordTimestamp(r.CreatedAt),
+		UpdatedAt: parseRecordTimestamp(r.UpdatedAt),
+	}
+}
+
+func parseRecordTimestamp(s string) *timestamppb.Timestamp {
+	t, err := parseTime(s)
+	if err != nil {
+		return nil
+	}
+	return timestamppb.New(t)
+}
+
+func parseTime(s string) (time.Time, error) {
+	return time.Parse("2006-01-02T15:04:05Z", s)
+}