feat(graphql): add JS-safe uint64 marshal helpers

Adds MarshalUint64, UnmarshalUint64, and Uint64Marshaler for gqlgen-
compatible uint64 string scalars without a gqlgen dependency.

Co-authored-by: Cursor <cursoragent@cursor.com>

gql_uint64.go

@@ -0,0 +1,55 @@
+package dbx
+
+import (
+	"fmt"
+	"io"
+	"strconv"
+)
+
+// Uint64Marshaler wraps a uint64 for GraphQL JSON output as a string scalar.
+type Uint64Marshaler uint64
+
+// MarshalGQL writes the uint64 as a JSON string for gqlgen compatibility.
+func (u Uint64Marshaler) MarshalGQL(w io.Writer) {
+	fmt.Fprintf(w, "\"%d\"", uint64(u))
+}
+
+// MarshalUint64 marshals a uint64 as a JSON string to avoid JavaScript
+// precision loss for integers larger than 2^53-1.
+func MarshalUint64(i uint64) Uint64Marshaler {
+	return Uint64Marshaler(i)
+}
+
+// UnmarshalUint64 unmarshals a uint64 from a JSON string or number.
+func UnmarshalUint64(v any) (uint64, error) {
+	switch value := v.(type) {
+	case string:
+		if value == "" {
+			return 0, nil
+		}
+		n, err := strconv.ParseUint(value, 10, 64)
+		if err != nil {
+			return 0, fmt.Errorf("invalid uint64 string: %w", err)
+		}
+		return n, nil
+	case int:
+		if value < 0 {
+			return 0, fmt.Errorf("invalid negative uint64: %d", value)
+		}
+		return uint64(value), nil
+	case int64:
+		if value < 0 {
+			return 0, fmt.Errorf("invalid negative uint64: %d", value)
+		}
+		return uint64(value), nil
+	case float64:
+		if value < 0 || value != float64(uint64(value)) {
+			return 0, fmt.Errorf("invalid uint64 number: %v", value)
+		}
+		return uint64(value), nil
+	case uint64:
+		return value, nil
+	default:
+		return 0, fmt.Errorf("invalid uint64 type: %T", v)
+	}
+}