Fail fast when CSE is run after SelectOptimizer

common/src/main/java/dev/cel/common/values/RawProtoMessageLiteValue.java

@@ -193,14 +193,29 @@ private static Object decodeWireField(
         fieldDescriptor != null
             ? fieldDescriptor.getEncodingType() == EncodingType.LIST
             : field.defaultValue() instanceof List;
-    String protoTypeName =
-        fieldDescriptor != null
-            ? fieldDescriptor.getFieldProtoTypeName()
-            : UNKNOWN_MESSAGE_TYPE_NAME;
+    String protoTypeName = resolveProtoTypeName(field, fieldDescriptor);
 
     return decodeWireEntries(unknowns, typeCode, protoTypeName, isRepeated, converter);
   }
 
+  /**
+   * Resolves the protobuf message type name for a field.
+   *
+   * <p>Prefers the descriptor's message type name when present. Under runtime version skew (where
+   * the descriptor is omitted), falls back to the type name preserved in {@link SelectField} from
+   * the optimizer, or {@link #UNKNOWN_MESSAGE_TYPE_NAME} if unspecified.
+   */
+  private static String resolveProtoTypeName(
+      SelectField field, @Nullable FieldLiteDescriptor fieldDescriptor) {
+    if (fieldDescriptor != null) {
+      return fieldDescriptor.getFieldProtoTypeName();
+    }
+    if (!field.protoTypeName().isEmpty()) {
+      return field.protoTypeName();
+    }
+    return UNKNOWN_MESSAGE_TYPE_NAME;
+  }
+
   private static Object resolveDefault(
       SelectField field,
       @Nullable FieldLiteDescriptor fieldDescriptor,
@@ -211,7 +226,8 @@ private static Object resolveDefault(
 
     if (fieldDescriptor == null) {
       if (field.typeCode() == FieldLiteDescriptor.Type.MESSAGE.getNumber()) {
-        return create(ByteString.EMPTY, UNKNOWN_MESSAGE_TYPE_NAME, converter);
+        return create(
+            ByteString.EMPTY, resolveProtoTypeName(field, /* fieldDescriptor= */ null), converter);
       }
       throw CelAttributeNotFoundException.forFieldResolution(field.fieldName());
     }
@@ -249,6 +265,9 @@ static boolean isPresentInWire(
             ? fieldDescriptor.getProtoFieldType().getNumber()
             : field.typeCode();
 
+    // In protobuf wire format, a zero-length entry for a singular field (e.g. empty string,
+    // bytes, or empty submessage) represents explicit presence on the wire. Only packed repeated
+    // fields with empty payload represent an empty/absent collection.
     if (!isRepeated) {
       return true;
     }

common/src/main/java/dev/cel/common/values/SelectField.java

@@ -69,6 +69,12 @@ public abstract class SelectField {
    */
   public abstract @Nullable Object defaultValue();
 
+  /**
+   * Protobuf message type name of this hop (e.g. {@code "google.protobuf.Duration"}, {@code
+   * "com.example.User"}), or empty string if unknown or not a message field.
+   */
+  public abstract String protoTypeName();
+
   /**
    * Creates a presence-test qualifier hop.
    *
@@ -83,7 +89,11 @@ public static SelectField create(long fieldNumber, String fieldName) {
         fieldNumber);
     checkNotNull(fieldName);
     return new AutoValue_SelectField(
-        (int) fieldNumber, fieldName, NO_TYPE_CODE, /* defaultValue= */ null);
+        (int) fieldNumber,
+        fieldName,
+        NO_TYPE_CODE,
+        /* defaultValue= */ null,
+        /* protoTypeName= */ "");
   }
 
   /**
@@ -98,13 +108,36 @@ public static SelectField create(long fieldNumber, String fieldName) {
    */
   public static SelectField create(
       long fieldNumber, String fieldName, long typeCode, @Nullable Object defaultValue) {
+    return create(fieldNumber, fieldName, typeCode, defaultValue, /* protoTypeName= */ "");
+  }
+
+  /**
+   * Creates a fully-specified field selection hop with type code, optional default value, and
+   * protobuf type name.
+   *
+   * @param fieldNumber Protobuf field number. Takes {@code long} for compatibility with CEL's int64
+   *     constant representations.
+   * @param fieldName Protobuf field name.
+   * @param typeCode Protobuf wire type code or {@link #CEL_MAP_TYPE_CODE}. Takes {@code long} for
+   *     compatibility with CEL's int64 constant representations.
+   * @param defaultValue Default value for the field, or null if unspecified.
+   * @param protoTypeName Protobuf message type name, or empty string if unspecified.
+   */
+  public static SelectField create(
+      long fieldNumber,
+      String fieldName,
+      long typeCode,
+      @Nullable Object defaultValue,
+      String protoTypeName) {
     checkArgument(
         fieldNumber >= 1 && fieldNumber <= MAX_FIELD_NUMBER,
         "Field number out of protobuf range: %s",
         fieldNumber);
     checkNotNull(fieldName);
     checkArgument(isSupportedTypeCode(typeCode), "Invalid protobuf type code: %s", typeCode);
-    return new AutoValue_SelectField((int) fieldNumber, fieldName, (int) typeCode, defaultValue);
+    checkNotNull(protoTypeName);
+    return new AutoValue_SelectField(
+        (int) fieldNumber, fieldName, (int) typeCode, defaultValue, protoTypeName);
   }
 
   /**