aliasing when changing one field doesnt drop others

common/proto/table_validation.proto

@@ -2,6 +2,8 @@
 syntax = "proto3";
 package komp_ac.table_validation;
 
+import "google/protobuf/field_mask.proto";
+
 // This proto is the canonical server-side storage and distribution contract for
 // client validation configuration.
 //
@@ -189,6 +191,11 @@ message UpdateFieldValidationRequest {
   string tableName = 2;
   string dataKey = 3;
   FieldValidation validation = 4;
+
+  // Omitted keeps the legacy full-replacement behavior. Otherwise, only the
+  // selected FieldValidation properties are changed; selecting an absent
+  // message property deliberately removes it.
+  google.protobuf.FieldMask update_mask = 5;
 }
 
 message UpdateFieldValidationResponse {