Clarify query failure docstring a bit (#504)

temporal/api/workflowservice/v1/request_response.proto

@@ -918,16 +918,18 @@ message RespondQueryTaskCompletedRequest {
     // Mutually exclusive with `error_message` and `failure`. Set when the query succeeds.
     temporal.api.common.v1.Payloads query_result = 3;
     // A plain error message that must be set if completed_type is QUERY_RESULT_TYPE_FAILED.
-    // SDKs should also fill in the more complete `failure` field to provide the full context and support encryption of
-    // the failure message.
-    // The error message will be duplicated if the `failure` field is present to support callers that pre-date the
-    // addition of that field.
+    // SDKs should also fill in the more complete `failure` field to provide the full context and
+    // support encryption of failure information.
+    // `error_message` will be duplicated if the `failure` field is present to support callers
+    // that pre-date the addition of that field, regardless of whether or not a custom failure
+    // converter is used.
     // Mutually exclusive with `query_result`. Set when the query fails.
     string error_message = 4;
     reserved 5;
     string namespace = 6;
-    // The full reason for this query failure. This field is newer than `error_message` and can be encoded by the SDK's
-    // failure converter to support E2E encryption of messages and stack traces.
+    // The full reason for this query failure. This field is newer than `error_message` and can be
+    // encoded by the SDK's failure converter to support E2E encryption of messages and stack
+    // traces.
     // Mutually exclusive with `query_result`. Set when the query fails.
     temporal.api.failure.v1.Failure failure = 7;
 }