Update cancellation documentation in operations.proto

google/longrunning/operations.proto

@@ -58,7 +58,10 @@ service Operations {
   // `google.rpc.Code.UNIMPLEMENTED`.  Clients can use
   // [Operations.GetOperation][google.longrunning.Operations.GetOperation] or
   // other methods to check whether the cancellation succeeded or whether the
-  // operation completed despite cancellation.
+  // operation completed despite cancellation. On successful cancellation,
+  // the operation is not deleted; instead, it becomes an operation with
+  // an [Operation.error][google.longrunning.Operation.error] value with a [google.rpc.Status.code][google.rpc.Status.code] of 1,
+  // corresponding to `Code.CANCELLED`.
   rpc CancelOperation(CancelOperationRequest) returns (google.protobuf.Empty) {
     option (google.api.http) = { post: "/v1/{name=operations/**}:cancel" body: "*" };
   }
@@ -95,7 +98,7 @@ message Operation {
   // If `done` == `false`, neither `error` nor `response` is set.
   // If `done` == `true`, exactly one of `error` or `response` is set.
   oneof result {
-    // The error result of the operation in case of failure.
+    // The error result of the operation in case of failure or cancellation.
     google.rpc.Status error = 4;
 
     // The normal response of the operation in case of success.  If the original