Don't mention MultiOperation in Update-with-Start error (#7826)

## What changed?

Always say "Update-with-Start" in the error message returned to the user
when using MultiOperations.

(internally, History will still use MultiOperation in the error
messages)

## Why?

Users wouldn't (and shouldn't) know that Update-with-Start happens to be
a MultiOperation.

## How did you test it?
- [ ] built
- [ ] run locally and tested manually
- [x] covered by existing tests
- [ ] added new unit test(s)
- [ ] added new functional test(s)

## Potential risks

I don't expect any users to match on that string. There might be SDK
tests that break now; I'll have to follow up on that.

Author: stephanos

service/frontend/workflow_handler.go

@@ -545,9 +545,9 @@ func (wh *WorkflowHandler) ExecuteMultiOperation(
 	if err != nil {
 		var multiErr *serviceerror.MultiOperationExecution
 		if errors.As(err, &multiErr) {
-			// Trim error message for end-users.
+			// Tweak error message for end-users to match the feature name.
 			// The per-operation errors are embedded inside the error and unpacked by the SDK.
-			multiErr.Message = "MultiOperation could not be executed."
+			multiErr.Message = "Update-with-Start could not be executed."
 		}
 		return nil, err
 	}
@@ -590,7 +590,7 @@ func (wh *WorkflowHandler) convertToHistoryMultiOperationRequest(
 	}
 
 	if hasError {
-		return nil, serviceerror.NewMultiOperationExecution("MultiOperation could not be executed.", errs)
+		return nil, serviceerror.NewMultiOperationExecution("Update-with-Start could not be executed.", errs)
 	}
 
 	return &historyservice.ExecuteMultiOperationRequest{

service/frontend/workflow_handler_test.go

@@ -3401,7 +3401,7 @@ func (s *WorkflowHandlerSuite) TestExecuteMultiOperation() {
 	})
 
 	assertMultiOpsErr := func(expectedErrs []error, actual error) {
-		s.Equal("MultiOperation could not be executed.", actual.Error())
+		s.Equal("Update-with-Start could not be executed.", actual.Error())
 		s.EqualValues(expectedErrs, actual.(*serviceerror.MultiOperationExecution).OperationErrors())
 	}
 

tests/update_workflow_test.go

@@ -5309,7 +5309,7 @@ func (s *UpdateWorkflowSuite) TestUpdateWithStart() {
 			uwsCh := sendUpdateWithStart(testcore.NewContext(), startReq, updateReq)
 			uwsRes := <-uwsCh
 			s.Error(uwsRes.err)
-			s.Equal("MultiOperation could not be executed.", uwsRes.err.Error())
+			s.Equal("Update-with-Start could not be executed.", uwsRes.err.Error())
 			errs := uwsRes.err.(*serviceerror.MultiOperationExecution).OperationErrors()
 			s.Len(errs, 2)
 			var alreadyStartedErr *serviceerror.WorkflowExecutionAlreadyStarted
@@ -5488,7 +5488,7 @@ func (s *UpdateWorkflowSuite) TestUpdateWithStart() {
 
 			uwsRes := <-uwsCh
 			s.Error(uwsRes.err)
-			s.Equal("MultiOperation could not be executed.", uwsRes.err.Error())
+			s.Equal("Update-with-Start could not be executed.", uwsRes.err.Error())
 			errs := uwsRes.err.(*serviceerror.MultiOperationExecution).OperationErrors()
 			s.Len(errs, 2)
 			s.Contains(errs[0].Error(), "Workflow execution already finished")