Situation:
We recently created a report (copy of report 206 "Sales - Invoice") to change the layout according to the customers wishes. We copied the standard rdlc-Layout and dataset in our VS-Code project and modified it to our needs. We opened Visual Studio to edit the layout and saved the new rdlc-Layout back to our project folder.
The app compiled without error and was also possible to be published to the server. Just only when we try to execute our report we got us a cryptic error message which was the result of a syntax error and missing fields in the dataset.

Question:
Is there a possibility to open the report designer from VS-Code like it was from the old dev-environment and to get error messages like syntax errors or mising fields in the dataset during creation of the app-package ?
What is the best way to make/edit a rdlc-report layout ?

Answer: By design, Dataset and layout development are now disconnected, considering what was it with CSIDE.
What partner does is correct and they just need more strict tests as part of their own extension development lifecycle.
If they would like to introduce a deeper validation of the RDLC context from within the compilation (this would also impact performance and overall extension compilation). We would like to request this to change.