Extension Entry Point: JupyterLab 4.0 Transition from Server Extensions to Application Extensions

Goal: Determine whether JupyterLab 4.0 allows an extension to declare both the legacy `jupyter_server_extension` entry point and the new `jupyter_server.extension` entry point simultaneously during the migration from the Server Extension system to the Application Extension system. Constraints: The release notes state that legacy server extensions will be deprecated in a future major release, but the documentation does not specify a migration path or confirm if dual entry points are accepted, rejected, or cause conflicts. No automated migration tool exists, so developers must manually test extensions in a JupyterLab 4.0 environment to observe loading behavior.

Questions:

• Will JupyterLab 4.0 load an extension that provides both entry points, and if so, which one takes precedence?
• What runtime behavior or warnings should developers expect when dual entry points are present?
• Are there any version constraints or compatibility flags that control this behavior?