re-add flag to skip unguarded app.run from CLI

src/flask/app.py

@@ -916,8 +916,8 @@ class Flask(Scaffold):
         if os.environ.get("FLASK_RUN_FROM_CLI") == "true":
             if not is_running_from_reloader():
                 click.secho(
-                    " * Ignoring a call to 'app.run()', the server is"
-                    " already being run with the 'flask run' command.\n"
+                    " * Ignoring a call to 'app.run()' that would block"
+                    " the current 'flask' CLI command.\n"
                     "   Only call 'app.run()' in an 'if __name__ =="
                     ' "__main__"\' guard.',
                     fg="red",

src/flask/cli.py

@@ -715,6 +715,11 @@ class FlaskGroup(AppGroup):
         parent: click.Context | None = None,
         **extra: t.Any,
     ) -> click.Context:
+        # Set a flag to tell app.run to become a no-op. If app.run was
+        # not in a __name__ == __main__ guard, it would start the server
+        # when importing, blocking whatever command is being called.
+        os.environ["FLASK_RUN_FROM_CLI"] = "true"
+
         # Attempt to load .env and .flask env files. The --env-file
         # option can cause another file to be loaded.
         if get_load_dotenv(self.load_dotenv):