def on_serve(
        self, server: LiveReloadServer, /, *, config: MkDocsConfig, builder: Callable
    ) -> LiveReloadServer | None:
        """
        The `serve` event is only called when the `serve` command is used during
        development. It runs only once, after the first build finishes.
        It is passed the `Server` instance which can be modified before
        it is activated. For example, additional files or directories could be added
        to the list of "watched" files for auto-reloading.

        Args:
            server: `livereload.Server` instance
            config: global configuration object
            builder: a callable which gets passed to each call to `server.watch`

        Returns:
            `livereload.Server` instance
        """
        return server

        The `serve` event is only called when the `serve` command is used during
        development. It runs only once, after the first build finishes.
        It is passed the `Server` instance which can be modified before
        it is activated. For example, additional files or directories could be added
        to the list of "watched" files for auto-reloading.

        Args:
            server: `livereload.Server` instance
            config: global configuration object
            builder: a callable which gets passed to each call to `server.watch`

        Returns:
            `livereload.Server` instance
        
mkdocs/plugins.py