Fold all newly loaded files and all files loaded from the session file at Sublime startup

folding_listener.py

import sublime
import sublime_plugin

def fold(view):
    view.run_command("fold_by_level", {"level": 2})

def plugin_loaded():
    for window in sublime.windows():
        for view in window.views():
            fold(view)

class FoldingEventListener(sublime_plugin.EventListener):
    def on_load_async(self, view):
        fold(view)