How to call method in correct asyncio context from a different thread in Python (Textual framework)

Question

I have an old python multithreaded console app using urwid as its visualization library. I'd like to switch to Textual which looks amazing.

I've never managed a mix of multithreaded and asyncio code, and I'd like to avoid rewriting the old app to migrate all the thread-based code to async.

I'm not able to figure out how to call Textual widgets methods that update the ui from external threads.

For example, the following test code that simulates a separate thread trying to add lines to a TextLog widget raises a NoActiveAppError exception.

import time
import threading
from textual.app import App, ComposeResult
from textual.widgets import TextLog
from textual.pilot import Pilot


# simple textual app with a single textlog widget
class MyApp(App):

    def compose(self) -> ComposeResult:

        self.logbox = TextLog(id="log", wrap=True, max_lines=1024)
        yield self.logbox

# init textlog content when ready
async def on_ready(pilot: Pilot):
    pilot.app.logbox.write("Welcome to this and that!")


# separate thread
def test_thread():
    i = 0
    while True:
        # do stuff
        time.sleep(3)
        i += 1
        # this throws a NoActiveApp exception
        app.logbox.write(f"Iteration #{i}")


app = MyApp()
threading.Thread(target=test_thread).start()
app.run(auto_pilot=on_ready)

It looks like Textual is making use of contextvars, thus storing in the main async loop thread context a copy of the app instance.

For instance I'd like to call the TextLog widget write method from the separate thread, but I cannot figure out how.