Make --recode-samples handle exceptions, in an insanely complicated way

README.md

@@ -182,8 +182,6 @@ This also makes it run slower.
 Often it's useful to exclude events with `textual console -x EVENT`.
 
 To test file encoding, run `textual run --dev "src/textual_paint/paint.py --recode-samples"`.
-(If the program doesn't exit automatically, use `textual console -x EVENT` to check for errors.
-I'm new to asyncio in Python, and I wasn't able to get it to handle exceptions, at least not without putting a try/except inside the task, and frankly it was so obnoxiously difficult that I just had to set aside the problem for now.)
 
 If there are differences in the ANSI files, you can set up a special diff like this:
 ```bash

src/textual_paint/paint.py

@@ -3390,13 +3390,25 @@ if args.recode_samples:
                 app.file_path = file_path
             await app.save()
             print(f"Saved {filename}")
-        app.exit()
-    # asyncio.run(recode_samples())
     # have to wait for the app to be initialized
     def callback() -> None:
-        # RuntimeError: asyncio.run() cannot be called from a running event loop
-        # asyncio.run(recode_samples())
-        asyncio.create_task(recode_samples())
+        task = asyncio.create_task(recode_samples())
+        app.background_tasks.add(task)
+        def done_callback(future: asyncio.Future[None]) -> None:
+            # print("Done callback")
+            exception = future.exception()
+            # print("Done callback: exception:", repr(exception))
+            app.background_tasks.discard(task)
+            # app.exit(1 if exception else 0, exception) # nope
+            # app.exit(None, exception) # nope
+            # if exception:
+            #     raise exception # nope
+            if exception:
+                def raise_exception() -> None:
+                    raise exception
+                app.call_later(raise_exception)
+            app.exit()
+        task.add_done_callback(done_callback)
     app.call_later(callback)
 
 if args.clear_screen: