Out of band changes are not detected

[3coins]

Related to PR #83

There are no definitive steps to reproduce, but in certain scenarios notebook stops tracking out of band updates to the file. Once this happens, re-opening the notebook or refreshing the browser doesn't update the content, and any out of band updates are still not tracked. A side effect of this is that after restarting the server, all out of band updates are lost, when notebook is re-opened.

I used combination of scripted and manual out of band updates to the text file. Here is the script used.

#!/bin/bash
# Sets the content `untitled.txt`, triggering an out-of-band change. This
# happens after 5 seconds.

filename="../playground/oob-test.txt"
n=10
   for i in $(seq 1 "$n"); do
    echo "Triggering out-of-band change in 5 seconds..."
    sleep 1
    echo "Out of band change $i" > "$filename"
   done

echo "Done making out of band changes to '$filename'."

[dlqqq]

@3coins I was able to consistently reproduce this issue on PR #83, but in a very different way. I wanted to optimize the logic to not save immediately after opening the YDoc. I added this check in YRoom._on_jupyter_ydoc_update():

# TODO: Why does this stop OOB changes from working?
if self.file_api._ydoc_content_loading:
    self.log.error("SKIPPING SAVE!!!!")
    return

This seemed to reproduce the bug you're reporting here, since I observed that:

• The file was no longer being read from disk
• The JupyterLab file had a different content from the file on disk
• Out-of-band changes were no longer being detected

I added some logging to the YRoomFileAPI._watch_file() loop to see what was going on. Turns out an exception was being silently raised, halting the loop. By adding another except Exception as e: ... check, I was able to see the error causing this bug in the console:

[E 2025-05-29 08:43:04.811 ServerDocsApp] Exception occurred in `_watch_file() background task for YRoom 'text:file:3b92ad47-abb4-4cef-8360-e6c61ae43809'.
    Traceback (most recent call last):
      File "/Users/dlq/workplace/jupyter-server-documents/jupyter_server_documents/rooms/yroom_file_api.py", line 172, in _watch_file
        if self._save_scheduled:
           ^^^^^^^^^^^^^^^^^^^^
    AttributeError: 'YRoomFileAPI' object has no attribute '_save_scheduled'

Turns out this may have just been caused by forgetting to initialize an attribute in the constructor. 😅