feat(yjs): improve handling of external file conflicts - #3246
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Disconnect users from a yjs room if they have unsaved changes that would be overwritten by an external update. This ensures they don't lose their unsaved work and can properly save or store it somewhere, before reconnecting to the room via a page reload. Also reflect the disconnected status in the indicator.
The isStale guard only holds when the flag arrives ahead of the rewrite it announces. A peer that was offline while a recovery ran gets flag, rewrite and commit back as one merged update, so the isStale guard never fires. As a result, unsaved local changes would just be overwritten with the new content. Key the guard on a new recoveryEpoch meta value that is bumped with every isStale and never cleared. If the flag is still up the doc is untouched and the peer just leaves the room. Otherwise the rewrite has already dropped the work, so leave the room and re-seed the doc from the last reported content.
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Description
Disconnect users from a yjs room if they have unsaved changes that would be overwritten by an external update. This ensures they don't lose their unsaved work and can properly save or store it somewhere, before reconnecting to the room via a page reload.
Also reflect the disconnected status in the indicator.
The second commit tackles an edge case where a user that was offline during a recovery would lose their local work upon reconnect. See down below for explanations.
Scenarios explained
user ahas no unsaved changesuser ais in a room forfile.txtfile.txtgets external updateuser bjoins room and fetches the updated file:-> flags the room with
isStale: true-> initiates recovery
user adetects theisStalechange, stays in the roomuser ahas unsaved changesuser ais in a room forfile.txtfile.txtgets external updateuser bjoins room and fetches the updated file:-> flags the room with
isStale: true-> initiates recovery
user adetects theisStalechange and leaves the room to avoid that their changes get overwrittenuser ais not in the room anymore, hence no update for them)user ahas unsaved changes and is offline during recoveryuser ais in a room forfile.txtbut goes offlinefile.txtgets external updateuser bjoins room and fetches the updated file:-> flags the room with
isStale: true-> initiates recovery
user agoes online again-> the guard on
isStale, that would remove them from the room, never ran, meaning they stayed in the room during recovery and have the updated content now-> they now leave the room
-> they recover their content from the last known state
closes #3103