Cleanup document table entries and y.js state file handling

[juliusknorr]

From our discussion:

Current state

close

• delete session table entry
• delete inactive sessions (without steps)
• document is kept
• yjs file is kept
• steps are kept

cron cleanup

• foreach document without sessions and unsaved changes

  • reset document
    • delete all steps
    • delete all sessions
    • delete document
    • keep y.js file

• delete inactive sessions (without steps) -> can trigger document cleanup in the next cron run

• sessions with steps and the document are kept

Goal: support both keeping and removing y.js file

• do not drop document db entry, only if y.js file is also removed (Julius)
• ensure reconnects can detect an underlying y.js file has been recreated
  • backend: write unique id on insert to oc_text_documents for the base_version_etag (Julius)
  • frontend: on reconnect compare client base_version_etag with server one, full editor restart if no match (Max)
• drop y.js state only on external file writes if no sessions are active (Jonas)
  • this will ensure we don't have a conflict dialog
• check node deletion event for cleanup (follow up)

[mejo-]

Scenarios (to be complemented):

• Session got removed in backend but document+yjs stayed (baseVersionEtag still the same) -> Frontend reconnect sufficient
• Sessions and document+yjs got removed in backend: -> Frontend needs a full reset (page reload) to load new yjs state

[mejo-]

This is all done now. The relevant PRs to be backported are:

• Reset document session on filesystem change #5481
• fix: catch expected exception in event handler #5497
• Ensure document stays consistent with y.js state file #5477
• fix(sync): If baseVersionEtag changed, reset frontend #5523

[mejo-]

stable28 backport: #5541