test: detect out of sync state and recovery via yjs pendingStructs

[mejo-]

🏁 Checklist

• Code is properly formatted (npm run lint / npm run stylelint / composer run cs:check)
• Sign-off message is added to all commits
• Tests (unit, integration and/or end-to-end) passing and the changes are covered with tests

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 59.58%. Comparing base (69065e5) to head (ca30ea1).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7700      +/-   ##
==========================================
+ Coverage   59.56%   59.58%   +0.01%     
==========================================
  Files         502      503       +1     
  Lines       39067    39080      +13     
  Branches     1129     1130       +1     
==========================================
+ Hits        23270    23285      +15     
+ Misses      15689    15687       -2     
  Partials      108      108              

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