This doesn't seem to be related to focusable nodes or the end of the document. All you need to do is put the cursor in a block slug after a references list.

Suppose the references list is at (23,25). What happens is this:

• setSelection (25,25) is called
• It tries to compute insertion annotations by pulling from the left
• It does so by calling getNearestContentOffset( 24, -1 )
• Two stack levels deeper, getRelativeOffset() notices that 24 is inside of a handlesOwnChildren node and throws an exception

Questions:

• Why is reference list a handlesOwnChildren node? Is it because <ref> can be nested inside of <references>?
• Why do we do offset-1 here? There is a Math.max() to guard against ending up at -1, but this bug uncovers another reason why subtracting one from an offset is dangerous and should ideally never be done

Change 155260 had a related patch set uploaded by Esanders:
Fix check for left/right annotations

https://gerrit.wikimedia.org/r/155260

Change 155260 merged by jenkins-bot:
Fix check for left/right annotations

https://gerrit.wikimedia.org/r/155260