> My understanding is that Wagner's thesis is mostly concerned with "history-sensitive" error recovery in an IDE: using earlier syntax trees as an additional input to the error recovery process in order to better understand the user's intent when editing.

That matches my understanding (note that Wagner's error recovery algorithm is probably best supplemented with Lukas Diekmann's thesis, which corrects and expands it a bit https://diekmann.co.uk/diekmann_phd.pdf).

Because Wagner's algorithm relies on history and context, it does sometimes do some unexpected (and not always useful things). However, I don't see any fundamental reason why it couldn't be paired with a "traditional" error recovery approach (I have one to sell!) to try and get the best of both worlds.