More about issue #2: I've noticed that this isn't the same across all Ubuntu apps. If you click somewhere else before finalising some input in LibreOffice and in the Ubuntu system menus, your input will be erased. However, if you do the same thing in the Firefox search bar or address bar, the unfinalised input will be finalised (the same behaviour as VisualEditor has currently). I'm guessing that LibreOffice and Ubuntu are correct here, but I'm not 100% sure.

I agree fixing 1 and 2 would be great. However I think it will be difficult or maybe even impossible, because from Javascript:

1. There is no way to detect which IME is in use
2. Candidates appear in the DOM and there is no way to distinguish them from committed text
3. There is no reliable (cross-IME) event pattern that signals a commit (in particular, compositionend has no consistent meaning other than "something's happening").

One hole through which we might conceivably escape this prison is to allow browser native undo in certain circumstances. (However browser native undo can do crazy things at other times, e.g. restoring link text as blue underlined non-link text, so we'd have to be very careful).

At the moment our undo grouping is completely time based. Other editors appear to be at least partially based on wordbreaks, e.g. undo deletes words at a time. That could help with 1.

I agree that 2 sounds basically impossible with the information we get from the browser.

In T108566#1670886, @Esanders wrote:

At the moment our undo grouping is completely time based. Other editors appear to be at least partially based on wordbreaks, e.g. undo deletes words at a time. That could help with 1.

That would be good if wordbreaks were easy to define for Japanese, but unfortunately they aren't. (That's T101917.)

I agree that 2 sounds basically impossible with the information we get from the browser.

That's not such a big problem - #1 is the more important from a usability perspective. #1 is not a showstopper either, but having it fixed would definitely save users some frustration.