Hi! Thanks for catching and fixing my mistake!

So that I better understand how to avoid this error in the future, is it correct that I should have just kept the history on the left side of the split?

I'm used to JOSM just handling relation modification in the background during splits: for example, if a way is part of a route relation, JOSM automatically adds the newly-created way into that relation in the correct spot when the way is split, but I guess that doesn't apply to turn restrictions.

I'll keep an eye out for similar situations in the future.  Thanks again!