Steps to reproduce

1. Try to revert a Wikibase edit.

Actual result

2. Notice that the summary is limited to 200 characters.
3. Use the browser developer tools to lift the limit/make it larger.
4. Add a summary longer than 200 characters and save it.
5. Notice that the longer summary was saved in its entirety, the backend didn’t reject or truncate it. (Example edit: the summary is 202 characters long.)

Expected result

2. Notice that the summary is limited to as many characters that can actually be saved (if there’s a such limit at all).

Additional information

Summary length limit was increased in T6714 (although it was 255 bytes even before, not only 200), maybe Wikibase was forgot there?