The default edit summaries are not capitalised. Here, for example:
I've not screenshot all the other default summaries that I am aware of, but none (apart from the final one, below) are similarly not capitalised:
added n characters in body
deleted n characters in body
rolled back to previous question
Oddly though, this one is in title case:
- Rollback to Revision n
Athough edit summaries are not expressly referred to in the "Use sentence casing" section of the style guide, by my reading of it they should be capitalised for consistency across the network.
Or have I missed something?
1I've not been able to locate a duplicate specifically on this topic, but do note the final bullet point of this apparently unresolved feature request from just under 10 years' ago that refers to using sentence case in the edit-comment field.