Squash beta testing

[spoons-and-mirrors]

The error message should be clearer

aka, which string was found multiple times? start or end?

should also probably use opencode lingo for cohesiveness (and because it works well):
Found multiple matches for oldString. Provide more surrounding lines in oldString to identify the correct match.

[Tarquinen]

yep yep good points, should copy a lot of the edit prompt as well maybe, specifically the parts about it having to be a unique string