I was vaguely flippant in my post and it lacked nuance. Actually this project [and my workplace in general] is very friendly and collegial, he was happy to do it, he even already knew where to look since I had done the bisect and otherwise triaged the rest of the issue. We collaborated on an even larger-scale refactoring earlier this year.

Mainly my point was the first paragraph; that bisect is awesome right up until the issue is in a ten thousand line commit.