Vlad as stated, I have things configured properly and it had been working for months.
I went and toggled the extension in safari (disabled then reenabled) and now it’s working again with no other changes in the system, browser, or kagi settings. I did go select another search provider in kagi settings and then reselect yahoo for good measure too, though, so unfortunately can’t pin it down beyond those two toggle actions. But I had also previously re-selected yahoo already prior to posting so I think it is likely the extension toggle that made things work.