Resetting the Syncthing index

I use Syncthing^[No, there’s no iOS client. I’m OK with that.] to keep my laptop, desktop, and workshop computers in sync.^[Why don’t I just use Dropbox like everyone else? I trust peer-to-peer syncing because I’m in control. I don’t know what Dropbox is up to.] At least 99.9% of the time it works perfectly. Rarely, it seems to choke because of some edge case that I’ve never been able to sort out.