"Works" in a one-off trial or with daily use? What I'm talking about is an unacceptable failure rate in the course of daily usage (by which I mean failures at least once or twice a day, sometimes considerably worse, over the course of establishing several dozen SSH connections daily)

If your OS X daily driver setup is truly stable, can you share all of the details? What OS X version? Yubikey model? GPG version? OpenSSH version?

I know at least a dozen people who have shared my experience so if there is a magic path to stabilizing it, I'm all ears.

> "Works" in a one-off trial or with daily use?

It worked with daily usage from the time I set it up (shortly after buying that particular MacBook Pro, in October 2016) until the time I quit using that machine all-day every day (c. December 2017). In addition, it worked on the previous MacBook Pro I had as well.

It still worked when I spent five minutes on it earlier today. Obviously, that's not any extensive testing but I have no reason to believe it has somehow broken itself in the time it's been sitting on a shelf, turned off.

I'll grant you that it's certainly not the easiest thing to get up and running... but I also know that it can be done and that it can work quite well. TBQH, if it had been that much of a pain in the ass, I wouldn't have bothered.

FWIW, this is a mid-/late-2016 MacBook Pro, running 10.12.something (never updated it to High Sierra), with a Yubikey Neo. GPG came from homebrew, IIRC, and SSH as shipped with the OS. I'm on mobile at the moment but I'll try to remember to go back and check all the version numbers and such later, if you're truly interested in them.

It sucks that you experienced so many issues with this but I think there's enough anecdotal evidence here to show that this can all be made to work -- and work reliably.