gatezh

You're right, thanks. The trailing ssh: is the comment: changing or removing it leaves the fingerprint the same. The FIDO application ID is also encoded inside the key blob, and it's also "ssh:", which is what confused me. I'll fix the post.

Author here. Thanks to js2 for posting this, and to everyone for the comments. I've learned a lot from this thread.

To answer the question a few people asked: I ended up using Secretive. The native approach works, but I couldn't live with the Touch ID prompt it shows. Secretive keeps the keys in the Secure Enclave too, with a much better prompt and per-key settings. I'm writing a part 2 about it, including forwarding the agent into a dev container so the key never enters the container.