tor-spec: We should specify how clients pick between different handshake types
As far as I can tell we do currently not specify how a client should pick between TAP or NTor handshakes in tor-spec.txt.
We do specify under TAP that the handshake should not be used because it is slow and weak, but we do not specify anywhere how a client should pick among the set of handshakes.
This is currently not a big issue because we only have two handshake types and Ntor is much preferred over TAP, but in a future where we might have different more fancy handshakes (PQ?) then it might be good to specify the order of which clients should prefer a given handshake over another.