What is "spinal-tap grade" security? As stated here Ed448 is different from Ed25519 because of "spinal-tap grade" security. What does this mean?
It is security on a 0-10 scale that goes to 11.

The cost of cryptanalysis to break a cryptosystem with a 128-bit security level, like Ed25519, is out of reach for humanity already.  A higher security level like Ed448's doesn't have any actual meaning with current understanding of cryptanalytic attacks.  The only purpose it serves is to hedge against potential modest future advances in cryptanalysis—a radical advance like a cheap quantum computer would devastate Ed25519 and Ed448 alike, of course.

P.S.  I see you tagged this jwt and jwe.  JWT and JWE, and JOSE generally, provide a different sense of ‘spinal-tap grade’ security, which is that they are a parody of security.