"[T]his means that mutating a key in a hash table based on eq-comparator or eqv-comparator, or the equality predicates eq? or eqv?, may be possible, but mutating a key in a hash table based on equal-comparator or equal? is almost always unsafe."

Initially I thought it would be trivial to replace them with "comparator returned by make-eq-comparator" and such, but I realized it's more complicated.

Srfi-128's make-eq-comparator and make-eqv-comparator are specified to use the same hash function (default-hash) as make-equal-comparator.  That means the hash function is mostly likely to recurse into lists and vectors, so mutating the key of hashtables based on the comparators returned by make-eq-comparator / make-eqv-comparator can be said unsafe, too.

I actually overlooked that during srfi-128 discussion.  Was there a reason for make-eq[v]-comparator using default-hash?  It might be inefficient if I only want to hash with object identity for eq-hashtable.