>>> Various code seems to expect "default" to be the /last/ item in the 
>>> list returned by that function, not the first. For example, this 
>>> comment in faces.el:
>>
>> Can you perhaps clarify what you mean by "that function"?  The subject 
>> line of your bug report mentions 'font-faces', but no such function 
>> exists in Emacs.
>
> Apologies: I meant to write "face-list".
>

Thanks.  It seems the change you describe is not a recent one: the first 
element of the list returned by 'face-list' is 'default' in Emacs 27, 28, 
29 and 30.  (This is caused by e3b8ddd500, since which frame faces are 
stored in a hash table instead of an alist.)

Given this, and the fact that the docstring of 'face-list' does not 
specify the order in which the faces are returned, it's not clear to me 
that there is a bug here.  Code that assumes a given order should probably 
be fixed.