> I must still be missing something. "Models extend outside the image", true. But leaking implementation detail into the external model is just bad design. And the hash of an object is very much an implementation detail, IMHO.

I wouldn't call it bad design -- but I do agree hashes are a bit more
dicey as we see someone just discovering a DateAndTime hash
improvement.  Great!

However, hash improvements are generally few and far between, with a
little care the rewards of higher transparency can still be had.  Like
ReferenceStream, Magma "solves" it by rehashing standard Dictionary's
on materialization, but some of the special hashed collections types
this is either not supported or is impractical.