I will start a thread with the cargo folks about using content based hashes... I think it's a pretty trivial change to make, it's just a perf question... Maybe it could be behind a flag...

if it’s a nontrivial change to make (somehow i doubt this) an intermediate step is at least allowing you to say “please trust that this is correctly cached”

It looks like a pretty trivial change to make - filed https://github.com/rust-lang/cargo/issues/6529 to see if they’d accept it

but that might be too much of a hook