The underlying APIs don't allow e.g. copying depth32float-stencil8's depth aspect into depth32float. In native, you can just copy with an intermediate buffer. But in WebGPU that's impossible: copies from buffer into depth32float aren't allowed because we can't validate the depth range (unless a future unrestricted-depth feature is enabled).

We could make such copies possible by implementing them with an internal intermediate buffer.

Originally posted by @kainino0x in #2322 (comment)