> Carbon is not trying to be 100% interoperable with C++ It's trying for some fuzzy notion of "good enough"

No, it's clearly not a "fuzzy" notion of interop even in the most uncharitable interpretation. Your assertion is mis-information.

"Seamless, bidirectional interoperability with C++, such that a library anywhere in an existing C++ stack can adopt Carbon without porting the rest."

Support mixing Carbon and C++ toolchains

Compatibility with the C++ memory model

Minimize bridge code

Unsurprising mappings between C++ and Carbon types

Allow C++ bridge code in Carbon files

Carbon inheritance from C++ types

Support use of advanced C++ features

Support basic C interoperability