I think I mostly agree, but I do have one war story of using a C++ library (Apache Avro) that parsed data and exposed a "get next std::string" method. When parsing a file, all the data was set to the last string in the file. I could see each string being returned correctly in a debugger, but once the next call to that method was made, all previous local variables were now set to the new string. Never looked too far into it but it seemed pretty clear that there was a bug in that library that was messing with the internals of std::string, (which if I understand is just a pointer to data). It was likely re-using the same data buffer to store the data for different std::string objects which shouldn't be possible (under the std::string "API contract"). It was a pain to debug because of how "private" std::string's internals are.

In other words, we can at best form API contracts in C++ that work 99% of the time.