OK but you'd still be able to use the open source "password manager" to export the keys - which solves the issue lapcat raised in this thread - even if relying

OK but you'd still be able to use the open source "password manager" to export the keys - which solves the issue lapcat raised in this thread - even if relying parties blocked it for authentication, which would be a separate issue. Someone could develop a "passkey export tool" purely for the purpose of doing credential exchange then local export. Or are you saying the credential exchange process itself could block providers?