I literally quoted it in the message above:

> multi-device credentials (commonly referred to as synced passkeys).

> A backup eligible public key credential source is referred to as a multi-device credential whereas one that is not backup eligible is referred to as a single-device credential.

The previous name for single-device credentials was "resident keys".

So yes, providing a way to export and back up the Passkeys was _literally_ the intention of the WebAuthn authors from the beginning. The ability to export and sync passkeys was not a temporary accident, it has always been intended functionality.