You've intentionally reduced PGP to your narrow use case. PGP/GPG will also sign and not just encrypt. If you're going to debate the subject do so honestly.

Yes, that's my point. PGP/GPG's ability to sign things is an "also", but it's the only thing it's good at. Build a version of GPG that only does signing and verification, and nobody will be tempted to use it for privacy.

Signing is an integral part of a good encryption scheme, to prevent against certain oracle attacks. The two functions are not so easily separated (if you're offering encryption).

Is the sort of signing you want to do for code signing related to the sort of signing you want to do as part of an encryption scheme?

This vaguely sounds similar to how RSA decryption/encryption and signing/verification are the same sets of operations, at the primitive level, making it easy to turn a tool that does one in to a tool that also does the other. But the actual high-level signing and encryption systems (e.g. RSA-PSS and RSA-OAEP) are not the same operations at all, and being good at one is no guarantee of being good at another.

> Is the sort of signing you want to do for code signing related to the sort of signing you want to do as part of an encryption scheme?

Same basic concept. Take a blob (compiled code or cyphertext) and a private key and sign it, so can be verified with the public key later.

https://en.wikipedia.org/wiki/Authenticated_encryption

This kind of PGP signing is also critical to the security of Linux software repos. Debian repos sign the contents of the manifest (which includes hashes of packages), and Apt repos sign individual files.

These aren't related at all! Authenticated encryption uses a symmetric MAC. Code signing is asymmetric.