gpg-ssh signing with AgentForwarding

Hello Git community, Not sure what search terms I haven't used, but I'll try to describe the use-case

On my local machine I have a SSH key, and I use AgentForwarding when I go out and about to other hosts (dev machines) The usual workflow of using the forwarded socket works for pull and push.

Where it gets pitch-dark is when I try to use my ssh key to sign git commits.
Following is my git config on the remote host:
=====================
[user]
    name = John Doe
    email = jdoe@jdoe.com
# on my local machine(gpg-ssh signing works): signingkey =
/Users/jdoe/.ssh/id_ecdsa.pub
    signingkey = WHAT_SHOULD_I_PUT_HERE # on my laptop its the path to
the public key from Secretive, or just omit it?
[gpg]
    format = ssh
[commit]
    gpgsign = true
[gpg "ssh"]
    allowedSignersFile = /Users/jdoe/.gpg.ssh.allowedSignersFile #
contents is: "email1,email2 key-type public_key comment"
=====================

I've tried
1. `ssh-agent -a /path/to/ssh.sock` - errored with address already in use
2. signingkey set to a path on the remote host with my public key,
errored with "no private key found"

I sense that I should be able to employ `gpg.ssh.defaultKeyCommand` to use the socket somehow, but I can't wrap my head around it or find some docs/guidance.

Other (related) links
https://developer.1password.com/docs/ssh/git-commit-signing/ - I think
that 1Password invested the time to make it work
https://github.com/maxgoedjen/secretive/discussions/338#discussioncomment-11170722
- asked the same on Secretive repo, which is one way to store keys
https://github.com/maxgoedjen/secretive/issues/405#issuecomment-2460948732
- also here.

Thank you, Jordan