I tried using the envbuilder template without any customisation at all, providing it with a private ssh url to the gitlab repository.

I have other projects used by the same coder user (me) using private gitlab repositories that are not using the envbuilder template and they work fine.

But when envbuilder tries to clone the repository it fails with this

envbuilder v1.1.0+a3a6a83 - Build development environments from repositories in a container
#1: 📦 Cloning git@gitlab.com:bloodstock/bloodstock-app.git to /workspaces/bloodstock-app...
#1: 🔑 Using SSH authentication!
#1: 🔑 No SSH key found, falling back to agent!
#1: ❌ Failed to connect to SSH agent: error creating SSH agent: "SSH agent requested but SSH_AUTH_SOCK not-specified"
#1: Parsed Git URL as "ssh://git@gitlab.com/bloodstock/bloodstock-app.git"
Failed to clone repository: clone "git@gitlab.com:bloodstock/bloodstock-app.git": error creating SSH agent: "SSH agent requested but SSH_AUTH_SOCK not-specified"
Falling back to the default image...
No Dockerfile specified, looking for a devcontainer.json...
Failed to locate devcontainer.json: open /workspaces/bloodstock-app/.devcontainer: no such file or directory
Falling back to the default image...

At this point, i gave up and am going to use the other template, but wanted to raise it in case there was something wrong at your end. If not, feel free to close as I don't need any help. I'll try envbuilder again in 3 months or so to see if its working