Indeed, I can answer yes I tried the debug way and investigated the snapd source code to use it as documentation.
That just convinced me the glpi-agent is a special case strict confinement can’t cover. As I tried to explain and demonstrate here, such inventory agent was developed to be portable and as safe as possible from a past where no confinement technology was existing (the code base is more than 10 years old).
Then I think you should probably make an exception for glpi-agent and tolerate it uses classic confinement.
As a side question, in the case you will definitively deny classic confinement for glpi-agent, is it possible to use another store than snap store ?
Indeed I also just started to read that old thread about External repositories and I think the answer is no.
I’m disappointed as I think glpi-agent snap won’t finally be used if you can’t accept it is based on classic confinement. On my point of view, we still can distribute distro packages like rpm & deb for manual installation, so people won’t choose snap if it also need manual install with the “–dangerous” option.