Query current agent metadata from inside workspace #23086

I would like to read certain information, like coder_env vars, outside the context of the coder agent (i.e. from other systemd daemons running in the workspace).

We used to do this by using gcloud instance metadata which we can easily set from terraform, however when used with prebuilds, this causes a lengthy terraform update (10-20s) if any instance metadata is changing. That's not that much faster than a non-prebuild... and probably too slow to deal with the hassle of making our template compatible with prebuilds.

Unfortunately, there are two key pieces of information that I need which change during workspace claim:

• workspace owner email. used in a ton of internal tooling.
• workspace name. Used to change the hostname of the workspace.

So, my next best idea: what if I could query the coder control plane, instead of gcloud instance metadata?

To make this work, i would need something like the workspace agent metadata API, but with the following changes:

• works with an agent token instead of a user token
• has a /me version (otherwise, i'd still be stuck, because how do I determine the UUID of the current agent?)