Subpath with reverse proxy yields failed to load application

[courtland]

What happened:
I have grafana and image renderer running in separate podman containers on the host network. Grafana is behind a Traefik reverse proxy and accessed via a subpath (https://fqdn/lgtm/). When I click Generate image, the resulting image is a capture of the "grafana failed to load..." screen. The request to image-renderer is successful and contains the right URL to render, but it seems that chromium is trying to download assets without the subpath. If I load the render URL in a browser the graph loads and the asset paths are correct. It's almost as if chromium is ignoring the <base href="...>. I get the same result when hitting the url via curl on the same host.

I've tried just about every combination of serve_from_sub_path, root_url, domain, server_url, and callback_url. If I explicitly set callback_url to "f"http://localhost:port" it times out on what I believe is a redirect to login page. Similar result with curl on localhost.

What you expected to happen:

Render the correct graph

How to reproduce it (as minimally and precisely as possible):

See attached logs and configs

grafana-config.txt
image-config.txt
logs.txt

Environment:

• Grafana Image Renderer version: 4.0.14
• Grafana version: 12.1.0
• Installed plugin or remote renderer service: image-renderer via localhost
• OS Grafana Image Renderer is installed on: official docker container
• User OS & Browser: Chrome 138.0.7204.184 MacOS 14.6.1

Possibly related to #509? I've looked into every other resolved issue that seems to be similar.

Thank you.