[Bug]: EW stage pages don't load correctly

[ioanarusiczki]

What happened?

While looking over mozilla/addons-server#23260 (comment)

From -dev or -stage https://extensionworkshop.allizom.org/ is not loading content

What did you expect to happen?

Looking in the Console there's lots of CSP errors

This is only reproducible from -dev/stage
Prod is fine

[diox]

Summary of discussion on slack:

HTML files were uploaded with the wrong CSP and caching headers. This not only breaks the site, but poisons the cache as well, because we set cache-control: max-age=31536000, immutable on those files. If that were to happen in prod, that would be terrible, impossible to recover from without asking every visitor to hard-refresh once the problem is fixed.

HTML files were uploaded by this deploy script:

extension-workshop/.utils/gcs-deploy.sh

Line 83 in ca434f1

# evertying else in bucket.

The workflow that lead to this is https://github.com/mozilla/extension-workshop/actions/runs/14238009866/job/39901250602

We can see that html files are rsynced with the right headers... and then overwritten by the "catch-all" last rsync, which is not supposed to happen. Under normal, working circumstances, the only thing that prevents that from happening is the fact that rsync shouldn't overwrite files that haven't changed, but this is super fragile, and this issue is the proof that it can fail.

We should add some exclusions to the last rsync step in that deploy script to ensure it doesn't accidentally overwrites .html, .svg and .js files that it should already have uploaded during previous steps.

[diox]

One suspicion I have is that it's more likely to happen when we do several deploys (commits) in quick succession. Which is more likely to happen on dev. On top of fixing the deploy, we should prevent concurrent deploy in GitHub Actions.