[cderv]

On ubuntu runners, apt installs in the smoke tests sometimes crawl on a degraded azure.archive.ubuntu.com node. In this job from #15186, Set up R took 20 minutes and Install Playwright system dependencies failed at its 15 minute limit.

Root cause

The degraded node serves package indexes at full speed but archives at tens of kB/s. The runner images set Acquire::Retries 1 and Acquire::http::Timeout 15, which only catch a total stall, so apt never moves to archive.ubuntu.com, the next entry in /etc/apt/apt-mirrors.txt. This is actions/runner-images#14823, still open (a fix is proposed in actions/runner-images#14596).

Fix

The Azure line is dropped from apt-mirrors.txt only when the mirror is measured slow, so healthy runs keep using it and the load does not move to Canonical's servers.

• Before setup-r, whose apt calls can't be wrapped, a new step downloads one multi-megabyte .deb from the Azure mirror with curl --speed-limit, and drops the mirror if the speed stays under 1 MB/s for 10 seconds.
• The same step writes a small helper, $APT_WITH_FALLBACK, used by the Playwright deps step and the two apt-get steps. Each attempt gets 3 minutes (healthy runs take 20 to 45 seconds). After a failed attempt, the mirror is dropped, dpkg --configure -a finishes an install the timeout interrupted, and the command is retried.

Both checks are needed: the speed sample is one point in time, and a node can start fast and slow down in the middle of a download.

The logic is inline in test-smokes.yml rather than a local composite action, because release mode in test-smokes-built.yml checks out older tags that would not contain the action directory.

Testing

Tested with throwaway probe workflows on a fork, running the step text from test-smokes.yml:

• The degraded node showed up live in some runs. Attempts were killed at 3 minutes and the retry finished in about 50 seconds on archive.ubuntu.com.
• With traffic from the Azure mirror throttled to 50 kB/s, the speed check dropped it and setup-r downloaded everything from archive.ubuntu.com.
• Healthy runs kept using the Azure mirror.

The dpkg --configure -a recovery was not exercised, as the probes only killed attempts during the download.

Checklist

I have (if applicable):

• referenced the GitHub issue this PR closes
• updated the appropriate changelog in the PR
• ensured the present test suite passes
• added new tests
• created a separate documentation PR in Quarto's website repo and linked it to this PR

AI-assisted PR

• AI tool used: Claude Code
• Codebase grounding: local clone, actions/runner-images source via GitHub CLI
• Human review: I have reviewed, tested, and verified the AI-generated content before submitting.

Note: autonomous AI agents submitting PRs without human oversight are not permitted — see the Code of Conduct.

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