ci: make tmux install resilient to third-party apt repo flakiness

[pbean]

Problem

The recurring "flaky" CI failure (most recently the #17 / 0.7.4 merge run, job test (py3.12), exit 100) is not a flaky pytest test — it's the Install tmux step.

The step ran sudo apt-get update && sudo apt-get install -y tmux under a -e shell. The job log shows apt-get update failing with a Hash Sum mismatch on https://dl.google.com/linux/chrome-stable/deb — a third-party repo baked into the GitHub runner image, unrelated to this project (the CDN served a stale index mid-publish). The Ubuntu archive lists fetched fine; only Chrome's Packages.gz failed its hash check. Because update is chained with &&, that unrelated hiccup returned non-zero and killed the whole job. It's intermittent (other matrix legs passed in the same run), which is exactly why it keeps recurring.

Fix

• apt-get update ... || true — unrelated third-party repo flakiness can no longer fail the build (the Ubuntu lists still refresh, so tmux installs cleanly).
• tmux -V — safety net: if the swallowed update error ever did prevent install, the job fails on a clear, on-topic line instead of silently skipping the ~27 generic_tmux integration tests.
• Acquire::Retries=3 — cheap resilience for genuine transient blips on the Ubuntu archive.

tmux is not pre-installed on ubuntu-24.04, so dropping the step was rejected (it would silently drop integration-test coverage).

🤖 Generated with Claude Code

Summary by CodeRabbit

• Chores
  • Improved the CI test setup to handle package installation more reliably.
  • The workflow now retries package index updates and continues safely when a temporary repository issue occurs.
  • Verification still ensures the required tool is actually installed before tests proceed.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 09546c60-57dd-4f61-a9ae-a3f18bedd08a

📥 Commits

Reviewing files that changed from the base of the PR and between df5418e and 4a3b7a3.

📒 Files selected for processing (1)

• .github/workflows/ci.yml

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Walkthrough

The CI test job now installs tmux with retry-tolerant apt-get update handling, then verifies the installed binary with tmux -V.

Changes

CI tmux install step

Layer / File(s)	Summary
Install tmux step .github/workflows/ci.yml	The test job’s tmux install step now retries apt-get update, tolerates update failures, installs tmux, and checks the installed version.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

A tiny rabbit hops through CI,
With tmux tucked in snugly nearby.
🐇 apt-get may grumble,
But version checks rumble,
And builds keep on leaping high.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the CI change to harden tmux installation against flaky third-party APT repo failures.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/ci-tmux-apt-resilient

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