fix(install): docker install failure when containerd.io candidate is missing from Docker repo

[BenderV]

note: generated by AI, but solved my issue.

Root issue

On Debian/Ubuntu systems, the installer occasionally fails during Docker installation with a 404 Not Found error when fetching containerd.io.

This happens when:

• apt resolves a newer containerd.io version from Docker's repository metadata
• but the corresponding .deb file is not yet available (or temporarily missing) on the Docker CDN

In that state, repeated apt-get install containerd.io attempts always fail, even though older, valid versions are still available in the same repository.

This is a known class of issue during Docker repo syncs and CDN propagation delays.

---

Proposed fix

Make Docker installation resilient to missing containerd.io artifacts by adding a fallback strategy:

1. Attempt the normal Docker install using apt (unchanged behavior in the healthy case)

2. If it fails:

   • Refresh apt metadata
   • Enumerate all available containerd.io versions via apt-cache madison
   • Retry installation by explicitly pinning each available version (newest → oldest)

3. Succeed as soon as a valid version is found

This ensures:

• No behavior change when the Docker repo is consistent
• Automatic recovery when a candidate version exists in metadata but the .deb is unavailable
• Fully non-interactive, production-safe installs

---

Why this approach

• Avoids hard-coding a specific containerd version
• Works across Debian and Ubuntu
• Handles transient Docker repo/CDN inconsistencies gracefully
• Keeps the installer self-healing without user intervention

---

User impact

• Fixes intermittent install failures on fresh Debian/Ubuntu systems
• Eliminates confusing 404 Not Found errors during Docker setup
• Improves reliability of unattended installs