Summary

• Add a dynamic Debian Docker repo fallback that uses ${VERSION_CODENAME} when available and falls back to bookworm if the repo isn’t present.
• Add a focused unit test covering the fallback logic.

Why

Debian 13 (trixie) passes OS detection, but Docker’s APT repo may not publish trixie yet. The fallback install step fails, which blocks “Validate & Install” for additional servers. This change makes Debian 13 work now and auto‑switches to trixie once Docker supports it.

Demo

https://youtu.be/FuCyfkg11Xg

Testing

• php artisan test –compact –filter=InstallDockerDebianFallbackTest
• vendor/bin/pint –dirty –format agent

/claim #8154