- Test Debian (deb.debian.org, security.debian.org), Ubuntu (archive.ubuntu.com,
security.ubuntu.com) and Alpine (dl-cdn.alpinelinux.org) repos via HTTP HEAD
- Selects target repos based on var_os and var_version from the CT script
- Warning only (not a hard fail) to support local mirrors and apt-cacher-ng setups
- Shows which repo host failed and with what HTTP status code
- Catches connectivity issues before container creation and apt-get/apk failures