[ihavespoons]

The change

• sibyl.nft includes /etc/nftables/sibyl.d/*.nft in its input chain. An administrator opens a port that a container publishes with one rule file there, such as tcp dport 9000 accept.
• The image ships only a README in sibyl.d. A local rule file therefore does not stop bootc from updating sibyl.nft.
• nftables.service starts with /usr/libexec/sibyl/nft-load. If the rules fail to load at boot, the script loads sibyl.nft without the drop-ins, so a bad file cannot leave the host with no firewall.
• The reload runs nft -f /etc/sysconfig/nftables.conf. The stock reload flushes the whole ruleset, which also drops the rules of other programs such as tailscaled. sibyl.nft starts with destroy table, so the new reload replaces only the sibyl table.
• The host guide, the troubleshooting guide, the design overview and AGENTS.md describe the directory.

Verification

With nftables in a fedora:44 container:

• An empty sibyl.d loads, because a glob include that matches no file is not an error.
• Two rule files load into the input chain. A second load gives the same 2 rules, not 4.
• A reload with a bad file fails, and the old rules stay.
• At boot with a bad file, nft-load logs the error and loads the base rules with policy drop and SSH. If the base file is broken too, it exits 1.

The arm64 host image builds. It has the script and the unit drop-in, and bootc container lint passes 14 checks. shellcheck passes.

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