castle

Agent Castle — NixOS foundation for self-hosted infrastructure where humans and their agents work together.

Castle is a library of NixOS modules and tooling: declarative, opinionated, encrypted end to end. Point it at some Linux boxes — a Hetzner VM, a machine under your desk, a datacenter in your basement — and out comes a working environment for the mixed human/agent workflow.

Why

The substrate for humans working alongside agents doesn't really exist yet. Team chat wasn't designed for it, cloud IDEs assume one human per seat, docker-on-laptop is not a place for agents to actually live. Teams end up gluing SaaS accounts together, scattering conversation history across random tools, and hoping nobody's laptop dies with a session inside it.

Castle takes the position that this substrate should be:

• Yours. Self-hosted, encrypted disks, no third party sitting in the middle of your agent conversations.
• Nix-first. Every host, user, service, and secret declared in one repo. Rebuilds are reproducible. Rollback is a git revert.
• Small. Not fleet management. A handful of nodes, arranged however fits.
• Opinionated. Sensible defaults, one blessed way to do each thing. Cloudflare Origin CA over ACME. sops-nix over Vault. ZFS over tin foil.

What you get

A library of NixOS modules for the pieces you need:

• Long-form discussion — Discourse behind Caddy, private by default (no guest reads, invite-only signup, admin-approved accounts).
• Code hosting — Forgejo with declaratively provisioned accounts.
• A user registry — castle.users.<name> declares people once; every service reads the same list.
• Encrypted disks — ZFS with per-host passphrase, entered remotely over SSH into the initrd.
• One-shot provisioning — install-host <name> generates keys, plants secrets, and kexecs a NixOS installer over any live Linux.
• Declarative deploys — deploy .#<name> with automatic rollback.

Arrange the pieces however you want. Everything on one node. One node per service. A dedicated node for each person's agents. Castle is a toolkit; the topology is yours.

More services (issue tracking, chat, dashboards, agent-facing APIs) land as they're needed.

Design tenets

• Data-only host declarations. Each host is one entry in hosts.nix, tuned through castle.* options. Nothing per-host is hardcoded in the library.
• One source of truth for users. castle.users.<name> propagates to every service that has accounts.
• Encrypted by default. No unencrypted disks in the fleet.
• No ACME. Cloudflare Origin CA, fifteen-year cert, one rotation on your calendar instead of one per certificate.
• No forking. Consume as a flake input, tune via options, add your own modules alongside.

Getting started

mkdir my-castle && cd my-castle
nix flake init -t github:reflection-dev/castle

Everything about operating your castle — Cloudflare setup, sops recipients, adding a host, deploying — lives in the README that gets copied into your instance.

Reference

Technical reference for the library — flake outputs, module options, repo layout — lives in docs/reference.md.