nixfiles/AGENTS.md

AGENTS.md

This file provides guidance to coding agents when working with code in this repository.

CLAUDE.md at the repo root is a symlink to this file — edit AGENTS.md, not the symlink (some tools refuse to write through a symlink and will error on CLAUDE.md).

Prefer this file over agent memory. When you learn something durable about this repo — a convention, a workflow gotcha, a design rationale — record it here (or in a repo doc this file points to, e.g. docs/sites/home/switches.md), not in agent memory. AGENTS.md is versioned and shared; memory is not.

Keep this file lean: it should contain only rules, workflows, safety constraints and sharp gotchas an agent needs before starting work. Detailed inventories, topology, service operation and design rationale belong in the canonical document under docs/; summarize only the essential constraint here and link to that document instead of maintaining a second copy.

Claude Code permissions live in two files: .claude/settings.json (versioned, shared — the committed allow list of safe-to-auto-approve commands) and .claude/settings.local.json (personal, gitignored — where interactive "always allow" grants accumulate). Put durable, generally-safe commands in the shared file; leave one-off or workstation-specific grants in the local one.

Overview

Personal Nix flake managing NixOS systems and home-manager configurations for a set of boxes, never a "fleet". It is built around a custom module system layered on top of NixOS/home-manager, not the stock flake nixosConfigurations pattern.

Commands

This repo provides a numtide/devshell (entered via direnv / use flake). The shell defines named commands — prefer them over raw nix invocations. Run a bare command name with no args to see its help, or browse devshell/commands.nix / devshell/install.nix / devshell/vm-tasks.nix.

Common ones:

• fmt — format Nix with nixpkgs-fmt (the canonical formatter here).
• build-system <host> [nix args] — build a NixOS system's toplevel.
• build-n-switch <args> — wraps doas nixos-rebuild --flake ..
• build-home <name> / home-switch — build / switch a home-manager config.
• run-vm <host> — build & boot a system as a dev VM (installs .keys/dev.key into the VM).
• build-iso / build-kexec / build-netboot <host> — alternate build outputs via config.my.buildAs.*.
• check-system <host> [nix args] — evaluate a system (catches eval errors without a full build). Prefer this over build-system to validate a config change — evaluation surfaces module/option errors quickly and cheaply; only do a full build when you specifically need the built artifact.
• deploy <host> and deploy-multi <hosts...> — deploy-rs deployment (uses .keys/deploy.key, --skip-checks). Pass the flake-qualified node, e.g. deploy .#git. The deploy node name is always the system name (deploy-rs.nix keys nodes directly off nixos.systems / home-manager.homes); a system is only a deploy target when config.my.deploy.enable is true (defaults true; auto-disabled for dev VMs and containers). Pass --boot to stage a config as the boot default without live-switching (deploy --boot .#<host>) — the box keeps running its current generation until it reboots. Use this when a live switch would break connectivity mid-change (e.g. a router's WAN VLAN rework), then reboot to cut over.
• ssh-machine <name> [cmd] — SSH to a NixOS system or home-manager config by name. Resolves the target and ssh options (identity, port) from its deploy-rs node, so it needs my.deploy.enable (same gate as deploy). Boxes default to the fish login shell, so pipe multi-statement remote scripts through bash (e.g. ssh-machine <name> bash -s < script.sh) rather than &&/for. If outbound SSH hangs at the publickey step (flaky ssh-agent), disable the agent for the call: SSH_AUTH_SOCK= ssh-machine … (or add -o IdentityAgent=none to a raw ssh).
• ragenix — edit age secrets using .keys/dev.key as identity (see Secrets).
• repl — nix repl .#.
• update-nixpkgs / update-home-manager — bump pinned inputs.

Use the narrowest relevant evaluation while iterating: check-system <host> for a box config, nix eval .#nixfiles.config.nixos.allAssignments --json for assignment generation, or nix build --no-link .#nixfiles.config.nixos.optionsDoc for the option reference. Reserve nix flake check --no-build for final broad validation or reproducing CI. CI builds each attr of .#ci.x86_64-linux (systems, homes, packages, shell) and pushes to the Harmonia binary cache; see .gitea/workflows/ci.yaml and ci/push-to-cache.sh. A separate workflow (.gitea/workflows/update-docs.yaml) regenerates the network-assignment tables and NixOS option reference via nix run .#update-docs-{assignments,options}.

For DNS lookups use drill (ldns) — dig isn't installed in this environment (it fails with exit 127, which is easy to miss if stderr is redirected). E.g. drill -Q @<resolver> <name> A.

For privilege escalation use doas, not sudo — the boxes don't install sudo (it fails with command not found). E.g. doas ip link set <if> up.

For ad-hoc packages prefer pkgs#<name> over nixpkgs#<name> (e.g. nix run pkgs#python3): pkgs is a system registry alias for the same pinned nixpkgs the boxes are built from, so it resolves from the local store instead of fetching a different channel.

Architecture

The mechanics in this section have expanded human-readable write-ups under docs/: docs/architecture.md (module system), docs/networking.md (assignments, topology, meshes) and docs/deployment.md (deploy-rs, devshell, secrets, CI). This section stays the terse agent version; consult those for depth.

The custom module system

flake.nix does not call nixosSystem per host directly. Instead it evalModules over ./nixos, ./home-manager, ./deploy-rs.nix, and the per-host files listed in the configs list in flake.nix. That evaluation produces a top-level config (self.nixfiles) from which the real flake outputs are derived:

• nixos.systems.<name> → nixosConfigurations.<name>
• home-manager.homes.<name> → homeConfigurations.<name>
• nixos.modules / home-manager.modules → nixosModules / homeModules
• deploy-rs.rendered → deploy

nixos/default.nix and home-manager/default.nix define the systemOpts / homeOpts submodules and the mkSystem / mkHome functions that actually invoke eval-config.nix / homeManagerConfiguration. To add a new host: create a box file that sets nixos.systems.<name> = { ... }, then add its path to the configs list in flake.nix.

Multiple nixpkgs channels

Four pkgs sets are threaded everywhere as pkgsFlakes / pkgs' (and hmFlakes for home-manager): unstable, stable, mine (a personal nixpkgs fork), mine-stable. Each system/home picks its channel via nixpkgs / home-manager / hmNixpkgs options (e.g. nixpkgs = "mine-stable"). Modules receive pkgs' = an attrset of all channels for the current system.

lib.my and the my option namespace

lib/default.nix extends lib with a my attrset (helpers like mkOpt', mkBoolOpt', mkDefault', inlineModule', mkDefaultSystemsPkgs, homeStateVersion). It also pulls in:

• lib.my.net — network/CIDR helpers from the libnetRepo input. Used heavily for IP math.
• lib.my.c — shared constants from lib/constants.nix (UIDs/GIDs, kernel package selection, nginx snippets, per-network domains/prefixes, etc.). Reuse these rather than hardcoding.
• lib.my.dns — DNS helpers (lib/dns.nix).

Custom modules add options under the my.* namespace (e.g. my.secrets, my.build, my.tmproot, my.server). Use mkOpt'/mkBoolOpt' for option declarations to match style.

Modules and module lists

Module sets are registered in nixos/modules/_list.nix and home-manager/modules/_list.nix (name → path), which become nixos.modules / home-manager.modules and are applied to every system/home. To add a shared module, drop the file in nixos/modules/ (or home-manager/modules/) and add an entry to the relevant _list.nix.

Network assignments

Each system declares assignments.<name> (in its nixos.systems.<host> block) with IPv4/IPv6 addresses, gateways, domains, MTU, etc. These are aggregated into allAssignments (passed to every module) and there is an assertion that fails on duplicate IPs. Host networking (networking.hostName, domain) defaults from the internal assignment.

Hosts / "boxes"

Per-host configs live under nixos/boxes/<host> (some are single .nix files, some directories with nested VMs/containers under e.g. colony/vms). Many "systems" are VMs or containers managed via the vms / containers modules and the l2mesh VXLAN module.

For a human-readable map of what is actually deployed (per-box roles, services and networking), see README.md and docs/ (index at docs/README.md; box pages under docs/sites/, docs/remote/, docs/mobile/). Keep these in sync when adding, removing or repurposing a box or service. The network-assignment tables are consolidated in docs/networking.md (one per site, CI-generated from allAssignments between <!-- assignments: <site> --> markers); box pages link to that section. Write the prose and let the updater refresh the tables.

Home routers (nixos/boxes/home/routing-common)

river and stream share routing-common, a function of an index; keep common HA behavior there and box-specific WAN behavior in the respective box file. Client-facing gateway and DNS services must use the floating VIPs. routing-common only declares the inert wan-online.target; each box wires its own reachability mechanism. See docs/networking.md#router-ha and the router box pages for the design and operational detail. Keep pair-wide behavior in docs/networking.md; router pages should document only their WAN, platform and other box-specific responsibilities.

The easy-to-mix-up implementation details are that lib.my.networkdAssignment and lib.my.mkVLAN live under lib.my, networkd snippet constants such as networkd.noL3 live under lib.my.c, and interface MTU belongs in the .network's linkConfig.MTUBytes.

Home switches (jim / dave / brian)

These switches are not managed by the flake, and changing them is out-of-band and hard to revert. Read docs/sites/home/switches.md before WAN or VLAN work, always confirm before applying a switch change, and keep the documented layout and lib.my.c.home.vlans in sync.

Home wireless APs (vibe / wave)

These APs are not managed by the flake; only their DNS records are. Read and update docs/sites/home/aps.md when changing an AP or its VLAN layout.

Secrets

age-encrypted secrets in secrets/, managed with ragenix. Each module declares my.secrets.files.<name> and my.secrets.key (the host pubkey to encrypt for). secrets.nix (the ragenix rules file) is generated by reading every system's declared secrets and computing the recipient key list (always including .keys/dev.pub). Edit secrets with the ragenix devshell command, which supplies .keys/dev.key as the identity. The .keys/ directory (dev + deploy private keys) is required for editing secrets, deploying, and running dev VMs.

Conventions

• Format with nixpkgs-fmt (fmt). 2-space indent, inherit (...) blocks at the top of let — prefer inherit (lib) mkOption ...; (and bare use) over qualifying inline as lib.mkOption. Ask before running fmt — some files aren't canonically formatted, so fmt can reindent a whole file and bury a logical change in whitespace churn. Match the surrounding style by hand and leave formatting to the user unless they ask.
• Comment where it genuinely aids understanding, but not for trivial/obvious code — match the file's existing (fairly sparse) comment density. When adding something general, comment its general purpose, not the specific change or one-off reason it was introduced for.
• Prefer lib.my helpers (mkOpt', mkBoolOpt', mkDefault') and lib.my.c constants over reimplementing.
• New shared functionality → a module in */modules/ + entry in _list.nix, options under my.*.
• New host → box file under nixos/boxes/ + entry in the configs list in flake.nix.
• Custom packages live in pkgs/ and are registered in pkgs/default.nix; the overlay is exposed as overlays.default.
• In prose and commit messages, quote code-like identifiers (commands, options, paths, package and attribute names) in backticks.
• Keep docs and prose plain — avoid vague AI-tell filler. In particular use "layout"/"structure" rather than "shape", and "General" rather than "cross-cutting topics"; name things directly instead of reaching for umbrella words.
• For network connectivity, use the concrete term — "interface", "connection", "network attachment" or the network's name — rather than calling it a "leg".
• Call the systems "boxes", never "machines" or "fleet", except where "machine" is part of a command, option or upstream technical term such as QEMU's machine type.
• Commit subjects follow area/scope: Capitalized summary (e.g. nixos/home: ...); keep logically distinct changes in separate commits. Aim for 50-character subjects and do not exceed 72 characters. Wrap commit bodies at 72 columns. A concise body describing the change and its rationale is welcome when the subject alone does not provide enough context.

Documentation

Human-readable docs live under docs/ (index: docs/README.md). Box pages are under docs/sites/<site>/, docs/remote/, docs/mobile/. A box that itself hosts sub-systems (containers/nested VMs) gets a directory named for it with a README.md and the child pages beneath it (e.g. shill/README.md + shill/containers/*.md, sfh/README.md). When a site and its physical box share a name, the site keeps the README.md and the box page stays alongside it (for example sites/colony/README.md and sites/colony/colony.md).

Box page layout (match the existing pages): H1 + a one-line intro; a short bullet list of Source / Host / nixpkgs; an optional hardware inventory or VPS resource-allocation section; ## Role; ## Network assignments that links to networking.md#box-assignments (never inline the table); one ## section per topic; ## Notable config files last. Keep non-hardware platform details in their topical sections rather than moving them with the inventory. A box without static assignments still gets the section with a short explanation instead of a generated-table link.

Structure and layout:

• Use tables for lists of structured items (BGP peers, forwarded ports, vhosts, containers, VMs, VLANs). Make the item name the link; don't add a separate Page/Docs column.
• Break up long prose: any bullet running past ~4 lines over several distinct facts becomes a ### subheading (lead sentence + nested bullets). Don't leave walls of long bullets.
• Prefer durable concepts and named configuration identifiers over copying exact numbers that are tunable, generated or likely to drift. Exact values are appropriate when they are useful parts of the inventory or interface: VM resource allocations, hardware-fixed properties, network and protocol identifiers, exposed service ports, and safety or recovery values. Describe mutable implementation tunables by purpose and link to their source instead of duplicating the current value.
• Per-site index pages (docs/sites/*/README.md, docs/remote/README.md, and docs/mobile/README.md) use one table listing boxes only; don't repeat that inventory in a diagram. A box's containers / nested VMs are tabulated on that box's own page. The global docs/README.md is the exception: it may show them in high-level site diagrams, but should not add a second detailed inventory outside those diagrams.

De-dup by ownership — each fact has one home:

• Shared cross-box fabric (the AS211024 mesh, Tailscale/headscale topology, the BGP overview, the WireGuard-tunnel summary) is documented once in docs/networking.md; box pages give a one-line summary and link to it.
• Site-wide network definitions (prefixes, VLANs, router VIPs and router HA) also live in docs/networking.md; site pages summarize and link to the canonical section.
• Box-specific detail (a box's own BGP peers, the WireGuard tunnels it terminates, its services) lives on the box page; networking.md carries only a per-box summary that links out.
• Addresses represented by generated assignments or extraAssignments live only in the assignment tables; handwritten box and workload inventories link there instead of copying them. Addresses outside that data model (such as external peers or service endpoints) stay with the topic that owns them.

Generated content: the network-assignment tables in networking.md and the option reference (docs/reference/nixos-options.md) are CI-generated (nix run .#update-docs-{assignments,options}) — don't hand-edit between the <!-- ... --> markers; write the prose and let the updater refresh the tables.

Keep docs current: when you add, remove or repurpose a box or service, update its box page, the relevant site-index README.md, and any affected prose in networking.md (the assignment/option tables refresh via CI). This is the same "prefer docs over agent memory" rule from the top of this file.