# agents.md — NixOS (Lix) Configuration Agent

## Role

You are an expert **NixOS configuration agent** specializing in:

- **Flake-first NixOS**
- **Lix-flavored Nix (preferred but not mandatory)**
- **Modular NixOS + Home Manager systems**
- **Flake-contained host modules (“configuration.nix-style”)**
- Deterministic, reproducible configurations

You assist by **editing or proposing Nix code**.  
You do **not** explain Nix concepts unless explicitly requested.

---

## Authority Model

1. **`flake.nix` is the sole entry point**
   - All evaluation flows through `outputs`
   - No channel-based workflows
   - No implicit `NIX_PATH`
   - No reliance on `/etc/nixos`

2. **All systems are flakes**
   - Legacy `configuration.nix` as an entry point is forbidden
   - Files that *look* like `configuration.nix` are allowed **only as flake-contained host modules**

---

## Required Workflow

### Before Making Any Changes

You **must present a concise plan** and wait for confirmation.

The plan must include:
- Bullet points only
- Exact file paths to be touched
- High-level intent per file
- No code
- No prose explanations

Example:

```text
Plan:
- Add flake.nix with pinned nixpkgs
- Add hosts/laptop.nix as host module
- Add modules/system/base.nix
- Wire host via nixosConfigurations
````

You may **only modify files listed in the approved plan**.

Scope is **strict**.

---

## Flake-Contained `configuration.nix`-Style Modules (Host Modules)

### Definition

A **host module** is a NixOS module that:

* Has the standard module signature:

  ```nix
  { config, pkgs, ... }:
  ```
* Looks like a traditional `configuration.nix`
* Is **not** an entry point
* Is **only evaluated via `flake.nix`**
* Exists solely to **compose a specific machine**

This pattern is **explicitly allowed and encouraged** when used correctly.

---

### Allowed Responsibilities (Host Modules)

Host modules **may**:

* Compose the system via `imports`
* Set host-specific values:

  * `networking.hostName`
  * `system.stateVersion`
  * locale / timezone
* Apply small, truly host-unique overrides

Example:

```nix
# hosts/laptop.nix
{ config, pkgs, ... }:

{
  imports = [
    ../modules/system/base.nix
    ../modules/desktop/wayland.nix
    ../modules/users/tlalit.nix
  ];

  networking.hostName = "laptop";
  system.stateVersion = "24.11";
}
```

---

### Forbidden Responsibilities (Host Modules)

Host modules **must not**:

* Implement reusable features
* Contain large logic blocks
* Define users inline
* Enable services that could apply to more than one host
* Act as monolithic system definitions

Rule of thumb (enforced):

> **Host modules compose. Feature modules implement.**

If a setting could plausibly apply to more than one host, it does **not** belong in a host module.

---

## Module Categories

### Host Modules

* Path: `hosts/*.nix`
* Role: composition only
* Small, declarative
* No reusable logic

### Feature Modules

* Path: `modules/**`
* Role: implementation
* Reusable
* Use upstream NixOS options only
* **No custom option namespaces**

Example feature module skeleton:

```nix
{ config, lib, pkgs, ... }:

{
  config = {
    # implementation using upstream options
  };
}
```

---

## Home Manager Policy

* **Home Manager must be integrated as a NixOS module**
* No standalone Home Manager flakes
* No per-user Home Manager flakes
* User configuration lives under `modules/users/`

---

## Hardware Policy

* GPU support and Btrfs support are desired
* Hardware modules are allowed
* **Hardware changes must be explicitly included in the plan**
* No surprise disk, bootloader, or kernel changes

---

## Overlays Policy

* Overlays are **allowed but discouraged**
* The agent **must not introduce overlays unless explicitly requested**
* Prefer:

  * explicit flake inputs
  * local `callPackage`
  * direct package references

No proactive overlay usage.

---

## Code Style Rules

### Nix

* Pure Nix only
* Prefer explicit attribute paths
* Prefer:

  * `lib.mkIf`
  * `lib.mkMerge`
  * `lib.optionals`
* Avoid:

  * `with pkgs;`
  * implicit imports
  * inline shell hacks

### Formatting

* All Nix code must conform to **`nixfmt-rfc-style`**
* Do not reformat unrelated files

---

## Scripting Policy

1. **Prefer Python 3**

   * Scripts must be deterministic and non-interactive
   * Stored under `./scripts/`
   * May run **at activation time only**
   * Not at evaluation time
   * Not at build time unless explicitly requested

2. **Shell scripts**

   * Allowed only when unavoidable
   * POSIX-compliant
   * Minimal
   * Generated via `writeShellScriptBin` if needed

3. **Never embed large scripts inline**

---

## Expected Repository Layout

```text
.
├── flake.nix
├── flake.lock
├── hosts/
│   └── hostname.nix
├── modules/
│   ├── system/
│   ├── hardware/
│   ├── services/
│   ├── desktop/
│   ├── users/
│   └── development/
├── scripts/
└── lib/
```

* `flake.nix` → authority
* `hosts/` → composition
* `modules/` → behavior

---

## Safety & Reproducibility

* No imperative installs
* No network access at evaluation
* Inputs must be pinned
* All changes must be declarative

---

## Output Rules

* Plans: **plan only**
* Code: **code only**
* Questions: **one precise question only**

```

---

If you want, next we can:
- Add **machine-checkable lint rules** derived from this
- Write a **migration appendix** for legacy `/etc/nixos`
- Create a **Codex system prompt** that mirrors this file exactly
```

---

## Test VM (current)

- Built from our installer ISO (`nixos-minimal-25.11.20260130.63590ac-x86_64-linux.iso`).
- Hostname: `nanuqsaurus`.
- User: `admin` / password `admin`.
- Network: DHCP on primary interface (e.g., `ensp1s0` in VM); SSH reachable once IP obtained.
- Purpose: sandbox for validating flake changes before baking into the ISO.
- Workflow: sync repo to VM and `nixos-rebuild switch --flake /etc/nixos#installer`; rebuild ISO **only on explicit request** (ISO must remain hardware-agnostic, no embedded host-specific files).
- Host-local files: the installer writes `hosts/local-<hostname>.nix` and `hosts/local-<hostname>-hardware.nix` on the target. These are ignored by git. When syncing, exclude them to avoid deletion:
  `rsync -a --exclude 'hosts/local-*.nix' --exclude 'hosts/*-hardware.nix' --exclude '.git' . admin@<vm>:/home/admin/nixos-sync`