Add Lix-based NixOS installer ISO and interactive script

agents.md

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+# 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
+```