docs: update all references from hosts/ to glue/ and variants/

- Update README.md structure section
- Update DEVELOPMENT.md, EXTERNAL_MODULES.md, INVENTORY.md
- Update GitHub Copilot instructions
- Update PROXMOX_LXC.md references
- Clarify new directory organization and purpose

.github/copilot-instructions.md

@@ -26,8 +26,9 @@ This is a **NixOS system configuration repository** that uses:
 - **`flake.nix`**: Entry point - inputs and outputs only
 - **`inventory.nix`**: Fleet definitions - host configurations
 - **`users.nix`**: User account definitions
-- **`hosts/`**: Host generation logic and hardware types
-- **`sw/`**: Software configurations organized by system type
+- **`variants/`**: Hardware type modules (desktop, laptop, surface, lxc, wsl, etc.)
+- **`glue/`**: Fleet generation logic and common system configuration
+- **`sw/`**: Software configurations by system type
 - **`installer/`**: Build artifact generation (ISO, LXC, etc.)
 - **`templates/`**: Templates for external configurations
 

README.md

@@ -54,18 +54,21 @@ users.nix                 # User account definitions
 
 flake.lock                # Locked dependency versions
 
-hosts/                    # Host generation logic
-├── default.nix           # Main host generator
+variants/                 # Hardware type modules (exportable as nixosModules)
+├── default.nix           # Auto-exports all variant types
+├── nix-desktop.nix       # Desktop workstations
+├── nix-laptop.nix        # Laptop systems
+├── nix-surface.nix       # Surface Pro tablets
+├── nix-lxc.nix           # LXC containers
+├── nix-wsl.nix           # WSL instances
+├── nix-zima.nix          # ZimaBoard systems
+└── nix-ephemeral.nix     # Diskless/netboot systems
+
+glue/                     # Fleet generation and common configuration
+├── fleet.nix             # Processes inventory.nix to generate all hosts
+├── common.nix            # Common NixOS configuration (all hosts)
 ├── boot.nix              # Boot and filesystem configuration
-├── common.nix            # Common system configuration
-├── user-config.nix       # User configuration integration
-└── types/                # Hardware type modules
-    ├── nix-desktop.nix
-    ├── nix-laptop.nix
-    ├── nix-surface.nix
-    ├── nix-lxc.nix
-    ├── nix-wsl.nix
-    └── nix-ephemeral.nix
+└── user-config.nix       # User account and home-manager integration
 
 sw/                       # Software configurations by system type
 ├── default.nix           # Software module entry point

docs/DEVELOPMENT.md

@@ -87,7 +87,7 @@ athenix.users.newuser = {
 };
 ```
 
-2. Enable on hosts in `inventory.nix`:
+2. Enable on fleet in `inventory.nix`:
 
 ```nix
 nix-laptop = {
@@ -294,7 +294,7 @@ For system config:
 ```nix
 # inventory.nix
 nix-lxc = {
-  devices."server" = builtins.fetchGit {
+  devices."server".external = builtins.fetchGit {
     url = "https://git.factory.uga.edu/org/server-config";
     rev = "abc123...";
   };

docs/EXTERNAL_MODULES.md

@@ -28,26 +28,42 @@ External system modules provide host-specific NixOS configurations.
 
 ### Usage
 
-In `inventory.nix`, reference an external module as a device:
+In `inventory.nix`, reference an external module using the `external` field:
 
 ```nix
 nix-lxc = {
   devices = {
-    # Inline configuration
+    # Inline configuration (traditional method)
     "local-server" = {
       athenix.sw.type = "headless";
       services.nginx.enable = true;
     };
     
-    # External module
-    "remote-server" = builtins.fetchGit {
+    # External module (lazy evaluation - fetched only when building this host)
+    "remote-server".external = builtins.fetchGit {
       url = "https://git.factory.uga.edu/org/server-config";
       rev = "abc123def456...";  # Must pin to specific commit
     };
+    
+    # External module with additional local config
+    "mixed-server" = {
+      external = builtins.fetchGit {
+        url = "https://git.factory.uga.edu/org/server-config";
+        rev = "abc123def456...";
+      };
+      # Additional local overrides
+      athenix.users.admin.enable = true;
+      services.openssh.permitRootLogin = "no";
+    };
   };
 };
 ```
 
+**Key Features:**
+- **Lazy Evaluation**: External modules are only fetched when building the specific host
+- **Efficient Rebuilds**: Other hosts can be rebuilt without fetching unrelated external modules
+- **Submodule Support**: Works with Git submodules without affecting other hosts
+
 ### Repository Structure
 
 ```
@@ -99,8 +115,8 @@ server-config/
 
 When a host is built, modules load in this order:
 
-1. Hardware type module (from `hosts/types/nix-*.nix`)
-2. Host common configuration (from `hosts/common.nix`)
+1. Hardware type module (from `variants/nix-*.nix`)
+2. Common system configuration (from `glue/common.nix`)
 3. Software type module (from `sw/{type}/`)
 4. User NixOS modules (from `users.nix` - `nixos.nix` files)
 5. Device-specific overrides (from `inventory.nix`)

docs/INVENTORY.md

@@ -123,11 +123,11 @@ nix-surface = {
 
 ### Method 4: External Module
 
-Reference a Git repository instead of inline configuration:
+Reference a Git repository using the `external` field (lazy evaluation):
 
 ```nix
 nix-lxc = {
-  devices."builder" = builtins.fetchGit {
+  devices."builder".external = builtins.fetchGit {
     url = "https://git.factory.uga.edu/org/builder-config";
     rev = "abc123...";
   };

installer/PROXMOX_LXC.md

@@ -46,7 +46,7 @@ Add the host to `inventory.nix` with the `nix-lxc` type or ensure it has the app
 }
 ```
 
-Your host type configuration (`hosts/types/nix-lxc.nix`) should include:
+Your host type configuration (`variants/nix-lxc.nix`) should include:
 
 ```nix
 {