pipeline: add testing improvements for branch-based workflows

Implement dual improvements to enable efficient testing of pipeline changes
without polluting master branch:

1. Add --force flag to create-host script
   - Skip hostname/IP uniqueness validation
   - Overwrite existing host configurations
   - Update entries in flake.nix and terraform/vms.tf (no duplicates)
   - Useful for iterating on configurations during testing

2. Add branch support to bootstrap mechanism
   - Bootstrap service reads NIXOS_FLAKE_BRANCH environment variable
   - Defaults to master if not set
   - Uses branch in git URL via ?ref= parameter
   - Service loads environment from /etc/environment

3. Add cloud-init disk support for branch configuration
   - VMs can specify flake_branch field in terraform/vms.tf
   - Automatically generates cloud-init snippet setting NIXOS_FLAKE_BRANCH
   - Uploads snippet to Proxmox via SSH
   - Production VMs omit flake_branch and use master

4. Update documentation
   - Document --force flag usage in create-host README
   - Add branch testing examples in terraform README
   - Update TODO.md with testing workflow
   - Add .generated/ to gitignore

Testing workflow: Create feature branch, set flake_branch in VM definition,
deploy with terraform, iterate with --force flag, clean up before merging.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

scripts/create-host/README.md

@@ -50,6 +50,23 @@ python -m scripts.create_host.create_host create \
   --dry-run
 ```
 
+### Force Mode (Regenerate Existing Configuration)
+
+Overwrite an existing host configuration (useful for testing):
+
+```bash
+python -m scripts.create_host.create_host create \
+  --hostname test01 \
+  --ip 10.69.13.50/24 \
+  --force
+```
+
+This mode:
+- Skips hostname and IP uniqueness validation
+- Overwrites files in `hosts/<hostname>/`
+- Updates existing entries in `flake.nix` and `terraform/vms.tf` (doesn't duplicate)
+- Useful for iterating on configuration templates during testing
+
 ### Options
 
 - `--hostname` (required): Hostname for the new host
@@ -73,6 +90,10 @@ python -m scripts.create_host.create_host create \
 
 - `--dry-run` (flag): Preview changes without creating files
 
+- `--force` (flag): Overwrite existing host configuration
+  - Skips uniqueness validation
+  - Updates existing entries instead of creating duplicates
+
 ## What It Does
 
 The tool performs the following actions:

scripts/create-host/create_host.py

@@ -45,6 +45,7 @@ def main(
     memory: int = typer.Option(2048, "--memory", help="Memory in MB"),
     disk: str = typer.Option("20G", "--disk", help="Disk size (e.g., 20G, 50G, 100G)"),
     dry_run: bool = typer.Option(False, "--dry-run", help="Preview changes without creating files"),
+    force: bool = typer.Option(False, "--force", help="Overwrite existing host configuration"),
 ) -> None:
     """
     Create a new NixOS host configuration.
@@ -75,11 +76,20 @@ def main(
 
         config.validate()
         validate_hostname_format(hostname)
-        validate_hostname_unique(hostname, repo_root)
+
+        # Skip uniqueness checks in force mode
+        if not force:
+            validate_hostname_unique(hostname, repo_root)
+            if ip:
+                validate_ip_unique(ip, repo_root)
+        else:
+            # Check if we're actually overwriting something
+            host_dir = repo_root / "hosts" / hostname
+            if host_dir.exists():
+                console.print(f"[yellow]⚠[/yellow]  Updating existing host configuration for {hostname}")
 
         if ip:
             validate_ip_subnet(ip)
-            validate_ip_unique(ip, repo_root)
 
         console.print("[green]✓[/green] All validations passed\n")
 
@@ -96,13 +106,14 @@ def main(
         console.print("\n[bold blue]Generating host configuration...[/bold blue]")
 
         generate_host_files(config, repo_root)
-        console.print(f"[green]✓[/green] Created hosts/{hostname}/default.nix")
-        console.print(f"[green]✓[/green] Created hosts/{hostname}/configuration.nix")
+        action = "Updated" if force else "Created"
+        console.print(f"[green]✓[/green] {action} hosts/{hostname}/default.nix")
+        console.print(f"[green]✓[/green] {action} hosts/{hostname}/configuration.nix")
 
-        update_flake_nix(config, repo_root)
+        update_flake_nix(config, repo_root, force=force)
         console.print("[green]✓[/green] Updated flake.nix")
 
-        update_terraform_vms(config, repo_root)
+        update_terraform_vms(config, repo_root, force=force)
         console.print("[green]✓[/green] Updated terraform/vms.tf")
 
         # Success message

scripts/create-host/manipulators.py

@@ -6,21 +6,18 @@ from pathlib import Path
 from models import HostConfig
 
 
-def update_flake_nix(config: HostConfig, repo_root: Path) -> None:
+def update_flake_nix(config: HostConfig, repo_root: Path, force: bool = False) -> None:
     """
-    Add new host entry to flake.nix nixosConfigurations.
+    Add or update host entry in flake.nix nixosConfigurations.
 
     Args:
         config: Host configuration
         repo_root: Path to repository root
+        force: If True, replace existing entry; if False, insert new entry
     """
     flake_path = repo_root / "flake.nix"
     content = flake_path.read_text()
 
-    # Find the closing of nixosConfigurations block
-    # Pattern: "      };\n      packages ="
-    pattern = r"(      \};)\n(      packages =)"
-
     # Create new entry
     new_entry = f"""      {config.hostname} = nixpkgs.lib.nixosSystem {{
         inherit system;
@@ -40,35 +37,47 @@ def update_flake_nix(config: HostConfig, repo_root: Path) -> None:
       }};
 """
 
-    # Insert new entry before closing brace
-    replacement = rf"\g<1>\n{new_entry}\g<2>"
+    # Check if hostname already exists
+    hostname_pattern = rf"^      {re.escape(config.hostname)} = nixpkgs\.lib\.nixosSystem"
+    existing_match = re.search(hostname_pattern, content, re.MULTILINE)
 
-    new_content, count = re.subn(pattern, replacement, content)
+    if existing_match and force:
+        # Replace existing entry
+        # Match the entire block from "hostname = " to "};"
+        replace_pattern = rf"^      {re.escape(config.hostname)} = nixpkgs\.lib\.nixosSystem \{{.*?^      \}};\n"
+        new_content, count = re.subn(replace_pattern, new_entry, content, flags=re.MULTILINE | re.DOTALL)
 
-    if count == 0:
-        raise ValueError(
-            "Could not find insertion point in flake.nix. "
-            "Looking for pattern: '      };\\n      devShells ='"
-        )
+        if count == 0:
+            raise ValueError(f"Could not find existing entry for {config.hostname} in flake.nix")
+    else:
+        # Insert new entry before closing brace
+        # Pattern: "      };\n      packages ="
+        pattern = r"(      \};)\n(      packages =)"
+        replacement = rf"\g<1>\n{new_entry}\g<2>"
+
+        new_content, count = re.subn(pattern, replacement, content)
+
+        if count == 0:
+            raise ValueError(
+                "Could not find insertion point in flake.nix. "
+                "Looking for pattern: '      };\\n      packages ='"
+            )
 
     flake_path.write_text(new_content)
 
 
-def update_terraform_vms(config: HostConfig, repo_root: Path) -> None:
+def update_terraform_vms(config: HostConfig, repo_root: Path, force: bool = False) -> None:
     """
-    Add new VM entry to terraform/vms.tf locals.vms map.
+    Add or update VM entry in terraform/vms.tf locals.vms map.
 
     Args:
         config: Host configuration
         repo_root: Path to repository root
+        force: If True, replace existing entry; if False, insert new entry
     """
     terraform_path = repo_root / "terraform" / "vms.tf"
     content = terraform_path.read_text()
 
-    # Find the closing of locals.vms block
-    # Pattern: "  }\n\n  # Compute VM configurations"
-    pattern = r"(  \})\n\n(  # Compute VM configurations)"
-
     # Create new entry based on whether we have static IP or DHCP
     if config.is_static_ip:
         new_entry = f'''    "{config.hostname}" = {{
@@ -86,15 +95,30 @@ def update_terraform_vms(config: HostConfig, repo_root: Path) -> None:
     }}
 '''
 
-    # Insert new entry before closing brace
-    replacement = rf"{new_entry}\g<1>\n\n\g<2>"
+    # Check if hostname already exists
+    hostname_pattern = rf'^\s+"{re.escape(config.hostname)}" = \{{'
+    existing_match = re.search(hostname_pattern, content, re.MULTILINE)
 
-    new_content, count = re.subn(pattern, replacement, content)
+    if existing_match and force:
+        # Replace existing entry
+        # Match the entire block from "hostname" = { to }
+        replace_pattern = rf'^\s+"{re.escape(config.hostname)}" = \{{.*?^\s+\}}\n'
+        new_content, count = re.subn(replace_pattern, new_entry, content, flags=re.MULTILINE | re.DOTALL)
 
-    if count == 0:
-        raise ValueError(
-            "Could not find insertion point in terraform/vms.tf. "
-            "Looking for pattern: '  }\\n\\n  # Compute VM configurations'"
-        )
+        if count == 0:
+            raise ValueError(f"Could not find existing entry for {config.hostname} in terraform/vms.tf")
+    else:
+        # Insert new entry before closing brace
+        # Pattern: "  }\n\n  # Compute VM configurations"
+        pattern = r"(  \})\n\n(  # Compute VM configurations)"
+        replacement = rf"{new_entry}\g<1>\n\n\g<2>"
+
+        new_content, count = re.subn(pattern, replacement, content)
+
+        if count == 0:
+            raise ValueError(
+                "Could not find insertion point in terraform/vms.tf. "
+                "Looking for pattern: '  }\\n\\n  # Compute VM configurations'"
+            )
 
     terraform_path.write_text(new_content)