Add Jinja2 template validation test and pre-commit hook (#45)

* Remove escaped chars in comments

* Add Jinja2 template validation test and pre-commit hook

Catch template syntax errors early with a unit test that parses and
renders the default cloud-init template, and a pre-commit hook that
validates all templates in dropkit/templates/ on change.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

.pre-commit-config.yaml

@@ -34,6 +34,16 @@ repos:
         types: [python]
         pass_filenames: false
 
+  # Jinja2 template validation
+  - repo: local
+    hooks:
+      - id: jinja2-check
+        name: jinja2 template syntax
+        entry: uv run python -c "import sys; from jinja2 import Template; [Template(open(f).read()) for f in sys.argv[1:]]"
+        language: system
+        files: ^dropkit/templates/.*\.yaml$
+        types: [file]
+
   # Shell script linting
   - repo: https://github.com/koalaman/shellcheck-precommit
     rev: v0.10.0

dropkit/templates/default-cloud-init.yaml

@@ -1,5 +1,5 @@
 #cloud-config
-# Warning: This whole file will be evaluated by Jinja. Escape any special literals (`{{`, `{%`, `{#`).
+# Warning: This whole file will be evaluated by Jinja. Escape any special literals
 
 # Update and upgrade system packages
 package_update: true

tests/test_cloudinit.py

@@ -0,0 +1,53 @@
+"""Tests for cloud-init template parsing and rendering."""
+
+from jinja2 import Template, TemplateSyntaxError
+
+from dropkit.config import Config
+
+
+def _load_default_template() -> str:
+    """Load the default cloud-init template content."""
+    path = Config.get_default_template_path()
+    return path.read_text()
+
+
+def test_default_template_parses():
+    """Verify the default template is valid Jinja2 syntax."""
+    content = _load_default_template()
+    try:
+        Template(content)
+    except TemplateSyntaxError as exc:
+        raise AssertionError(f"Template has Jinja2 syntax error: {exc}") from exc
+
+
+def test_default_template_renders():
+    """Verify the template renders with sample variables."""
+    content = _load_default_template()
+    template = Template(content)
+    rendered = template.render(
+        username="testuser",
+        full_name="Test User",
+        email="test@example.com",
+        ssh_keys=["ssh-ed25519 AAAAC3... test@host"],
+        tailscale_enabled=True,
+    )
+    assert "testuser" in rendered
+    assert "ssh-ed25519 AAAAC3... test@host" in rendered
+    assert "git config --global user.name 'Test User'" in rendered
+    assert "git config --global user.email 'test@example.com'" in rendered
+    assert "tailscale" in rendered
+
+
+def test_default_template_renders_without_tailscale():
+    """Verify the Tailscale section is absent when disabled."""
+    content = _load_default_template()
+    template = Template(content)
+    rendered = template.render(
+        username="testuser",
+        full_name="Test User",
+        email="test@example.com",
+        ssh_keys=["ssh-ed25519 AAAAC3... test@host"],
+        tailscale_enabled=False,
+    )
+    assert "testuser" in rendered
+    assert "tailscale.com/install.sh" not in rendered