Make images.toml optional

Return an empty image mapping when images.toml is missing and update the regression test to cover that behavior. This lets manifest-builder run without image overrides while still rejecting empty or invalid images.toml files.

Co-Authored-By: Codex Haiku 4.5 <noreply@anthropic.com>

Author: nresare

src/manifest_builder/config.py

@@ -73,19 +73,20 @@ def load_images(config_dir: Path) -> dict[str, str]:
     Returns a dict mapping template variable names to image references, e.g.:
         {"git_image": "alpine/git:2.47.2", "hugo_image": "floryn90/hugo:0.155.3-alpine"}
 
+    If images.toml is absent, returns an empty dict so image overrides remain optional.
+
     Args:
         config_dir: Directory containing images.toml
 
     Returns:
         Dict mapping image variable names to full image references (repo:version)
 
     Raises:
-        FileNotFoundError: If images.toml is not found in config_dir
         ValueError: If images.toml is invalid or missing required fields
     """
     images_file = config_dir / "images.toml"
     if not images_file.exists():
-        raise FileNotFoundError(f"images.toml not found in {config_dir}")
+        return {}
 
     data = tomllib.loads(images_file.read_text())
 

tests/test_config.py

@@ -1102,13 +1102,12 @@ def test_load_images_returns_image_dict(tmp_path: Path) -> None:
     }
 
 
-def test_load_images_raises_when_missing(tmp_path: Path) -> None:
-    """load_images should raise FileNotFoundError when images.toml is missing."""
+def test_load_images_returns_empty_dict_when_missing(tmp_path: Path) -> None:
+    """load_images should return an empty dict when images.toml is missing."""
     conf_dir = tmp_path / "conf"
     conf_dir.mkdir()
 
-    with pytest.raises(FileNotFoundError, match="images.toml not found"):
-        load_images(conf_dir)
+    assert load_images(conf_dir) == {}
 
 
 def test_load_images_converts_hyphens_to_underscores(tmp_path: Path) -> None: