fix(workflows): reject malformed step config on add (#4087)

Assisted-by: GitHub Copilot (model: gpt-5.6-sol, autonomous)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: marcelsafin

src/specify_cli/workflows/catalog.py

@@ -1396,12 +1396,14 @@ def add_catalog(self, url: str, name: str | None = None) -> None:
         data: dict[str, Any] = {"catalogs": []}
         if config_path.exists():
             try:
-                raw = yaml.safe_load(config_path.read_text(encoding="utf-8")) or {}
+                raw = yaml.safe_load(config_path.read_text(encoding="utf-8"))
             except (yaml.YAMLError, OSError, UnicodeDecodeError) as exc:
                 raise StepValidationError(
                     f"Catalog config file is unreadable or malformed: {exc}"
                 ) from exc
-            if not isinstance(raw, dict):
+            if raw is None:
+                raw = {}
+            elif not isinstance(raw, dict):
                 raise StepValidationError(
                     "Catalog config file is corrupted (expected a mapping)."
                 )

tests/test_workflows.py

@@ -9102,6 +9102,23 @@ def test_add_catalog_empty_yaml_file(self, project_dir):
         assert len(data["catalogs"]) == 1
         assert data["catalogs"][0]["url"] == "https://example.com/steps.json"
 
+    @pytest.mark.parametrize("bad", [[], False, 0, ""])
+    def test_add_catalog_rejects_falsy_non_mapping_config(
+        self, project_dir, bad
+    ):
+        from specify_cli.workflows.catalog import StepCatalog, StepValidationError
+
+        config_path = project_dir / ".specify" / "step-catalogs.yml"
+        original = yaml.safe_dump(bad)
+        config_path.write_text(original, encoding="utf-8")
+
+        with pytest.raises(StepValidationError, match="expected a mapping"):
+            StepCatalog(project_dir).add_catalog(
+                "https://example.com/steps.json", "my-steps"
+            )
+
+        assert config_path.read_text(encoding="utf-8") == original
+
     def test_add_catalog_duplicate_rejected(self, project_dir):
         from specify_cli.workflows.catalog import StepCatalog, StepValidationError