test: verify real kbqa workflow

backend/tests/unit/test_file_validation.py

@@ -0,0 +1,13 @@
+from pathlib import Path
+
+import pytest
+
+from kbqa.api.errors import AppError
+from kbqa.indexing.loaders import load_document
+
+
+def test_text_loader_rejects_non_utf8(tmp_path: Path) -> None:
+    path = tmp_path / "bad.txt"
+    path.write_bytes(b"\xff\xfe")
+    with pytest.raises(AppError, match="UTF-8"):
+        load_document(path, "txt")