test: capture CivArchive failure contract

tests/test_civarchive_failure_contract.py

@@ -0,0 +1,25 @@
+from types import SimpleNamespace
+from unittest.mock import patch
+
+import pytest
+
+from core.sources import civarchive
+
+
+@pytest.mark.parametrize("status_code", [502, 522])
+def test_civarchive_search_preserves_http_failure_message(status_code):
+    response = SimpleNamespace(status_code=status_code, text="")
+
+    with (
+        patch.object(civarchive, "request_source_response", return_value=response),
+        pytest.raises(civarchive.CivArchiveSearchError, match=f"HTTP {status_code}"),
+    ):
+        civarchive._search_page("model.safetensors")
+
+
+def test_civarchive_search_preserves_network_failure_message():
+    with (
+        patch.object(civarchive, "request_source_response", return_value=None),
+        pytest.raises(civarchive.CivArchiveSearchError, match="network error or timeout"),
+    ):
+        civarchive._search_page("model.safetensors")