fix: neutral error message for property index deletion (#2098)

The static delete_property_index error prefix asserted a single cause
("Property may not exist") but the DELETE 422 also covers an invalid
index type and the in-flight-reindex mutation guard, whose server
message the prefix contradicted. Name the failed operation instead and
let the appended response body carry the cause, matching the file's
phrasing style. Pin the behavior with a mock test surfacing a
server-style 422 in-flight-reindex message.

Author: g-despot

mock_tests/test_property_reindex.py

@@ -393,6 +393,29 @@ def test_get_property_indexes(
     weaviate_139_mock.check_assertions()
 
 
+def test_delete_property_index_surfaces_server_message(
+    weaviate_139_mock: HTTPServer, client_139: weaviate.WeaviateClient
+) -> None:
+    """A DELETE rejection surfaces the server's cause behind a neutral prefix.
+
+    The 422 mutation guard (in-flight reindex task) carries an actionable server message;
+    the client prefix must only name the failed operation, not assert a cause.
+    """
+    server_message = "cannot delete index: a reindex task is in progress for property 'name'"
+    weaviate_139_mock.expect_request(
+        f"{SCHEMA_PATH}/properties/name/index/searchable",
+        method="DELETE",
+    ).respond_with_json({"error": [{"message": server_message}]}, status=422)
+
+    with pytest.raises(weaviate.exceptions.UnexpectedStatusCodeError) as e:
+        client_139.collections.use(COLLECTION).config.delete_property_index("name", "searchable")
+    assert e.value.status_code == 422
+    assert "Property index may not have been deleted." in e.value.message
+    assert server_message in e.value.message
+    assert "may not exist" not in e.value.message
+    weaviate_139_mock.check_assertions()
+
+
 def test_property_reindex_invalid_input(
     weaviate_139_mock: HTTPServer, client_139: weaviate.WeaviateClient
 ) -> None:

weaviate/collections/config/executor.py

@@ -704,8 +704,8 @@ def resp(res: Response) -> bool:
             response_callback=resp,
             method=self._connection.delete,
             path=path,
-            error_msg="Property may not exist",
-            status_codes=_ExpectedStatusCodes(ok_in=[200], error="property exists"),
+            error_msg="Property index may not have been deleted.",
+            status_codes=_ExpectedStatusCodes(ok_in=[200], error="Delete property index"),
         )
 
     def __check_property_reindex_support(self, feature: str) -> None: