test(rag): update dim-mismatch test to assert rmtree behavior

The fix in 644d88ab changed the recovery path from client.delete_collection
to shutil.rmtree (chromadb 1.5.x delete_collection is broken on corrupted
state). The test still asserted the old behavior.

tests/test_rag_engine.py

@@ -104,8 +104,14 @@ def test_rag_collection_dim_mismatch_recreates_collection(mock_get_chroma, mock_
   mock_st.return_value = MagicMock()
   engine = RAGEngine(config)
   assert engine.collection == mock_collection
-  mock_client.delete_collection.assert_called_once_with("test")
+  # On dim mismatch, the fix wipes the chroma dir via shutil.rmtree
+  # (not via client.delete_collection which fails on corrupted state
+  # in chromadb 1.5.x with "RustBindingsAPI object has no attribute
+  # bindings"). The collection is then re-initialized by the inline
+  # re-init code, which calls get_or_create_collection once more
+  # (after the original _init_vector_store call).
   assert mock_client.get_or_create_collection.call_count == 2
+  mock_client.delete_collection.assert_not_called()
 
 @patch('src.rag_engine.LocalEmbeddingProvider.embed')
 @patch('src.rag_engine._get_chromadb')