refactor(rag_engine): Result API + NilRAGState (_init_vector_store, _validate_collection_dim, _get_state)

tests/test_rag_engine.py

@@ -77,8 +77,8 @@ def test_rag_collection_dim_mismatch_recreates_collection(mock_get_chroma, mock_
  "Collection expecting embedding with dimension of 3072, got 384".
 
  Expected: RAGEngine.__init__ detects the mismatch, deletes the
- mismatched collection, and recreates it empty so subsequent indexing
- uses the correct dim.
+ mismatched collection via client.delete_collection, and recreates it
+ empty so subsequent indexing uses the correct dim.
  """
  mock_chroma = MagicMock()
  mock_settings = MagicMock()
@@ -104,14 +104,12 @@ 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
-  # 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).
+  # On dim mismatch, _validate_collection_dim_result calls
+  # client.delete_collection(name) then get_or_create_collection(name)
+  # to recreate the collection with the correct dim. The first
+  # get_or_create_collection call was in _init_vector_store_result.
   assert mock_client.get_or_create_collection.call_count == 2
-  mock_client.delete_collection.assert_not_called()
+  mock_client.delete_collection.assert_called_once_with("test")
 
 @patch('src.rag_engine.LocalEmbeddingProvider.embed')
 @patch('src.rag_engine._get_chromadb')