restore comment

src/rag_engine.py

@@ -128,6 +128,18 @@ class RAGEngine:
    return Result(data=None, errors=[ErrorInfo(kind=ErrorKind.CONFIG, message=f"Unknown vector store provider: {vs_config.provider}", source="rag._init_vector_store")])
 
  def _validate_collection_dim_result(self) -> Result[None]:
+  """
+  Detect dimension mismatch between an existing collection's vectors and
+  the current embedding provider's output. When mismatched (e.g. the user
+  switched from Gemini 3072-dim to local 384-dim, or vice versa), the
+  collection is wiped at the directory level (not via delete_collection,
+  which can fail on corrupted state in chromadb 1.5.x with
+  "RustBindingsAPI object has no attribute bindings") so the next
+  index pass populates it with the correct dim. Prevents silent
+  corruption that would later surface as a search error
+  ("Collection expecting embedding with dimension of X, got Y") and
+  hang live_gui tests.
+  """
   if self.collection is None or self.collection == "mock" or self.embedding_provider is None:
    return Result(data=None)
   try: