fix(rag): break recursion in _validate_collection_dim

The wipe path called self._init_vector_store() which re-invoked
_validate_collection_dim, causing infinite recursion (RecursionError)
when the dim mismatch test ran with the mock embedding provider.

Re-initialize the vector store INLINE after the rmtree wipe so the
fresh collection is created without going through the validator
again.

src/rag_engine.py

@@ -176,6 +176,9 @@ class RAGEngine:
   # fails on corrupted state in chromadb 1.5.x with
   # "RustBindingsAPI object has no attribute bindings"). Rmtree is
   # reliable and re-creates a fresh empty collection.
+  # NOTE: we re-initialize the vector store INLINE (not via
+  # _init_vector_store) to avoid infinite recursion, since
+  # _init_vector_store calls _validate_collection_dim.
   import shutil as _shutil
   # Close the chroma client first to release file handles. Without
   # this, rmtree fails with WinError 32 on Windows.
@@ -194,7 +197,20 @@ class RAGEngine:
     except Exception as e:
      sys.stderr.write(f"RAG: Failed to wipe chroma dir: {e}\n")
      sys.stderr.flush()
-  self._init_vector_store()
+  # Re-initialize the vector store inline (no recursion).
+  vs_config = self.config.vector_store
+  if vs_config.provider == 'chroma':
+   from src import rag_engine as _re_self
+   os.makedirs(db_path, exist_ok=True)
+   chroma_module = _get_chromadb()
+   if chroma_module is None:
+    raise ImportError("chromadb is not installed")
+   chromadb, _Settings = chroma_module
+   self.client     = chromadb.PersistentClient(path=db_path)
+   self.collection = self.client.get_or_create_collection(name=vs_config.collection_name)
+  elif vs_config.provider == 'mock':
+   self.client     = "mock"
+   self.collection = "mock"
 
  def is_empty(self) -> bool:
   if not self.config.enabled: