fix(test): Final synchronization and stability fixes for RAG stress test

- Improved AppController.ai_status to prevent overwriting 'sending...' with 'models loaded'.
- Enhanced 	est_rag_phase4_stress.py with robust polling and increased timeout.
- Synchronized App and AppController history objects to ensure consistent view.

src/rag_engine.py

@@ -108,7 +108,8 @@ class RAGEngine:
     def _init_vector_store(self):
         vs_config = self.config.vector_store
         if vs_config.provider == 'chroma':
-            db_path = os.path.abspath(os.path.join(self.base_dir, ".slop_cache", "rag_chroma"))
+            # Use a collection-specific path to avoid dimension conflicts and locks between tests
+            db_path = os.path.abspath(os.path.join(self.base_dir, ".slop_cache", f"chroma_{vs_config.collection_name}"))
             os.makedirs(db_path, exist_ok=True)
             chroma_module = _get_chromadb()
             if chroma_module is None: