fix(phase3): Resolve remaining test failures and stabilize GUI

- Fixed
ullcontext NameError in gui_2.py.
- Corrected TestMMAApprovalIndicators to call real rendering methods on mock app.
- Updated 	est_history_manager.py to provide required context_files argument to UISnapshot.
- Stabilized 	est_z_negative_flows.py with robust polling for terminal response status and corrected field names.
- Cleaned up debug logging in 
ag_engine.py and pp_controller.py.

src/gui_2.py

@@ -17,7 +17,7 @@ import threading
 import time
 import tomli_w
 import typing
-# from contextlib import ExitStack, nullcontext
+from contextlib import ExitStack, nullcontext
 from defer import defer
 from imgui_bundle import imgui, hello_imgui, immapp, imgui_node_editor as ed, imgui_color_text_edit as ced
 from pathlib import Path
@@ -771,7 +771,7 @@ class App:
   try:
    self._render_main_interface()
   except Exception as e:
-   print(f"ERROR in _gui_func: {e}")
+   sys.stderr.write(f"ERROR in _gui_func: {e}\n")
    traceback.print_exc()
   
   if pushed_prior_tint:

src/rag_engine.py

@@ -18,7 +18,7 @@ def _get_sentence_transformers():
             from sentence_transformers import SentenceTransformer
             _SENTENCE_TRANSFORMERS = SentenceTransformer
         except Exception as e:
-            sys.stderr.write(f"[DEBUG RAG] FAILED to import sentence_transformers: {e}\n")
+            sys.stderr.write(f"FAILED to import sentence_transformers: {e}\n")
             sys.stderr.flush()
             raise e
     return _SENTENCE_TRANSFORMERS
@@ -51,7 +51,7 @@ class LocalEmbeddingProvider(BaseEmbeddingProvider):
             if ST:
                 self.model = ST(model_name)
         except Exception as e:
-            sys.stderr.write(f"[DEBUG RAG] LocalEmbeddingProvider failed to load model {model_name}: {e}. Using dummy embeddings.\n")
+            sys.stderr.write(f"LocalEmbeddingProvider failed to load model {model_name}: {e}. Using dummy embeddings.\n")
             sys.stderr.flush()
 
     def embed(self, texts: List[str]) -> List[List[float]]:
@@ -108,7 +108,6 @@ class RAGEngine:
     def _init_vector_store(self):
         vs_config = self.config.vector_store
         if vs_config.provider == 'chroma':
-            # Use absolute path to avoid confusion during directory cleanup/change
             db_path = os.path.abspath(os.path.join(self.base_dir, ".slop_cache", "rag_chroma"))
             os.makedirs(db_path, exist_ok=True)
             chroma_module = _get_chromadb()