diff --git a/src/app_controller.py b/src/app_controller.py
index c40a4aaa..02342559 100644
--- a/src/app_controller.py
+++ b/src/app_controller.py
@@ -3893,6 +3893,14 @@ class AppController:
   self.ui_ai_input = ""
   self.ui_manual_approve = False
   self.ui_auto_add_history = False
+  # Reset ui_files_base_dir to a sane default so a prior live_gui test
+  # that set a temp/relative path via set_value('files_base_dir', ...)
+  # does not pollute the session-scoped subprocess with a dead path.
+  # See tests/test_rag_visual_sim.py and tests/test_visual_sim_mma_v2.py
+  # for the original polluters. Per Tier 1 investigation:
+  # docs/reports/INVESTIGATION_rag_phase4_final_verify_20260627.md
+  self.ui_files_base_dir = self.project.get("files", {}).get("base_dir", ".")
+  self.ui_shots_base_dir = self.project.get("screenshots", {}).get("base_dir", ".")
   self.active_track = None
   self.active_tier = None
   self.mma_status = 'idle'
diff --git a/tests/test_rag_visual_sim.py b/tests/test_rag_visual_sim.py
index 3d780abe..a43f9e3a 100644
--- a/tests/test_rag_visual_sim.py
+++ b/tests/test_rag_visual_sim.py
@@ -15,26 +15,33 @@ from src import api_hook_client
 def test_rag_full_lifecycle_sim(live_gui):
  client = api_hook_client.ApiHookClient()
  assert client.wait_for_server(timeout=15), "Hook server did not start"
- 
+
  # 1. Setup mock project data
- test_dir = tempfile.mkdtemp()
+ # Per Tier 1 investigation (docs/reports/INVESTIGATION_rag_phase4_final_verify_20260627.md):
+ # Use a temp dir under tests/artifacts/ (NOT tempfile.mkdtemp() which defaults
+ # to C:\Users\Ed\AppData\Local\Temp\tmpXXXX and pollutes the session-scoped
+ # subprocess's ui_files_base_dir with a dead path that persists across
+ # live_gui tests). Also restore files_base_dir and rag_enabled in finally
+ # to prevent state leakage into subsequent live_gui tests.
+ test_dir = tempfile.mkdtemp(dir="tests/artifacts", prefix="rag_visual_sim_")
+ previous_files_base_dir = client.get_value('files_base_dir')
  try:
   (Path(test_dir) / "test_file.txt").write_text("This is a test file about RAG integration. It should be indexed.")
   (Path(test_dir) / "other_file.py").write_text("# This is another file\ndef hello():\n print('world')")
-  
+
   # 2. Configure project through Hook API
-  client.set_value('files_base_dir', test_dir)
+  client.set_value('files_base_dir', str(Path(test_dir).resolve()))
   client.set_value('rag_enabled', True)
   client.set_value('rag_source', 'mock') # Use mock to avoid sentence-transformers dependency in CI
-  
+
   # 3. Verify initial status
   status = client.get_value('rag_status')
   assert status in ['idle', 'ready', 'initializing...'], f"Unexpected initial status: {status}"
-  
+
   # 4. Trigger Rebuild Index
   print("[SIM] Triggering index rebuild...")
   client.click('btn_rebuild_rag_index')
-  
+
   # 5. Wait for status transition
   # Wait for 'indexing...'
   found_indexing = False
@@ -44,9 +51,9 @@ def test_rag_full_lifecycle_sim(live_gui):
     found_indexing = True
     break
    time.sleep(0.1)
-  
+
   print(f"[SIM] Found indexing: {found_indexing}")
-  
+
   # Wait for 'ready'
   success = False
   for _ in range(50):
@@ -57,35 +64,48 @@ def test_rag_full_lifecycle_sim(live_gui):
    if "error" in status.lower():
     pytest.fail(f"RAG indexing failed: {status}")
    time.sleep(0.2)
-  
+
   assert success, f"RAG indexing timed out. Final status: {status}"
   print("[SIM] RAG indexing SUCCESS.")
-  
+
   # 6. Verify retrieval visualization
   # We simulate a response that has RAG context prepended
   # Since we are testing GUI visualization, we'll manually inject a message into the discussion
   # that contains the RAG marker, then verify the GUI state if possible.
   # However, verifying ImGui internal render state via Hook API is limited to exposed fields.
   # We've already verified the wiring of settings and status.
-  
+
   # One final check: toggle RAG off and verify
   client.set_value('rag_enabled', False)
   assert client.get_value('rag_enabled') is False
-  
+
  finally:
-  shutil.rmtree(test_dir)
+  # Restore state to prevent pollution of session-scoped subprocess.
+  # ui_files_base_dir and rag_enabled are sticky; without restoration,
+  # the next live_gui test (e.g. test_rag_phase4_final_verify) inherits
+  # the dead temp path and its RAG search silently no-ops on missing files.
+  try:
+   client.set_value('rag_enabled', False)
+  except Exception:
+   pass
+  if previous_files_base_dir is not None:
+   try:
+    client.set_value('files_base_dir', previous_files_base_dir)
+   except Exception:
+    pass
+  shutil.rmtree(test_dir, ignore_errors=True)
 
 @pytest.mark.integration
 def test_rag_settings_persistence_sim(live_gui):
  client = api_hook_client.ApiHookClient()
  assert client.wait_for_server(timeout=15)
- 
+
  # Change settings
  client.set_value('rag_chunk_size', 1234)
  client.set_value('rag_chunk_overlap', 56)
- 
+
  # Verify they were set in the controller
  assert client.get_value('rag_chunk_size') == 1234
  assert client.get_value('rag_chunk_overlap') == 56
- 
+
  print("[SIM] RAG settings persistence simulation PASSED.")
diff --git a/tests/test_visual_sim_mma_v2.py b/tests/test_visual_sim_mma_v2.py
index 4d568b52..66b109d3 100644
--- a/tests/test_visual_sim_mma_v2.py
+++ b/tests/test_visual_sim_mma_v2.py
@@ -71,10 +71,15 @@ def test_mma_complete_lifecycle(live_gui) -> None:
  time.sleep(0.3)
  client.set_value('gcli_path', f'"{sys.executable}" "{os.path.abspath("tests/mock_gemini_cli.py")}"')
  time.sleep(0.3)
- client.set_value('files_base_dir', 'tests/artifacts/temp_workspace')
+ # Per Tier 1 investigation: do NOT change files_base_dir here and do NOT
+ # click btn_project_save. The previous version set files_base_dir to
+ # 'tests/artifacts/temp_workspace' and persisted it via btn_project_save,
+ # which polluted the session-scoped subprocess's ui_files_base_dir (and
+ # the workspace's manual_slop.toml) with a test-only path that persisted
+ # into subsequent live_gui tests (e.g. test_rag_phase4_final_verify).
+ # The MMA lifecycle does not depend on a specific files_base_dir — the
+ # mock_gemini_cli returns canned responses regardless.
  time.sleep(0.3)
- client.click('btn_project_save')
- time.sleep(1.0)   # one full second — let GUI process all set_value tasks
 
  # ------------------------------------------------------------------
  # Stage 2: Start epic planning