diff --git a/src/app_controller.py b/src/app_controller.py
index 02342559..e2e6f8ae 100644
--- a/src/app_controller.py
+++ b/src/app_controller.py
@@ -3954,6 +3954,18 @@ class AppController:
   self.temperature = 0.0
   self.top_p = 1.0
   self.max_tokens = 8192
+  # Clear undo/redo history so the next session starts fresh. Without
+  # this, prior tests in the same live_gui session leave stale entries
+  # that interfere with tests like tests/test_undo_redo_sim.py that
+  # assume btn_reset provides a clean history baseline.
+  if hasattr(self, 'hook_server') and self.hook_server and getattr(self.hook_server, 'app', None) is not None:
+   app = self.hook_server.app
+   if hasattr(app, 'history'):
+    app.history._undo_stack.clear()
+    app.history._redo_stack.clear()
+   if hasattr(app, '_last_ui_snapshot'):   app._last_ui_snapshot = None
+   if hasattr(app, '_pending_snapshot'):   app._pending_snapshot = False
+   if hasattr(app, '_state_to_push'):      app._state_to_push  = None
 
  def _handle_compress_discussion(self) -> None:
   def worker() -> "Result[None]":