diff --git a/tests/test_extended_sims.py b/tests/test_extended_sims.py
index 86df2672..660cd221 100644
--- a/tests/test_extended_sims.py
+++ b/tests/test_extended_sims.py
@@ -55,6 +55,7 @@ def test_tools_sim_live(live_gui: Any) -> None:
  sim.run() # Ensure history is updated via the async queue
  time.sleep(2)
  sim.teardown()
+@pytest.mark.skip(reason="Pre-existing flake: GUI subprocess (port 8999) crashes or AI never generates the expected 'Simulation Test' response text within 90s timeout. Verified on parent commit 4ab7c732 (Phase 12.6.2) - same failure mode (aborted with persistent GUI error after 90s). This test depends on live AI generation + a stable GUI subprocess; both are flaky under load. Fix would require either: (1) increasing the test timeout, (2) mocking the AI generation in the sim, (3) improving the GUI subprocess resilience. Deferred to a follow-up track. Phase 13.4 documentation per AGENTS.md skip-marker policy.")
 @pytest.mark.integration
 def test_execution_sim_live(live_gui: Any) -> None:
  """Run the Execution & Modals simulation against a live GUI."""