diff --git a/tests/test_project_switch_persona_preset.py b/tests/test_project_switch_persona_preset.py
index 24c7150f..d7233c66 100644
--- a/tests/test_project_switch_persona_preset.py
+++ b/tests/test_project_switch_persona_preset.py
@@ -269,7 +269,6 @@ def test_switch_project_non_blocking(tmp_path, monkeypatch):
     assert ctrl.active_project_path == str(project_b_path)
 
 
-@pytest.mark.skip(reason="Pre-existing test bug: monkeypatches _rebuild_rag_index and _flush_to_project to no-ops, which makes _do_project_switch complete synchronously before _api_generate is called. By the time _api_generate checks is_project_stale(), the io_pool worker has already cleared the flag -> so is_project_stale() returns False and the function continues, hitting the next failure (e.g. KeyError on 'output_dir'). The 409 contract only holds while the io_pool worker is still running. Tracked as pre-existing.")
 def test_api_generate_blocked_while_stale(tmp_path, monkeypatch):
     """_api_generate returns 409 when the project switch is in progress."""
     project_a_path, project_b_path = _setup_two_projects(tmp_path)
@@ -285,6 +284,14 @@ def test_api_generate_blocked_while_stale(tmp_path, monkeypatch):
     ctrl.persona_manager = PersonaManager(Path(project_a_path).parent)
     ctrl._refresh_from_project()
 
+    # Add a sleep to the no-op patches so the io_pool worker is busy
+    # long enough for the subsequent _api_generate call to observe
+    # _project_switch_in_progress=True. Without the sleep, the worker
+    # completes synchronously and is_project_stale() returns False by
+    # the time _api_generate runs.
+    monkeypatch.setattr(ctrl, "_rebuild_rag_index", lambda: time.sleep(0.5))
+    monkeypatch.setattr(ctrl, "_flush_to_project", lambda: time.sleep(0.5))
+
     ctrl._switch_project(str(project_b_path))
     assert ctrl.is_project_stale()
     from fastapi import HTTPException