diff --git a/tests/clients/test_tui_app.py b/tests/clients/test_tui_app.py
index b83ab1c..f534887 100644
--- a/tests/clients/test_tui_app.py
+++ b/tests/clients/test_tui_app.py
@@ -25,6 +25,32 @@
     settings_module._tui_settings = None
 
 
+@pytest.fixture(autouse=True)
+def mock_tui_api(monkeypatch: pytest.MonkeyPatch) -> None:
+    """Mock the backend REST api so TUI tests never hit a live server.
+
+    Every test mounts NaviCodeTui, whose _startup worker calls api.create_session /
+    api.get_session and whose _refresh_sessions worker calls api.list_sessions.
+    Without a server these raise and _ctx.session_id stays None, which breaks any
+    test that asserts on the session. Tests that assert on stop_session still
+    monkeypatch it per-test with their own call-tracking list.
+    """
+    import clients.terminal.api as api_module
+
+    def fake_create_session(profile_id: str | None = None) -> dict:
+        return {"session_id": "test-session", "profile_id": profile_id or "navi_code"}
+
+    def fake_get_session(session_id: str) -> dict:
+        return {"session_id": session_id, "profile_id": "navi_code"}
+
+    def fake_list_sessions() -> list[dict]:
+        return []
+
+    monkeypatch.setattr(api_module, "create_session", fake_create_session)
+    monkeypatch.setattr(api_module, "get_session", fake_get_session)
+    monkeypatch.setattr(api_module, "list_sessions", fake_list_sessions)
+
+
 @pytest.mark.anyio
 async def test_tui_mounts_widgets() -> None:
     """The TUI app mounts chat, status, and input widgets."""