diff --git a/tests/clients/test_tui_themes.py b/tests/clients/test_tui_themes.py
index 2ea6f4f..0d1eef1 100644
--- a/tests/clients/test_tui_themes.py
+++ b/tests/clients/test_tui_themes.py
@@ -24,6 +24,44 @@
     settings_module._tui_settings = None
 
 
+@pytest.fixture(autouse=True)
+def mock_tui_api(monkeypatch: pytest.MonkeyPatch) -> None:
+    """Mock the backend REST api so these tests never hit a live server.
+
+    The mount worker resolves a session and replays its history through
+    ``load_history``. Against a live backend that replay lands a moment after
+    the test injected its stream events and wipes the chat, so a theme test
+    that looks for the streaming bubble finds none — pass/fail depended on
+    whether a Navi server happened to listen on 8099.
+    """
+    import clients.terminal.api as api_module
+
+    async def fake_create_session(profile_id: str | None = None) -> dict:
+        return {"session_id": "test-session", "profile_id": profile_id or "navi_code"}
+
+    async def fake_get_session(session_id: str) -> dict:
+        return {"session_id": session_id, "profile_id": "navi_code"}
+
+    async def fake_list_sessions() -> list[dict]:
+        return []
+
+    async def fake_get_profile_model(profile_id: str) -> str | None:
+        return "configured-model"
+
+    async def fake_list_terminals(session_id: str) -> list[dict]:
+        return []
+
+    async def fake_get_todos(session_id: str) -> dict:
+        return {"tasks": []}
+
+    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)
+    monkeypatch.setattr(api_module, "get_profile_model", fake_get_profile_model)
+    monkeypatch.setattr(api_module, "list_terminals", fake_list_terminals)
+    monkeypatch.setattr(api_module, "get_todos", fake_get_todos)
+
+
 @pytest.mark.anyio
 async def test_themes_command_opens_picker() -> None:
     async with NaviCodeTui(new_session=True).run_test() as pilot: