diff --git a/tests/presentation/test_codex_accounts.py b/tests/presentation/test_codex_accounts.py
index 7b88b14e45..c330909856 100644
--- a/tests/presentation/test_codex_accounts.py
+++ b/tests/presentation/test_codex_accounts.py
@@ -431,6 +431,8 @@ def test_existing_busy_pause_reenters_new_readonly_preflight(native, tmp_path):
 def test_native_restart_uses_real_accepted_work_fence_before_app_quit(native, monkeypatch, tmp_path, status):
     from loopx.chat_store import ChatSessionStore
     host_module = importlib.import_module("loopx_codex_provider_routing.native_host")
+    # Model the macOS client on every POSIX test host, as client_host does.
+    monkeypatch.setattr(host_module.sys, "platform", "darwin")
     store = ChatSessionStore(tmp_path / "runtime")
     sid = store.create_session(goal_id="test", agent_id="test", adapter_kind="fake",
                                upstream_thread_id="test", upstream_mode="managed")["session_id"]