fix(cli): keep monitor repaints safe during prompt handoff

tests/cli/test_subagent_monitor_prompts.py

@@ -1,9 +1,13 @@
 """Blocking prompts reclaim input from the nested monitor without a keypress."""
 import asyncio
+import threading
 from types import SimpleNamespace
 
+import pytest
 
-def test_prompt_paint_yields_monitor_but_ordinary_paint_does_not():
+
+@pytest.mark.parametrize('paint_source', ['modal', 'tick'])
+def test_prompt_paint_yields_monitor_but_ordinary_paint_does_not(monkeypatch, paint_source):
     from hermes_cli.cli_subagent_monitor import SubagentMonitor, build_monitor_application, install_dock
     from hermes_cli.cli_terminal_mixin import CLITerminalMixin
     from prompt_toolkit.input import create_pipe_input
@@ -29,10 +33,34 @@ def test_prompt_paint_yields_monitor_but_ordinary_paint_does_not():
                 task = asyncio.create_task(app.run_async())
                 await asyncio.wait_for(rendered.wait(), 3)
                 try:
+                    rendered.clear()
                     await asyncio.to_thread(CLITerminalMixin._paint_now, cli)
+                    await asyncio.wait_for(rendered.wait(), 3)
                     assert not task.done(), 'ordinary paints must not dismiss the monitor'
+                    loop = asyncio.get_running_loop()
+                    ui_thread = threading.get_ident()
+                    stopped = threading.Event()
+                    task.add_done_callback(lambda _: stopped.set())
+                    schedule = loop.call_soon_threadsafe
+
+                    def schedule_with_teardown(callback, *args, **kwargs):
+                        handle = schedule(callback, *args, **kwargs)
+                        if (callback == app.on_invalidate.fire
+                                and threading.get_ident() != ui_thread):
+                            # Let an already-queued frame see the modal and finish
+                            # teardown while the worker is still in invalidate().
+                            schedule(app._redraw)
+                            assert stopped.wait(3), 'monitor did not finish teardown'
+                        return handle
+
                     setattr(cli, name, {'pending': True})
-                    await asyncio.to_thread(CLITerminalMixin._paint_now, cli)
+                    with monkeypatch.context() as patch:
+                        patch.setattr(loop, 'call_soon_threadsafe', schedule_with_teardown)
+                        if paint_source == 'tick':
+                            patch.setattr(monitor, 'refresh', lambda: True)
+                            await asyncio.to_thread(monitor.tick)
+                        else:
+                            await asyncio.to_thread(CLITerminalMixin._paint_now, cli)
                     done, _ = await asyncio.wait({task}, timeout=1)
                     assert task in done, f'{name} remained hidden behind the monitor'
                     await task