Fix Stop button with fullscreen experiments on Windows

[SherlockChiang]

Fixes psychopy/psychopy#7693.

Problem

On Windows, switching focus away from a fullscreen experiment can interrupt the Stop button click before wx emits EVT_BUTTON. The button visibly enters its pressed state, but the existing callback is not invoked and the experiment continues running.

During reproduction with an active fullscreen PsychoPy window, EVT_LEFT_DOWN was received but EVT_BUTTON was not.

Change

Bind the Runner Python Stop button to EVT_LEFT_DOWN on Windows so the existing stopTask() command runs before a fullscreen focus change can interrupt the click.

The button is disabled before calling stopTask() to prevent the corresponding mouse-up from invoking the command a second time. The existing EVT_BUTTON binding remains in place for keyboard activation and for other platforms.

This does not change Job, Popen.kill(), or process-tree termination behavior. Runner and experiments launched from Coder share this Stop path.

Automated tests

Environment:

• Windows 11
• Python 3.11
• wxPython 4.2.5
• PsychoPy dev / 2026.2 at ceafbd09a741efd81b83cd39acb3a86df6e53fc1
• psychopy-app dev

Command:

$env:PYTHONPATH = 'C:\Users\vince\AppData\Local\Temp\opencode\psychopy-dev;src'
.venv\Scripts\python.exe -m pytest tests/test_runner.py tests/test_app.py -q

Result:

2 passed

The new unit test verifies that the Stop button is disabled before stopTask() is called, preventing re-entry while termination yields to the wx event loop. The existing app smoke test launches Builder, Runner, and Coder.

Additional checks:

.venv\Scripts\python.exe -m compileall -q src tests
git diff --check

Both completed successfully.

Windows end-to-end test flow

1. Start a Python experiment through the same Job path used by Runner.
2. Open a PsychoPy visual.Window and continuously call win.flip().
3. Test once with fullscr=False and once with fullscr=True.
4. Bring a wx Stop window to the foreground after the experiment starts.
5. Use wx.UIActionSimulator to issue a real mouse-down and mouse-up over Stop.
6. Route EVT_LEFT_DOWN through RunnerRibbon._stopOnMouseDown().
7. Record EVT_LEFT_DOWN, EVT_BUTTON, the managed process state, and remaining processes.

Windowed result:

fullscr=False
LEFT_DOWN callback entered
terminated
running=False leftDown=1 button=0

Fullscreen result:

fullscr=True
LEFT_DOWN callback entered
terminated
running=False leftDown=1 button=0

In both modes the submitted handler ran, the experiment stopped, and no experiment process remained. The fullscreen result also reproduces the event-level cause: the mouse-down event arrives while the normal button event does not.