test(tests): TDD for test_execution_sim_live GUI subprocess crash (failing test)

Captures the structural root cause of the test_execution_sim_live
failure: src/gui_2.py:render_response_panel calls imgui.set_window_focus
directly during the render frame. On Windows, the GUI subprocess main
thread has only 1.94 MB of stack; the focus call exhausts it and
crashes the GUI with 0xC00000FD = STATUS_STACK_OVERFLOW.

This test enforces the fix's contract: the render body must NOT call
imgui.set_window_focus directly; it must defer the call via a
_pending_focus_response flag to the next frame's idle phase. Mirrors
the existing _autofocus_response_tab pattern at gui_2.py:5353-5356.

Test currently FAILS on this commit. Will pass after the fix in
src/gui_2.py:render_response_panel and the deferred handler in the
main render loop.

tests/test_extended_sims.py

@@ -69,4 +69,73 @@ def test_execution_sim_live(live_gui: Any) -> None:
  client.set_value('auto_add_history', True)
  sim.run()
  time.sleep(2)
- sim.teardown()
+ sim.teardown()
+
+def test_render_response_panel_defers_set_window_focus() -> None:
+ """Regression test for the GUI subprocess STATUS_STACK_OVERFLOW crash.
+
+ Captures the root cause of the `test_execution_sim_live` failure: the
+ `render_response_panel` function used to call
+ `imgui.set_window_focus("Response")` directly during the render frame.
+ On Windows, the GUI subprocess's main thread has only 1.94 MB of stack
+ (set by Python's PE header). imgui-bundle's native focus call uses
+ ~2-3 MB of C stack, which exceeds the committed size and triggers
+ `0xC00000FD = STATUS_STACK_OVERFLOW`.
+
+ The contract enforced here: the render body MUST defer the call to the
+ next frame's idle phase via a one-shot `_pending_focus_response` flag.
+ The fix mirrors the existing `_autofocus_response_tab` pattern
+ (see `src/gui_2.py:5353-5356`).
+
+ Note: the source function is `render_response_panel` (no underscore).
+ The `_render_response_panel` label in the bug report is the perf-monitor
+ component name, not the function name.
+ """
+ import re
+ gui_path = os.path.abspath(os.path.join(os.path.dirname(__file__), "..", "src", "gui_2.py"))
+ with open(gui_path, "r", encoding="utf-8") as f:
+  src = f.read()
+
+ # Extract the render_response_panel function body. Non-greedy match up
+ # to the next top-level def (or end of file) so nested defs/comments
+ # inside the body are not treated as the boundary.
+ match = re.search(
+  r"def render_response_panel\(app: App\) -> None:.*?(?=\ndef |\Z)",
+  src,
+  re.DOTALL,
+ )
+ assert match is not None, "render_response_panel function not found in src/gui_2.py"
+ body = match.group(0)
+ rest = src[:match.start()] + src[match.end():]
+
+ # 1. The render body MUST NOT call imgui.set_window_focus("Response")
+ #    directly. A direct call during the render frame exhausts the 1.94 MB
+ #    main thread stack of the GUI subprocess and causes STATUS_STACK_OVERFLOW.
+ assert 'imgui.set_window_focus("Response")' not in body, (
+  "render_response_panel still calls imgui.set_window_focus('Response') directly. "
+  "This exhausts the 1.94 MB main thread stack of the GUI subprocess and causes "
+  "STATUS_STACK_OVERFLOW (0xC00000FD). Defer the call to the next frame's idle "
+  "phase by setting app._pending_focus_response = True and handling it in the "
+  "main render loop, mirroring the _autofocus_response_tab pattern."
+ )
+
+ # 2. The render body MUST signal the deferral by setting the flag.
+ assert "_pending_focus_response = True" in body, (
+  "render_response_panel must set _pending_focus_response = True (e.g. "
+  "app._pending_focus_response = True) when _trigger_blink fires. The deferred "
+  "handler in the main render loop will consume the flag on the next frame's "
+  "idle phase and then clear it."
+ )
+
+ # 3. The main render flow (everything outside render_response_panel) MUST
+ #    contain a deferred handler that reads the flag and calls
+ #    imgui.set_window_focus("Response") when the flag is set.
+ assert "app._pending_focus_response" in rest, (
+  "No reference to app._pending_focus_response found outside render_response_panel. "
+  "The main render loop must read the flag and call imgui.set_window_focus('Response') "
+  "when it is set, then clear the flag."
+ )
+ assert 'imgui.set_window_focus("Response")' in rest, (
+  "No imgui.set_window_focus('Response') call found outside render_response_panel. "
+  "The deferred handler in the main render flow must invoke it when the flag is set."
+ )