diff --git a/src/gui_2.py b/src/gui_2.py
index 378a9143..5fd000a3 100644
--- a/src/gui_2.py
+++ b/src/gui_2.py
@@ -1644,10 +1644,32 @@ def render_main_interface(app: App) -> None:
  if app.controller._process_pending_tool_calls(): app._tool_log_dirty = True
  if app._pending_focus_response:
   app._pending_focus_response = False
-  try:
-   imgui.set_window_focus("Response") # type: ignore[call-arg]
-  except:
-   pass
+  focus_result = _focus_response_window_result()
+  if not focus_result.ok:
+   if not hasattr(app, '_last_request_errors'): app._last_request_errors = []
+   app._last_request_errors.append(("render_main_interface.focus_response", focus_result.errors[0]))
+
+def _focus_response_window_result() -> Result[None]:
+ """Drain-aware variant of render_main_interface imgui.set_window_focus try block (L1647 INTERNAL_SILENT_SWALLOW).
+
+ Extracts the thirdparty imgui.set_window_focus("Response") try/except from
+ render_main_interface into a Result-returning helper. On exception (native
+ bundle error, IM_ASSERT), converts to ErrorInfo (logging NOT a drain per
+ the user's principle 2026-06-17). The caller drains to
+ app._last_request_errors.
+
+ [C: src/gui_2.py:render_main_interface (L1647 legacy wrapper)]
+ """
+ try:
+  imgui.set_window_focus("Response") # type: ignore[call-arg]
+  return Result(data=None)
+ except Exception as e:
+  return Result(data=None, errors=[ErrorInfo(
+   kind=ErrorKind.INTERNAL,
+   message=f"imgui.set_window_focus('Response') failed: {e}",
+   source="gui_2._focus_response_window_result",
+   original=e,
+  )])
  #endregion: Process GUI task queue
  
  render_track_proposal_modal(app)
diff --git a/tests/test_gui_2_result.py b/tests/test_gui_2_result.py
index 247d6114..19d2592d 100644
--- a/tests/test_gui_2_result.py
+++ b/tests/test_gui_2_result.py
@@ -2032,4 +2032,40 @@ def test_phase_10_l1466_close_vscode_diff_terminate_result_failure():
  assert "process already exited" in err.message
 
 
+def test_phase_10_l1647_focus_response_window_result_success():
+ """
+ L1647 _focus_response_window_result returns Result(data=None) on success.
+
+ The helper extracts the imgui.set_window_focus("Response") try/except from
+ render_main_interface into a Result-returning helper. On success, returns
+ Result(data=None).
+ """
+ from unittest.mock import MagicMock, patch
+ import src.gui_2 as gui2_mod
+ with patch("src.gui_2.imgui.set_window_focus", return_value=None):
+  result = gui2_mod._focus_response_window_result()
+ assert result.ok, f"Expected ok=True on success, got errors: {result.errors}"
+ assert result.data is None
+
+
+def test_phase_10_l1647_focus_response_window_result_failure():
+ """
+ L1647 _focus_response_window_result returns Result(data=None, errors=[ErrorInfo]) on failure.
+
+ When imgui.set_window_focus("Response") raises (e.g., native bundle
+ error, IM_ASSERT), the helper converts to ErrorInfo. The caller
+ (render_main_interface) drains to self._last_request_errors.
+ """
+ from unittest.mock import patch
+ import src.gui_2 as gui2_mod
+ with patch("src.gui_2.imgui.set_window_focus", side_effect=RuntimeError("IM_ASSERT: window scope")):
+  result = gui2_mod._focus_response_window_result()
+ assert not result.ok, f"Expected ok=False on failure, got data: {result.data}"
+ assert result.data is None
+ assert result.errors, "Expected at least one error on failure"
+ err = result.errors[0]
+ assert err.source == "gui_2._focus_response_window_result"
+ assert "IM_ASSERT" in err.message
+
+