TIER-2 READ conductor/code_styleguides/error_handling.md end-to-end before Phase 10: refactor(gui_2): migrate L1647 render_main_interface focus_response to Result[T] (Phase 10 site 8)

Extracted _focus_response_window_result() -> Result[None] helper above
the call site in render_main_interface.
ANTI-SLIMING: full Result[T] propagation (NO bare-except+pass). The
helper returns Result(data=None) on success or Result(data=None,
errors=[ErrorInfo]) on exception (logging NOT a drain per the user's
principle 2026-06-17).

The legacy render_main_interface code preserves its behavior, calls
the helper, drains errors to app._last_request_errors.

Tests: 2 new tests verify both paths (success and RuntimeError).

Audit: L1647 reclassified from INTERNAL_SILENT_SWALLOW (6 sites remaining,
was 7). New helper L1647 is INTERNAL_COMPLIANT.

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
+
+