refactor(gui_2): migrate L1171 _show_menus do_generate to Result[T] (Phase 3)

TIER-2 READ conductor/code_styleguides/error_handling.md end-to-end before Phase 3.

Adds _show_menus_do_generate_result(app) -> Result[bool] helper that wraps
the 'Generate MD Only' menu handler try/except in App._show_menus. The
legacy if-branch in App._show_menus becomes a thin call that drains
errors to _last_request_errors.

Audit: BROAD_CATCH count 22 -> 21, COMPLIANT count 15 -> 16. Tests: 2/2 pass.

tests/test_gui_2_result.py

@@ -335,4 +335,47 @@ def test_phase_3_l1123_render_main_interface_result_failure():
  assert result.errors, "Expected at least one error on failure"
  err = result.errors[0]
  assert err.source == "gui_2._render_main_interface_result"
- assert "render blew up" in err.message
+ assert "render blew up" in err.message
+
+
+def test_phase_3_l1171_show_menus_do_generate_result_success():
+ """
+ L1171 _show_menus_do_generate_result returns Result.ok=True on success.
+
+ The helper wraps the "Generate MD Only" try/except in App._show_menus.
+ On success, sets app.last_md, app.last_md_path, app.ai_status and
+ returns Result(data=True).
+ """
+ from src import gui_2
+ from unittest.mock import MagicMock
+ app = MagicMock()
+ mock_md   = MagicMock(name="mock_md")
+ mock_path = MagicMock(name="mock_path")
+ mock_path.name = "out.md"
+ app._do_generate.return_value = (mock_md, mock_path)
+ result = gui_2._show_menus_do_generate_result(app)
+ assert result.ok, f"Expected ok=True on success, got errors: {result.errors}"
+ assert result.data is True
+ assert app.last_md is mock_md
+ assert app.last_md_path is mock_path
+ assert "md written" in app.ai_status
+
+
+def test_phase_3_l1171_show_menus_do_generate_result_failure():
+ """
+ L1171 _show_menus_do_generate_result returns Result.ok=False on failure.
+
+ When _do_generate raises, the helper sets app.ai_status to an error
+ message and returns Result(data=False, errors=[ErrorInfo]).
+ """
+ from src import gui_2
+ from unittest.mock import MagicMock
+ app = MagicMock()
+ app._do_generate.side_effect = RuntimeError("generate blew up")
+ result = gui_2._show_menus_do_generate_result(app)
+ assert not result.ok, f"Expected ok=False on failure, got data: {result.data}"
+ assert result.errors, "Expected at least one error on failure"
+ err = result.errors[0]
+ assert err.source == "gui_2._show_menus_do_generate_result"
+ assert "generate blew up" in err.message
+ assert "error" in app.ai_status