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.

src/gui_2.py

@@ -1163,13 +1163,10 @@ class App:
      self.ai_status   = "session reset"
      self.ai_response = ""
     if imgui.menu_item("Generate MD Only", "", False)[0]:
-     try:
-      md, path, *_      = self._do_generate()
-      self.last_md      = md
-      self.last_md_path = path
-      self.ai_status    = f"md written: {path.name}"
-     except Exception as e:
-      self.ai_status = f"error: {e}"
+     result = _show_menus_do_generate_result(self)
+     if not result.ok:
+      if not hasattr(self, '_last_request_errors'): self._last_request_errors = []
+      self._last_request_errors.append(("_show_menus.do_generate", result.errors[0]))
   with imscope.menu("Layout") as (active):
    if active:
     if imgui.menu_item("Save Current...", "", False)[0]:
@@ -7506,6 +7503,31 @@ def _render_main_interface_result(app: "App") -> Result[bool]:
    original=e,
   )])
 
+def _show_menus_do_generate_result(app: "App") -> Result[bool]:
+ """Drain-aware variant of L1171 _show_menus 'Generate MD Only' menu handler.
+
+ Extracts the try/except from the "Generate MD Only" if-branch in
+ App._show_menus into a Result-returning helper. On success, sets
+ app.last_md, app.last_md_path, app.ai_status. On failure, sets
+ app.ai_status to an error message.
+
+ [C: src/gui_2.py:App._show_menus (L1171 legacy wrapper)]
+ """
+ try:
+  md, path, *_      = app._do_generate()
+  app.last_md       = md
+  app.last_md_path  = path
+  app.ai_status     = f"md written: {path.name}"
+  return Result(data=True)
+ except Exception as e:
+  app.ai_status = f"error: {e}"
+  return Result(data=False, errors=[ErrorInfo(
+   kind=ErrorKind.INTERNAL,
+   message=f"Generate MD Only failed: {e}",
+   source="gui_2._show_menus_do_generate_result",
+   original=e,
+  )])
+
 #endregion: Phase 3 Render-Loop Result Helpers
 
 #endregion: MMA