TIER-2 READ conductor/code_styleguides/error_handling.md end-to-end before Phase 5: refactor(gui_2): migrate L1367 _apply_pending_patch to Result[T] (Phase 5)

Extract _apply_pending_patch_result helper from the apply_patch_to_file
try/except in App._apply_pending_patch. Legacy wrapper drains errors to
app._last_request_errors per FR-BC-4 event-handler pattern.

[pre-audit] L1367 INTERNAL_BROAD_CATCH
[post-audit] V count: 12 -> 11 (L1367 removed)

src/gui_2.py

@@ -1350,20 +1350,10 @@ class App:
   if not self._pending_patch_text:
    self._patch_error_message = "No patch to apply"
    return
-  #TODO(Ed): Exception(Review)
-  try:
-   base_dir     = str(self.controller.current_project_dir) if hasattr(self.controller, 'current_project_dir') else "."
-   success, msg = apply_patch_to_file(self._pending_patch_text, base_dir)
-   if success:
-    self._show_patch_modal    = False
-    self._pending_patch_text  = None
-    self._pending_patch_files = []
-    self._patch_error_message = None
-    imgui.close_current_popup()
-   else:
-    self._patch_error_message = msg
-  except Exception as e:
-   self._patch_error_message = str(e)
+  patch_result = _apply_pending_patch_result(self)
+  if not patch_result.ok:
+   if not hasattr(self, '_last_request_errors'): self._last_request_errors = []
+   self._last_request_errors.append(("_apply_pending_patch", patch_result.errors[0]))
 
  def _open_patch_in_external_editor(self) -> None:
   self._external_editor_clicked = True
@@ -7785,6 +7775,49 @@ def _populate_auto_slices_file_read_result(app: "App", f_item) -> Result[str]:
    original=e,
   )])
 
+
+def _apply_pending_patch_result(app: "App") -> Result[bool]:
+ """Drain-aware variant of L1367 _apply_pending_patch.
+
+ Extracts the apply_patch_to_file try/except from App._apply_pending_patch
+ into a Result-returning helper. On success (apply_patch_to_file returns
+ (True, msg)), sets app._show_patch_modal=False, app._pending_patch_text=None,
+ app._pending_patch_files=[], app._patch_error_message=None and returns
+ Result(data=True). On failure (apply_patch_to_file returns (False, msg)
+ or raises), sets app._patch_error_message to the error string and returns
+ Result(data=False, errors=[ErrorInfo]).
+
+ The legacy wrapper drains errors to app._last_request_errors (per FR-BC-4
+ event-handler drain pattern; data plane attribute).
+
+ [C: src/gui_2.py:App._apply_pending_patch (L1367 legacy wrapper)]
+ """
+ try:
+  base_dir     = str(app.controller.current_project_dir) if hasattr(app.controller, 'current_project_dir') else "."
+  success, msg = apply_patch_to_file(app._pending_patch_text, base_dir)
+  if success:
+   app._show_patch_modal    = False
+   app._pending_patch_text  = None
+   app._pending_patch_files = []
+   app._patch_error_message = None
+   imgui.close_current_popup()
+   return Result(data=True)
+  else:
+   app._patch_error_message = msg
+   return Result(data=False, errors=[ErrorInfo(
+    kind=ErrorKind.INTERNAL,
+    message=f"apply_patch_to_file returned False: {msg}",
+    source="gui_2._apply_pending_patch_result",
+   )])
+ except Exception as e:
+  app._patch_error_message = str(e)
+  return Result(data=False, errors=[ErrorInfo(
+   kind=ErrorKind.INTERNAL,
+   message=f"Apply pending patch failed: {e}",
+   source="gui_2._apply_pending_patch_result",
+   original=e,
+  )])
+
 #endregion: Phase 5 Event Handler Result Helpers
 
 #endregion: MMA

tests/test_gui_2_result.py

@@ -878,3 +878,48 @@ def test_phase_5_l1293_populate_auto_slices_file_read_result_failure():
  err = result.errors[0]
  assert err.source == "gui_2._populate_auto_slices_file_read_result"
  assert "no such file" in err.message
+
+
+def test_phase_5_l1367_apply_pending_patch_result_success():
+ """
+ L1367 _apply_pending_patch_result returns Result.ok=True on success.
+
+ The helper wraps the apply_patch_to_file try/except in App._apply_pending_patch.
+ On success (apply_patch_to_file returns (True, msg)), returns Result(data=True)
+ and sets app._show_patch_modal=False, app._pending_patch_text=None,
+ app._pending_patch_files=[], app._patch_error_message=None.
+ """
+ from src import gui_2
+ from unittest.mock import MagicMock, patch
+ app = MagicMock()
+ app._pending_patch_text = "--- a/foo.py\n+++ b/foo.py\n@@ -1 +1 @@\n-old\n+new\n"
+ app.controller.current_project_dir = "/proj/foo"
+ with patch.object(gui_2, "apply_patch_to_file", return_value=(True, "patched")), \
+   patch.object(gui_2.imgui, "close_current_popup"):
+  result = gui_2._apply_pending_patch_result(app)
+ assert result.ok, f"Expected ok=True on success, got errors: {result.errors}"
+ assert result.data is True
+ assert app._show_patch_modal is False
+ assert app._patch_error_message is None
+
+
+def test_phase_5_l1367_apply_pending_patch_result_failure():
+ """
+ L1367 _apply_pending_patch_result returns Result.ok=False with ErrorInfo on failure.
+
+ When apply_patch_to_file returns (False, msg) or raises, the helper sets
+ app._patch_error_message to the error message and returns
+ Result(data=False, errors=[ErrorInfo]).
+ """
+ from src import gui_2
+ from unittest.mock import MagicMock, patch
+ app = MagicMock()
+ app._pending_patch_text = "--- a/foo.py\n+++ b/foo.py\n"
+ app.controller.current_project_dir = "/proj/foo"
+ with patch.object(gui_2, "apply_patch_to_file", side_effect=RuntimeError("patch blew up")):
+  result = gui_2._apply_pending_patch_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._apply_pending_patch_result"
+ assert "patch blew up" in err.message