TIER-2 READ conductor/code_styleguides/error_handling.md end-to-end before Phase 5: refactor(gui_2): migrate L5920 render_external_editor_panel config to Result[T] (Phase 5)

Extract _render_external_editor_panel_config_result helper from the external
editor config rendering try/except in render_external_editor_panel. Legacy
wrapper drains errors to app._last_request_errors per FR-BC-4
event-handler pattern.

[pre-audit] L5920 INTERNAL_BROAD_CATCH
[post-audit] V count: 5 -> 4 (L5920 removed)

src/gui_2.py

@@ -5838,47 +5838,11 @@ def render_external_editor_panel(app: App) -> None:
  from src.external_editor import get_default_launcher
  imgui.text("External Editor for Diff Viewing")
  imgui.separator()
- try:
+ ext_config_result = _render_external_editor_panel_config_result(app)
-  launcher = get_default_launcher(app.config)
+ if not ext_config_result.ok:
-  editors = launcher.config.editors
+  if not hasattr(app, '_last_request_errors'): app._last_request_errors = []
-  default_name = launcher.config.default_editor
+  app._last_request_errors.append(("_render_external_editor_panel_config", ext_config_result.errors[0]))
-  if not editors:
+  imgui.text_colored(C_TC(), f"Error: {ext_config_result.errors[0].message}")
-   imgui.text_colored(C_REQ(), "  No editors configured")
-   imgui.text("")
-   imgui.text("Add editors in config.toml:")
-   imgui.text("  [tools.text_editors.vscode]")
-   imgui.text('  path = "C:\\\\path\\\\to\\\\code.exe"')
-   imgui.text('  diff_args = ["--diff"]')
-   imgui.text("")
-   imgui.text("  [tools.text_editors.notepadpp]")
-   imgui.text('  path = "C:\\\\path\\\\to\\\\notepad++.exe"')
-   imgui.text('  diff_args = ["-multiInst", "-nosession"]')
-   imgui.text("")
-   imgui.text("Then set default in [tools.default_editor]")
-  else:
-   imgui.text("Default Editor:")
-   editor_names = sorted(list(editors.keys()))
-   if default_name and default_name in editor_names: current_idx = editor_names.index(default_name)
-   else:                                             current_idx = 0
-   changed, new_idx = imgui.combo("##editor_combo", current_idx, editor_names)
-   if changed: app._set_external_editor_default(editor_names[new_idx])
-   imgui.text("")
-   imgui.text("Configured Editors:")
-   imgui.separator()
-   for name in editor_names:
-    editor = editors.get(name)
-    if not editor: continue
-    is_default = name == default_name
-    marker = " (default)" if is_default else ""
-    if is_default: imgui.text_colored(C_IN(), f"  {name}{marker}")
-    else:          imgui.text(f"  {name}{marker}")
-    imgui.text(f"    {editor.path}")
-    if editor.diff_args: imgui.textDisabled(f"    diff: {editor.diff_args}")
-   imgui.text("")
-   imgui.text("Config: config.toml [tools.text_editors]")
-   imgui.text("Override: manual_slop.toml default_editor")
- except Exception as e:
-  imgui.text_colored(C_TC(), f"Error: {str(e)}")
 
 def render_approve_script_modal(app: App) -> None:
  """
@@ -8016,6 +7980,69 @@ def _render_text_viewer_window_ced_result(app: "App") -> Result[bool]:
    original=e,
   )])
 
+
+def _render_external_editor_panel_config_result(app: "App") -> Result[bool]:
+ """Drain-aware variant of L5920 render_external_editor_panel config block.
+
+ Extracts the external editor config rendering try/except from
+ render_external_editor_panel into a Result-returning helper. On success,
+ returns Result(data=True). On exception, converts the exception to
+ ErrorInfo 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:render_external_editor_panel (L5920 legacy wrapper)]
+ """
+ from src.external_editor import get_default_launcher
+ try:
+  launcher     = get_default_launcher(app.config)
+  editors      = launcher.config.editors
+  default_name = launcher.config.default_editor
+  if not editors:
+   imgui.text_colored(C_REQ(), "  No editors configured")
+   imgui.text("")
+   imgui.text("Add editors in config.toml:")
+   imgui.text("  [tools.text_editors.vscode]")
+   imgui.text('  path = "C:\\\\path\\\\to\\\\code.exe"')
+   imgui.text('  diff_args = ["--diff"]')
+   imgui.text("")
+   imgui.text("  [tools.text_editors.notepadpp]")
+   imgui.text('  path = "C:\\\\path\\\\to\\\\notepad++.exe"')
+   imgui.text('  diff_args = ["-multiInst", "-nosession"]')
+   imgui.text("")
+   imgui.text("Then set default in [tools.default_editor]")
+  else:
+   imgui.text("Default Editor:")
+   editor_names = sorted(list(editors.keys()))
+   if default_name and default_name in editor_names: current_idx = editor_names.index(default_name)
+   else:                                             current_idx = 0
+   changed, new_idx = imgui.combo("##editor_combo", current_idx, editor_names)
+   if changed: app._set_external_editor_default(editor_names[new_idx])
+   imgui.text("")
+   imgui.text("Configured Editors:")
+   imgui.separator()
+   for name in editor_names:
+    editor = editors.get(name)
+    if not editor: continue
+    is_default = name == default_name
+    marker = " (default)" if is_default else ""
+    if is_default: imgui.text_colored(C_IN(), f"  {name}{marker}")
+    else:          imgui.text(f"  {name}{marker}")
+    imgui.text(f"    {editor.path}")
+    if editor.diff_args: imgui.textDisabled(f"    diff: {editor.diff_args}")
+   imgui.text("")
+   imgui.text("Config: config.toml [tools.text_editors]")
+   imgui.text("Override: manual_slop.toml default_editor")
+  return Result(data=True)
+ except Exception as e:
+  return Result(data=False, errors=[ErrorInfo(
+   kind=ErrorKind.INTERNAL,
+   message=f"Render external editor panel config failed: {e}",
+   source="gui_2._render_external_editor_panel_config_result",
+   original=e,
+  )])
+
 #endregion: Phase 5 Event Handler Result Helpers
 
 #endregion: MMA

tests/test_gui_2_result.py

@@ -1185,3 +1185,44 @@ def test_phase_5_l5786_render_text_viewer_window_ced_result_failure():
  err = result.errors[0]
  assert err.source == "gui_2._render_text_viewer_window_ced_result"
  assert "ced set_text failed" in err.message
+
+
+def test_phase_5_l5920_render_external_editor_panel_config_result_success():
+ """
+ L5920 _render_external_editor_panel_config_result returns Result.ok=True on success.
+
+ The helper wraps the external editor config rendering try/except in
+ render_external_editor_panel. On success, returns Result(data=True).
+ """
+ from src import gui_2
+ from unittest.mock import MagicMock, patch
+ app = MagicMock()
+ app.config = {"tools": {"text_editors": {}, "default_editor": ""}}
+ mock_launcher = MagicMock()
+ mock_launcher.config.editors        = {}
+ mock_launcher.config.default_editor = None
+ with patch("src.external_editor.get_default_launcher", return_value=mock_launcher), \
+   patch.object(gui_2, "imgui", new=MagicMock()):
+  result = gui_2._render_external_editor_panel_config_result(app)
+ assert result.ok, f"Expected ok=True on success, got errors: {result.errors}"
+ assert result.data is True
+
+
+def test_phase_5_l5920_render_external_editor_panel_config_result_failure():
+ """
+ L5920 _render_external_editor_panel_config_result returns Result.ok=False with ErrorInfo on failure.
+
+ When the external editor config rendering raises, the helper converts the
+ exception to ErrorInfo and returns Result(data=False, errors=[ErrorInfo]).
+ """
+ from src import gui_2
+ from unittest.mock import MagicMock, patch
+ app = MagicMock()
+ app.config = {"tools": {"text_editors": {}, "default_editor": ""}}
+ with patch("src.external_editor.get_default_launcher", side_effect=RuntimeError("ext editor config blew up")):
+  result = gui_2._render_external_editor_panel_config_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._render_external_editor_panel_config_result"
+ assert "ext editor config blew up" in err.message