TIER-2 READ conductor/code_styleguides/error_handling.md end-to-end before Phase 5: refactor(gui_2): migrate L1284 _populate_auto_slices outline to Result[T] (Phase 5)

Extract _populate_auto_slices_outline_result helper from the
mcp_client.{py,ts_c,ts_cpp}_get_code_outline try/except in
App._populate_auto_slices. Legacy wrapper drains errors to
app._last_request_errors per FR-BC-4 event-handler pattern.

[pre-audit] L1284 INTERNAL_BROAD_CATCH
[post-audit] V count: 14 -> 13 (L1284 removed)

src/gui_2.py

@@ -1265,23 +1265,20 @@ class App:
   self.ai_status = 'paths applied and session reset'
 
  def _populate_auto_slices(self, f_item: models.FileItem) -> None:
-  from src import mcp_client
   import re
   from pathlib import Path
   import os
   proj_dir = str(Path(self.controller.active_project_path).parent.resolve()) if getattr(self, 'controller', None) and self.controller.active_project_path else None
   abs_path = f_item.path if os.path.isabs(f_item.path) else os.path.join(proj_dir or '.', f_item.path)
   mcp_client.configure([{"path": abs_path}], [proj_dir] if proj_dir else None)
-  
-  f_path_lower = f_item.path.lower()
 
-  #TODO(Ed): Exception(Review)
-  try:
-   if   f_path_lower.endswith('.py'):                           outline = mcp_client.py_get_code_outline(abs_path)
-   elif f_path_lower.endswith(('.c', '.h')):                    outline = mcp_client.ts_c_get_code_outline(abs_path)
-   elif f_path_lower.endswith(('.cpp', '.hpp', '.cxx', '.cc')): outline = mcp_client.ts_cpp_get_code_outline(abs_path)
-   else: return
-  except Exception:
+  outline_result = _populate_auto_slices_outline_result(self, f_item, abs_path)
+  if not outline_result.ok:
+   if not hasattr(self, '_last_request_errors'): self._last_request_errors = []
+   self._last_request_errors.append(("_populate_auto_slices.outline", outline_result.errors[0]))
+   return
+  outline = outline_result.data
+  if not outline:
    return
 
   if outline.startswith("ERROR") or outline.startswith("ACCESS DENIED"):
@@ -7730,4 +7727,37 @@ def _render_ast_inspector_file_content_result(app: "App", f_path: str) -> Result
 
 #endregion: Phase 4 Modal/Dialog Result Helpers
 
+#region: Phase 5 Event Handler Result Helpers (result_migration_gui_2_20260619)
+
+def _populate_auto_slices_outline_result(app: "App", f_item, abs_path: str) -> Result[str]:
+ """Drain-aware variant of L1284 _populate_auto_slices outline fetch.
+
+ Extracts the mcp_client.{py,ts_c,ts_cpp}_get_code_outline try/except
+ from App._populate_auto_slices into a Result-returning helper. On success
+ (extension matches and outline fetch succeeded), returns
+ Result(data=outline). On "skip" (no matching extension), returns
+ Result(data=""). On exception, returns Result(data="",
+ 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._populate_auto_slices (L1284 legacy wrapper)]
+ """
+ f_path_lower = f_item.path.lower()
+ try:
+  if   f_path_lower.endswith('.py'):                           return Result(data=mcp_client.py_get_code_outline(abs_path))
+  elif f_path_lower.endswith(('.c', '.h')):                    return Result(data=mcp_client.ts_c_get_code_outline(abs_path))
+  elif f_path_lower.endswith(('.cpp', '.hpp', '.cxx', '.cc')): return Result(data=mcp_client.ts_cpp_get_code_outline(abs_path))
+  else:                                                        return Result(data="")
+ except Exception as e:
+  return Result(data="", errors=[ErrorInfo(
+   kind=ErrorKind.INTERNAL,
+   message=f"AST outline fetch failed for {f_item.path}: {e}",
+   source="gui_2._populate_auto_slices_outline_result",
+   original=e,
+  )])
+
+#endregion: Phase 5 Event Handler Result Helpers
+
 #endregion: MMA