TIER-2 READ conductor/code_styleguides/error_handling.md end-to-end before Phase 10: refactor(gui_2): migrate L612 _post_init callback to Result[T] (Phase 10 site 3)

Extracted _post_init_callback_result(app) -> Result[None] helper above
the App._post_init method.
ANTI-SLIMING: full Result[T] propagation (NO pass-after-logging). The
helper returns Result(data=None) on success or Result(data=None,
errors=[ErrorInfo]) on exception (logging NOT a drain per the user's
principle 2026-06-17).

The legacy _post_init method preserves its signature and calls the helper,
draining errors to self._startup_timeline_errors.

Tests: 2 new tests verify both paths (success and RuntimeError).

Audit: L612 reclassified from INTERNAL_SILENT_SWALLOW (10 sites remaining,
was 11). New helper L612 is INTERNAL_COMPLIANT.

src/gui_2.py

@@ -598,7 +598,30 @@ class App:
  def _handle_save_anyway_click(self) -> None:
   self._pending_save_anyway_click = True
 
- def _post_init(self) -> None:
+def _post_init_callback_result(app: "App") -> Result[None]:
+ """Drain-aware variant of App._post_init (L612 INTERNAL_SILENT_SWALLOW).
+
+ Extracts the controller.on_warmup_complete callback registration from
+ App._post_init into a Result-returning helper. On exception, returns
+ Result(data=None, errors=[ErrorInfo]) so the legacy wrapper can drain
+ the error to self._startup_timeline_errors. On success, the lambda
+ callback is registered and Result(data=None) is returned.
+
+ [C: src/gui_2.py:App._post_init (L612 legacy wrapper)]
+ """
+ #Note(Ed): Exception(Thirdparty)
+ try:
+  app.controller.on_warmup_complete(lambda status: _on_warmup_complete_callback(app, status))
+  return Result(data=None)
+ except Exception as e:
+  return Result(data=None, errors=[ErrorInfo(
+   kind=ErrorKind.INTERNAL,
+   message=f"on_warmup_complete callback registration failed: {e}",
+   source="gui_2._post_init_callback_result",
+   original=e,
+  )])
+
+def _post_init(self) -> None:
  theme.apply_current()
  # Register warmup completion callback (sub-track 4 of
  # startup_speedup_20260606). The callback runs on a background
@@ -606,10 +629,10 @@ class App:
  # is safe. The render_warmup_status_indicator() function reads
  # the timestamp to show a brief "ready" tag for 3 seconds.
  if hasattr(self.controller, "on_warmup_complete"):
-   #Note(Ed): Exception(Thirdparty)
+  cb_result = _post_init_callback_result(self)
-   try:
+  if not cb_result.ok:
-    self.controller.on_warmup_complete(lambda status: _on_warmup_complete_callback(self, status))
+   if not hasattr(self, '_startup_timeline_errors'): self._startup_timeline_errors = []
-   except Exception: pass
+   self._startup_timeline_errors.append(("_post_init.callback", cb_result.errors[0]))
   self._diag_layout_state()
 
  def _diag_layout_state(self) -> None:

tests/test_gui_2_result.py

@@ -1815,4 +1815,46 @@ def test_phase_10_l264_resolve_font_path_result_is_relative_to_raises():
   assert err.source == "gui_2._resolve_font_path_result"
 
 
+def test_phase_10_l612_post_init_callback_result_success():
+ """
+ L612 _post_init_callback_result returns Result(data=None) on success.
+
+ The helper extracts the warmup-complete callback registration from
+ App._post_init into a Result-returning helper. On success, it registers
+ the lambda callback via self.controller.on_warmup_complete() and returns
+ Result(data=None).
+ """
+ from unittest.mock import MagicMock
+ import src.gui_2 as gui2_mod
+ app = MagicMock()
+ app.controller = MagicMock()
+ result = gui2_mod._post_init_callback_result(app)
+ assert result.ok, f"Expected ok=True on success, got errors: {result.errors}"
+ assert result.data is None
+ app.controller.on_warmup_complete.assert_called_once()
+
+
+def test_phase_10_l612_post_init_callback_result_failure():
+ """
+ L612 _post_init_callback_result returns Result(data=None, errors=[ErrorInfo]) on failure.
+
+ When self.controller.on_warmup_complete() raises (e.g., controller not
+ ready or invalid callback), the helper converts to ErrorInfo and returns
+ Result(data=None, errors=[ErrorInfo]). The legacy _post_init wrapper
+ drains to self._startup_timeline_errors.
+ """
+ from unittest.mock import MagicMock
+ import src.gui_2 as gui2_mod
+ app = MagicMock()
+ app.controller = MagicMock()
+ app.controller.on_warmup_complete.side_effect = RuntimeError("controller not ready")
+ result = gui2_mod._post_init_callback_result(app)
+ assert not result.ok, f"Expected ok=False on failure, got data: {result.data}"
+ assert result.data is None
+ assert result.errors, "Expected at least one error on failure"
+ err = result.errors[0]
+ assert err.source == "gui_2._post_init_callback_result"
+ assert "controller not ready" in err.message
+
+