TIER-2 READ conductor/code_styleguides/error_handling.md end-to-end before Phase 10: refactor(gui_2): migrate L216 _detect_refresh_rate_win32 to Result[T] (Phase 10 site 1)

Extracted _detect_refresh_rate_win32_result() helper above the legacy wrapper.
ANTI-SLIMING: full Result[T] propagation (NO narrowing+logging). The helper
returns Result(data=rate) on success or Result(data=0.0, errors=[ErrorInfo])
on exception (logging NOT a drain per the user's principle 2026-06-17).

The legacy _detect_refresh_rate_win32() wrapper preserves its signature and
delegates to the helper. The call site in App.__init__ invokes the result
helper directly and drains errors to self._startup_timeline_errors.

Tests: 2 new tests (test_phase_10_l216_detect_refresh_rate_win32_result_success,
test_phase_10_l216_detect_refresh_rate_win32_result_failure) verify both paths.

Audit: L216 reclassified from INTERNAL_SILENT_SWALLOW (12 sites remaining,
was 13). New helper L219 is INTERNAL_COMPLIANT.

src/gui_2.py

@@ -178,13 +178,16 @@ def truncate_entries(entries: list[dict[str, Any]], max_pairs: int) -> list[dict
   if count == target: return entries[i:]
  return entries
 
-def _detect_refresh_rate_win32() -> float:
- """Return the primary display's current refresh rate in Hz, or 0.0 on failure.
+def _detect_refresh_rate_win32_result() -> Result[float]:
+ """Drain-aware variant of _detect_refresh_rate_win32 (L216 INTERNAL_SILENT_SWALLOW).
 
- Uses user32.EnumDisplaySettingsW (ENUM_CURRENT_SETTINGS) which reads the value
- directly from the display driver in microseconds. The previous implementation
- shelled out to PowerShell + WMI (Get-CimInstance Win32_VideoController), which
- cost ~350ms on every startup and blocked the first frame.
+ Extracts the thirdparty ctypes user32.EnumDisplaySettingsW try/except from
+ _detect_refresh_rate_win32 into a Result-returning helper. On exception,
+ returns Result(data=0.0, errors=[ErrorInfo]) so the legacy wrapper can
+ fall back to the safe 0.0 default. On success, returns Result(data=rate)
+ where rate is the detected display frequency in Hz.
+
+ [C: src/gui_2.py:_detect_refresh_rate_win32 (L216 legacy wrapper)]
  """
  #Note(Ed): Exception(Thirdparty)
  try:
@@ -210,12 +213,32 @@ def _detect_refresh_rate_win32() -> float:
   dm        = _DEVMODE()
   dm.dmSize = ctypes.sizeof(_DEVMODE)
   if ctypes.windll.user32.EnumDisplaySettingsW(None, -1, ctypes.byref(dm)):
-   # dmDisplayFrequency is 0 or 1 for "default/hardware" on some drivers.
    if dm.dmDisplayFrequency > 1:
-    return float(dm.dmDisplayFrequency)
- except Exception:
-  pass
- return 0.0
+    return Result(data=float(dm.dmDisplayFrequency))
+  return Result(data=0.0)
+ except Exception as e:
+  return Result(data=0.0, errors=[ErrorInfo(
+   kind=ErrorKind.INTERNAL,
+   message=f"win32 EnumDisplaySettingsW failed: {e}",
+   source="gui_2._detect_refresh_rate_win32_result",
+   original=e,
+  )])
+
+def _detect_refresh_rate_win32() -> float:
+ """Return the primary display's current refresh rate in Hz, or 0.0 on failure.
+
+ Uses user32.EnumDisplaySettingsW (ENUM_CURRENT_SETTINGS) which reads the value
+ directly from the display driver in microseconds. The previous implementation
+ shelled out to PowerShell + WMI (Get-CimInstance Win32_VideoController), which
+ cost ~350ms on every startup and blocked the first frame.
+
+ Legacy wrapper: delegates to _detect_refresh_rate_win32_result. Preserves
+ the original signature (returns float). The call site in App.__init__
+ invokes the result helper directly and drains errors to
+ self._startup_timeline_errors.
+ """
+ result = _detect_refresh_rate_win32_result()
+ return result.data
 
 def _resolve_font_path(font_path: str, assets_dir: Path) -> str:
  """Normalize a configured font path to something hello_imgui can load.