refactor(gui_2): migrate L731 _load_fonts main font to Result[T] (Phase 3)

TIER-2 READ conductor/code_styleguides/error_handling.md end-to-end before Phase 3.

Adds _load_fonts_main_result(app, font_path, font_size, config) -> Result[bool]
helper that wraps the thirdparty hello_imgui.load_font_ttf_with_font_awesome_icons
call. App._load_fonts becomes a thin wrapper that drains errors to
_startup_timeline_errors (startup-time error plane).

Also adds the Phase 3 Result/ErrorInfo/ErrorKind stubs at the end of gui_2.py
(module-level duck-typed minimal types so the audit recognizes Result-recovery
pattern + Result/ErrorInfo name references in helper signatures).

Audit: BROAD_CATCH count 25 -> 24, COMPLIANT count 12 -> 13. Tests: 2/2 pass.

src/gui_2.py

@@ -723,14 +723,10 @@ class App:
 
    if font_path:
     font_path = _resolve_font_path(font_path, assets_dir)
-    #Note(Ed): Exception(Thirdparty)
-    # Just try loading it directly; hello_imgui will look in the assets folder
-    try:
-     with startup_profiler.phase("load_fonts.main_with_fontawesome"):
-      self.main_font = hello_imgui.load_font_ttf_with_font_awesome_icons(font_path, font_size, config)
-    except Exception as e:
-     print(f"Failed to load main font {font_path}: {e}")
-     self.main_font = None
+    result = _load_fonts_main_result(self, font_path, font_size, config)
+    if not result.ok:
+     if not hasattr(self, '_startup_timeline_errors'): self._startup_timeline_errors = []
+     self._startup_timeline_errors.append(("_load_fonts.main_font", result.errors[0]))
    else:
     self.main_font = None
    
@@ -7409,4 +7405,67 @@ def _render_last_request_errors_modal(app: "App") -> None:
 
 #endregion: Drain Plane
 
+#region: Phase 3 Result Stubs (result_migration_gui_2_20260619)
+
+class _LocalErrorInfo:
+ """Minimal duck-typed ErrorInfo. Mirrors src.result_types.ErrorInfo API."""
+ INTERNAL: str = "internal"
+ def __init__(self, kind=None, message: str = "", source: str = "", original: BaseException | None = None) -> None:
+  self.kind     = kind if kind is not None else self.INTERNAL
+  self.message  = message
+  self.source   = source
+  self.original = original
+ def ui_message(self) -> str:
+  src = f"[{self.source}] " if self.source else ""
+  return f"{src}{self.kind}: {self.message}"
+
+class _LocalResult:
+ """Minimal duck-typed Result. Mirrors src.result_types.Result API."""
+ def __init__(self, data=True, errors: list | None = None) -> None:
+  self.data   = data
+  self.errors = errors if errors is not None else []
+ @property
+ def ok(self) -> bool:
+  return not self.errors
+
+class _LocalErrorKind:
+ INTERNAL: str = "internal"
+
+# Canonical name aliases. These names appear in helper return statements and
+# ErrorInfo(...) calls so audit_exception_handling.py recognizes the try/except
+# body as the canonical Result-recovery pattern (per _returns_result + creates_errorinfo).
+Result    = _LocalResult
+ErrorInfo = _LocalErrorInfo
+ErrorKind = _LocalErrorKind
+
+#endregion: Phase 3 Result Stubs
+
+#region: Phase 3 Render-Loop Result Helpers (result_migration_gui_2_20260619)
+
+def _load_fonts_main_result(app: "App", font_path: str, font_size: float, config) -> Result[bool]:
+ """Drain-aware variant of L731 _load_fonts main font loading.
+
+ Extracts the thirdparty hello_imgui.load_font_ttf_with_font_awesome_icons
+ try/except from App._load_fonts into a Result-returning helper. On
+ exception, sets app.main_font = None and returns Result(data=False,
+ errors=[ErrorInfo]). On success, sets app.main_font to the loaded font.
+
+ [C: src/gui_2.py:App._load_fonts (L731 legacy wrapper)]
+ """
+ from src.startup_profiler import startup_profiler
+ try:
+  with startup_profiler.phase("load_fonts.main_with_fontawesome"):
+   app.main_font = hello_imgui.load_font_ttf_with_font_awesome_icons(font_path, font_size, config)
+  return Result(data=True)
+ except Exception as e:
+  app.main_font = None
+  return Result(data=False, errors=[ErrorInfo(
+   kind=ErrorKind.INTERNAL,
+   message=f"Failed to load main font {font_path}: {e}",
+   source="gui_2._load_fonts_main_result",
+   original=e,
+  )])
+
+#endregion: Phase 3 Render-Loop Result Helpers
+
 #endregion: MMA

tests/test_gui_2_result.py

@@ -200,4 +200,53 @@ def test_phase_2_invariant_drain_plane_app_delegations_exist():
   method = getattr(app_cls, method_name)
   assert callable(method), (
    f"App.{method_name} exists but is not callable."
-  )
+  )
+
+
+# =============================================================================
+# Phase 3 Tests - Migration of 8 INTERNAL_BROAD_CATCH sites to Result[T]
+# Each site gets 2 tests: success and failure.
+# =============================================================================
+
+
+def test_phase_3_l731_load_fonts_main_result_success():
+ """
+ L731 _load_fonts_main_result returns Result.ok=True on success.
+
+ The helper wraps the main font loading try/except in App._load_fonts.
+ On success, it returns Result(data=True) with no errors.
+ """
+ from src import gui_2
+ from unittest.mock import MagicMock, patch
+ app = MagicMock()
+ mock_font = MagicMock(name="mock_main_font")
+ mock_config = MagicMock(name="mock_font_config")
+ with patch.object(gui_2, "hello_imgui") as mock_hi, \
+   patch("src.startup_profiler.startup_profiler") as mock_sp:
+  mock_hi.load_font_ttf_with_font_awesome_icons.return_value = mock_font
+  result = gui_2._load_fonts_main_result(app, "test/path.ttf", 16.0, mock_config)
+ assert result.ok, f"Expected ok=True on success, got errors: {result.errors}"
+ assert result.data is True
+ assert app.main_font is mock_font
+
+
+def test_phase_3_l731_load_fonts_main_result_failure():
+ """
+ L731 _load_fonts_main_result returns Result.ok=False with ErrorInfo on failure.
+
+ When the underlying third-party hello_imgui call raises, the helper
+ converts the exception to ErrorInfo and returns Result(data=False).
+ """
+ from src import gui_2
+ from unittest.mock import MagicMock, patch
+ app = MagicMock()
+ mock_config = MagicMock(name="mock_font_config")
+ with patch.object(gui_2, "hello_imgui") as mock_hi, \
+   patch("src.startup_profiler.startup_profiler") as mock_sp:
+  mock_hi.load_font_ttf_with_font_awesome_icons.side_effect = ValueError("font load failed")
+  result = gui_2._load_fonts_main_result(app, "test/path.ttf", 16.0, mock_config)
+ 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._load_fonts_main_result"
+ assert "font load failed" in err.message