TIER-2 READ conductor/code_styleguides/error_handling.md end-to-end before Phase 8: refactor(gui_2): migrate L591 _diag_layout_state to Result[T] (Phase 8)

Migrate the ini-file-read try/except in App._diag_layout_state (L591) to
the canonical Result[T] pattern:

- Extract _diag_layout_state_ini_text_result(app, ini_path) -> Result[str]
  helper into new Phase 8 Property Setter / State Result Helpers region.
- The legacy _diag_layout_state method calls the helper and drains errors
  to app._startup_timeline_errors (the Phase 2 drain plane for startup
  callbacks).
- The original fallback behavior (early return on read failure, stderr
  write for visibility) is preserved.

Tests:
- test_phase_8_l591_diag_layout_state_ini_text_result_success
- test_phase_8_l591_diag_layout_state_ini_text_result_failure

Audit: INTERNAL_BROAD_CATCH count in src/gui_2.py dropped from 2 to 1
(remaining: L896 _capture_workspace_profile, formerly L897 in inventory).

tests/test_gui_2_result.py

@@ -1506,3 +1506,50 @@ def test_phase_7_invariant_all_1_migration_sites_have_tests():
    f"Expected a test matching '{failure_pattern}'."
   )
 
+
+# =============================================================================
+# Phase 8 Tests - Migration of 2 INTERNAL_BROAD_CATCH property setter sites
+# to Result[T]. Each site gets 2 tests: success and failure.
+# Migration pattern: legacy wrapper drains to app._startup_timeline_errors
+# (for startup callbacks like L591) or app._last_request_errors
+# (for property setters like L897).
+# =============================================================================
+
+
+def test_phase_8_l591_diag_layout_state_ini_text_result_success():
+ """
+ L591 _diag_layout_state_ini_text_result returns Result(data=ini_text) on success.
+
+ The helper wraps the ini-file-read try/except in App._diag_layout_state.
+ On success, returns Result(data=ini_text) where ini_text is the file content.
+ The legacy wrapper drains errors to app._startup_timeline_errors.
+ """
+ from src import gui_2
+ from unittest.mock import MagicMock, patch, mock_open
+ app = MagicMock()
+ with patch("builtins.open", mock_open(read_data="[Window][Provider]\nPos=10,20")):
+  result = gui_2._diag_layout_state_ini_text_result(app, "/proj/manualslop_layout.ini")
+ assert result.ok, f"Expected ok=True on success, got errors: {result.errors}"
+ assert "[Window][Provider]" in result.data
+
+
+def test_phase_8_l591_diag_layout_state_ini_text_result_failure():
+ """
+ L591 _diag_layout_state_ini_text_result returns Result(data="", errors=[ErrorInfo]) on failure.
+
+ When the ini file read raises (e.g., permission error, encoding error),
+ the helper returns Result with ErrorInfo describing the failure and
+ data="" so the caller can still proceed (return early).
+ """
+ from src import gui_2
+ from unittest.mock import MagicMock, patch
+ app = MagicMock()
+ with patch("builtins.open", side_effect=PermissionError("permission denied")):
+  result = gui_2._diag_layout_state_ini_text_result(app, "/proj/manualslop_layout.ini")
+ 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._diag_layout_state_ini_text_result"
+ assert "permission denied" in err.message
+ assert result.data == ""
+