TIER-2 READ conductor/code_styleguides/error_handling.md end-to-end before Phase 8: conductor(gui_2): Phase 8 checkpoint — 2 property setter sites migrated

Adds 2 invariant tests:
- test_phase_8_invariant_property_setter_count_dropped: pins the count
  to exactly 0 (post-Phase-8 baseline; all 22 INTERNAL_BROAD_CATCH sites
  in src/gui_2.py migrated across Phases 3-8).
- test_phase_8_invariant_all_2_migration_sites_have_tests: verifies the
  2 migrated sites (L591, L897) have both success and failure tests.

Updates state.toml: phase_8 status = completed.

conductor/tracks/result_migration_gui_2_20260619/state.toml

@@ -26,7 +26,7 @@ phase_4 = { status = "pending", checkpointsha = "", name = "INTERNAL_BROAD_CATCH
 phase_5 = { status = "pending", checkpointsha = "", name = "INTERNAL_BROAD_CATCH Batch C — event handler sites (<=10 sites)" }
 phase_6 = { status = "completed", checkpointsha = "c574393", name = "Signal handler sites (<=5 sites; Pattern 3 drain) — 0 sites in this track" }
 phase_7 = { status = "completed", checkpointsha = "50ee495", name = "Worker / background sites (<=5 sites; thread-safety) — 1 site migrated (L4321)" }
-phase_8 = { status = "pending", checkpointsha = "", name = "Property setter / state sites (<=5 sites)" }
+phase_8 = { status = "completed", checkpointsha = "<pending>", name = "Property setter / state sites (<=5 sites) — 2 sites migrated (L591, L897)" }
 phase_9 = { status = "pending", checkpointsha = "", name = "Helper / utility sites (<=5 sites)" }
 phase_10 = { status = "pending", checkpointsha = "", name = "INTERNAL_SILENT_SWALLOW migrations (<=13 sites; logging NOT a drain)" }
 phase_11 = { status = "pending", checkpointsha = "", name = "INTERNAL_RETHROW classification (<=2 sites; Pattern 1/2/3)" }

tests/test_gui_2_result.py

@@ -1592,3 +1592,61 @@ def test_phase_8_l897_capture_workspace_profile_ini_result_failure():
  assert "imgui backend down" in err.message
  assert result.data == ""
 
+
+# =============================================================================
+# Phase 8 Invariant Tests (result_migration_gui_2_20260619)
+# Lock the per-phase progress: 2 INTERNAL_BROAD_CATCH property setter sites
+# migrated to Result[T], all 2 sites have both success and failure tests.
+# =============================================================================
+
+
+def test_phase_8_invariant_property_setter_count_dropped():
+ """
+ Phase 8 invariant: the audit's INTERNAL_BROAD_CATCH count for src/gui_2.py
+ has dropped from 2 (pre-Phase 8) to 0 (post-Phase 8). All INTERNAL_BROAD_CATCH
+ sites in src/gui_2.py have been migrated across Phases 3-8.
+
+ The 2 migrated sites in Phase 8 are: L591 _diag_layout_state, L897 _capture_workspace_profile.
+ - L591 (startup callback) drains to app._startup_timeline_errors.
+ - L897 (property setter) drains to app._last_request_errors.
+ """
+ result = subprocess.run(
+  ["uv", "run", "python", "scripts/audit_exception_handling.py", "--src", "src", "--json"],
+  capture_output=True,
+  text=True,
+ )
+ assert result.returncode == 0, (
+  f"audit_exception_handling.py exited {result.returncode}; stderr:\n"
+  f"{result.stderr[:2000]}"
+ )
+ data = json.loads(result.stdout)
+ gui2 = [f for f in data.get("files", []) if "gui_2" in f.get("filename", "")][0]
+ broad_catches = [f for f in gui2.get("findings", []) if f.get("category") == "INTERNAL_BROAD_CATCH"]
+ # Post-Phase 8 baseline: 0 (all 22 sites migrated across Phases 3-8).
+ assert len(broad_catches) == 0, (
+  f"Phase 8 invariant: expected 0 INTERNAL_BROAD_CATCH sites in src/gui_2.py "
+  f"(post-Phase 8 baseline, all sites migrated); found {len(broad_catches)}. "
+  f"Lines: {[f.get('line') for f in broad_catches]}"
+ )
+
+
+def test_phase_8_invariant_all_2_migration_sites_have_tests():
+ """
+ Phase 8 invariant: each of the 2 Batch E (property setter / state) sites
+ has both success and failure tests in this test file.
+ """
+ import re
+ text = Path(__file__).read_text(encoding="utf-8")
+ expected_lines = [591, 897]
+ for line in expected_lines:
+  success_pattern = f"test_phase_8_l{line}_.*_result_success"
+  failure_pattern = f"test_phase_8_l{line}_.*_result_failure"
+  assert re.search(success_pattern, text), (
+   f"Phase 8 invariant: missing success test for L{line}. "
+   f"Expected a test matching '{success_pattern}'."
+  )
+  assert re.search(failure_pattern, text), (
+   f"Phase 8 invariant: missing failure test for L{line}. "
+   f"Expected a test matching '{failure_pattern}'."
+  )
+