test(baseline): add 3 Phase 8 invariant tests (mcp_client SS=0, MIG=0)

TIER-2 READ conductor/code_styleguides/error_handling.md end-to-end before Phase 8.

Phase 8 = mcp_client silent-swallow + UNCLEAR + nested BC cleanup:
- 5 INTERNAL_SILENT_SWALLOW sites migrated (L171 _is_allowed via Path.is_relative_to;
  L1661+L1666 stop via ErrorInfo accumulation + stdout drain)
- 3 nested BC sites migrated (_search_file, derive_code_path_result, trace)
- mcp_client now has ZERO migration-target sites

Total tests: 25 pass (4 Phase 1 + 3 Phase 2 + 3 Phase 3 + 3 Phase 4 + 3 Phase 5 +
3 Phase 6 + 3 Phase 7 + 3 Phase 8).

Audit: mcp_client BOUNDARY_CONVERSION: 5, INTERNAL_COMPLIANT: 43.
Migration-target: 0 (was 9 after Phase 7).

tests/test_baseline_result.py

@@ -270,4 +270,33 @@ def test_phase7_modules_import_cleanly():
     assert hasattr(src.mcp_client, "get_tree_result")
     assert hasattr(src.mcp_client, "web_search_result")
     assert hasattr(src.mcp_client, "fetch_url_result")
-    assert hasattr(src.mcp_client, "get_ui_performance_result")
+    assert hasattr(src.mcp_client, "get_ui_performance_result")
+
+# ============ Phase 8 tests (3) ============
+
+def test_phase8_mcp_client_silent_swallow_zero():
+ """Phase 8 CRITICAL anti-sliming phase: mcp_client INTERNAL_SILENT_SWALLOW = 0."""
+ data = _audit_live()
+ files = {f["filename"]: f for f in data["files"]}
+ findings = files["src\\mcp_client.py"]["findings"]
+ ss = sum(1 for f in findings if f["category"] == "INTERNAL_SILENT_SWALLOW")
+ assert ss == 0, f"expected mcp_client SS=0 after Phase 8, got {ss}"
+
+
+def test_phase8_mcp_client_total_migration_target_zero():
+ """After Phase 8, mcp_client should have 0 migration-target sites (BC + SS + UNCLEAR)."""
+ data = _audit_live()
+ files = {f["filename"]: f for f in data["files"]}
+ findings = files["src\\mcp_client.py"]["findings"]
+ mig_cats = {"INTERNAL_BROAD_CATCH", "INTERNAL_SILENT_SWALLOW", "UNCLEAR"}
+ total = sum(1 for f in findings if f["category"] in mig_cats)
+ assert total == 0, f"expected mcp_client migration-target=0 after Phase 8, got {total}"
+
+
+def test_phase8_modules_import_cleanly():
+ """Verify mcp_client imports after Phase 8 anti-sliming migrations."""
+ import src.mcp_client
+ # New _result variants from Phase 8 are inside py_find_usages_result and
+ # derive_code_path_result; these are integration tests, not attribute tests.
+ assert hasattr(src.mcp_client, "py_find_usages_result")
+ assert hasattr(src.mcp_client, "derive_code_path_result")