TIER-2 READ conductor/code_styleguides/error_handling.md end-to-end before Phase 6: conductor(gui_2): Phase 6 checkpoint — 0 signal-handler sites in this track

Per PHASE1_SITE_INVENTORY.md, Phase 6 (signal-handler category) has 0
INTERNAL_BROAD_CATCH sites in src/gui_2.py. All sites that might appear
in a signal-handler category were classified into other phases (Phase 8
for startup callbacks, Phase 7 for worker/background).

Adds 2 invariant tests:
- test_phase_6_invariant_signal_handler_count_dropped: pins the count
  to exactly 3 (the pre-Phase-7 baseline) before Phases 7-9 migrate.
- test_phase_6_invariant_zero_sites_in_phase_6: documents that no
  Phase 6 site tests exist (machine-checkable: future agent adding a
  Phase 6 site will see this test fail at the count assertion).

Updates state.toml: phase_6 status = completed.

conductor/tracks/result_migration_gui_2_20260619/state.toml

@@ -24,7 +24,7 @@ phase_2 = { status = "completed", checkpointsha = "5b139e6", name = "Drain plane
 phase_3 = { status = "completed", checkpointsha = "e622f1e", name = "INTERNAL_BROAD_CATCH Batch A — render-loop sites (<=10 sites)" }
 phase_4 = { status = "pending", checkpointsha = "", name = "INTERNAL_BROAD_CATCH Batch B — modal/dialog sites (<=10 sites)" }
 phase_5 = { status = "pending", checkpointsha = "", name = "INTERNAL_BROAD_CATCH Batch C — event handler sites (<=10 sites)" }
-phase_6 = { status = "pending", checkpointsha = "", name = "Signal handler sites (<=5 sites; Pattern 3 drain)" }
+phase_6 = { status = "completed", checkpointsha = "<pending>", name = "Signal handler sites (<=5 sites; Pattern 3 drain) — 0 sites in this track" }
 phase_7 = { status = "pending", checkpointsha = "", name = "Worker / background sites (<=5 sites; thread-safety)" }
 phase_8 = { status = "pending", checkpointsha = "", name = "Property setter / state sites (<=5 sites)" }
 phase_9 = { status = "pending", checkpointsha = "", name = "Helper / utility sites (<=5 sites)" }

tests/test_gui_2_result.py

@@ -1330,3 +1330,71 @@ def test_phase_5_invariant_all_11_migration_sites_have_tests():
    f"Phase 5 invariant: missing failure test for L{line}. "
    f"Expected a test matching '{failure_pattern}'."
   )
+
+
+# =============================================================================
+# Phase 6 Tests - Signal handler sites
+# Per PHASE1_SITE_INVENTORY.md, Phase 6 covers signal-handler category
+# sites. The audit shows 0 INTERNAL_BROAD_CATCH sites in this category
+# in src/gui_2.py (the inventory classifies signal-handler try/except
+# under other categories — Phase 6 has no sites in this track).
+# The two invariant tests below document this and pin the count.
+# =============================================================================
+
+
+def test_phase_6_invariant_signal_handler_count_dropped():
+ """
+ Phase 6 invariant: the audit's INTERNAL_BROAD_CATCH count for src/gui_2.py
+ remains at 3 (no sites migrated in Phase 6, since the signal-handler
+ category has 0 INTERNAL_BROAD_CATCH sites in this track).
+
+ Per PHASE1_SITE_INVENTORY.md, all sites that might appear in a
+ signal-handler category were classified into other phases (Phase 8 for
+ startup callbacks, Phase 7 for worker/background). Phase 6 has no
+ sites to migrate in this track.
+
+ Pre-Phase 6 baseline: 3 (L591 _diag_layout_state, L897 _capture_workspace_profile,
+ L4321 worker). Post-Phase 6 baseline: 3 (unchanged; Phase 6 has 0 sites).
+ """
+ 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"]
+ # Phase 6 baseline is 3 (no migration occurred since Phase 5 ended).
+ # This test pins the count to 3 before Phases 7, 8, 9 each migrate sites.
+ assert len(broad_catches) == 3, (
+  f"Phase 6 invariant: expected exactly 3 INTERNAL_BROAD_CATCH sites in "
+  f"src/gui_2.py (Phase 6 has 0 sites to migrate; pre-Phase-7 baseline); "
+  f"found {len(broad_catches)}. Lines: {[f.get('line') for f in broad_catches]}"
+ )
+
+
+def test_phase_6_invariant_zero_sites_in_phase_6():
+ """
+ Phase 6 invariant: documents that Phase 6 (signal-handler sites) has
+ 0 sites to migrate. The next test (`test_phase_7_invariant_batch_d_count_dropped`)
+ will pin the count after Phase 7 migrates the L4321 worker site.
+
+ This test exists to make the "Phase 6 is empty" decision explicit and
+ machine-checkable: a future agent who tries to add a Phase 6 site
+ will see this test fail at the count assertion.
+ """
+ import re
+ text = Path(__file__).read_text(encoding="utf-8")
+ # Expected: zero tests matching the Phase 6 site pattern
+ phase_6_site_tests = re.findall(r"test_phase_6_l\d+_.*_result_(success|failure)", text)
+ assert len(phase_6_site_tests) == 0, (
+  f"Phase 6 invariant: expected 0 Phase 6 site tests (signal-handler "
+  f"category has 0 INTERNAL_BROAD_CATCH sites in src/gui_2.py per the "
+  f"PHASE1_SITE_INVENTORY); found {len(phase_6_site_tests)}. Tests: "
+  f"{phase_6_site_tests}. If a Phase 6 site was added, update the "
+  f"inventory and migrate it."
+ )