test(gui_2): add 2 Phase 12 invariant tests + Phase 12 checkpoint

Two Phase 12 invariant tests in tests/test_gui_2_result.py verify
UNCLEAR count for src/gui_2.py is 0 after the lazy-loading sentinel
fallback heuristic:

- test_phase_12_invariant_unclear_count_zero: scans audit --json
  output, asserts 0 UNCLEAR findings in gui_2.py (the 2 lazy-loading
  sites in _LazyModule._resolve reclassified as INTERNAL_COMPLIANT)
- test_phase_12_invariant_l65_l69_reclassified: scans audit --json
  output, asserts no UNCLEAR findings in _LazyModule._resolve
  method context

State.toml updates:
- phase_12 status: completed, checkpointsha: f996aa10
- phase_12_complete: true
- unclear_count_zero: true
- t12_0/t12_1/t12_2 marked completed with their commit SHAs

Pre-Phase 12: gui_2.py had 2 UNCLEAR sites (L65 + L69 in
_LazyModule._resolve). Post-Phase 12: 0 UNCLEAR sites, 56
INTERNAL_COMPLIANT sites (was 54; +2 from reclassification).

Phase 12 result_migration_gui_2_20260619.

tests/test_gui_2_result.py

@@ -2478,3 +2478,93 @@ def test_phase_11_invariant_l757_l760_reclassified():
   f"__setattr__/__delattr__); found {len(rethrows)}. "
   f"Sites: {[(f.get('line'), f.get('context'), f.get('snippet')) for f in rethrows]}"
  )
+
+
+# =============================================================================
+# Phase 12 Invariant Tests (result_migration_gui_2_20260619)
+# Lock the UNCLEAR count: 2 sites in _LazyModule._resolve (L65, L69) reclassified
+# as INTERNAL_COMPLIANT via the lazy-loading sentinel fallback heuristic in
+# scripts/audit_exception_handling.py:_try_compliant_pattern (heuristic B).
+# The 2 sites are the lazy-loading sentinel fallback pattern in src/gui_2.py
+# where a proxy class defers a heavy import (numpy, tkinter, etc.) and falls
+# back to a documented sentinel class instance (_FiledialogStub) with an
+# `available: bool = False` flag when the import or attribute access fails.
+# Per the styleguide (error_handling.md:625-690, Re-Raise Patterns) and the
+# lazy-loading pattern guidance, this is the canonical graceful-degradation
+# pattern — NOT silent sliming.
+# =============================================================================
+
+
+def test_phase_12_invariant_unclear_count_zero():
+ """
+ Phase 12 invariant: the audit's UNCLEAR count for src/gui_2.py is now 0.
+ The 2 sites in _LazyModule._resolve (L65, L69) have been reclassified as
+ INTERNAL_COMPLIANT via the new lazy-loading sentinel fallback heuristic
+ in scripts/audit_exception_handling.py:_try_compliant_pattern (heuristic B).
+
+ The heuristic recognizes the canonical pattern:
+   - Enclosing function is in LAZY_LOADER_METHOD_NAMES
+     ({_resolve, _load, _get, _try_load}) — the standard naming for
+     proxy classes that defer a heavy import until first use.
+   - The except body does NOT re-raise.
+   - The except set is in {AttributeError, ImportError, ModuleNotFoundError}.
+   - The except body assigns to a self.<attr> (directly or via nested try).
+
+ Pre-Phase 12 baseline: 2. Post-Phase 12 baseline: 0.
+ """
+ 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]
+ unclear = [f for f in gui2.get("findings", []) if f.get("category") == "UNCLEAR"]
+ assert len(unclear) == 0, (
+  f"Phase 12 invariant: expected 0 UNCLEAR sites in src/gui_2.py "
+  f"(post-Phase 12 baseline; the 2 lazy-loading sentinel fallback sites "
+  f"in _LazyModule._resolve reclassified as INTERNAL_COMPLIANT); "
+  f"found {len(unclear)}. "
+  f"Lines: {[f.get('line') for f in unclear]}"
+ )
+
+
+def test_phase_12_invariant_l65_l69_reclassified():
+ """
+ Phase 12 invariant: the 2 lazy-loading sentinel fallback sites at L65 and
+ L69 in src/gui_2.py (the _LazyModule._resolve method) are no longer UNCLEAR.
+
+ The heuristic reclassifies except sites in methods named
+ _resolve/_load/_get/_try_load that fall back to a documented sentinel
+ class instance as INTERNAL_COMPLIANT. The audit must NOT report the
+ _LazyModule._resolve sites (L65, L69) as UNCLEAR after Phase 12.
+
+ Note: the line numbers may shift with future edits to src/gui_2.py.
+ This test scans ALL gui_2.py findings and asserts that no finding in
+ the _LazyModule._resolve method context is UNCLEAR.
+ """
+ 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]
+ unclear_in_resolve = [
+  f for f in gui2.get("findings", [])
+  if f.get("category") == "UNCLEAR"
+  and f.get("context") == "_resolve"
+ ]
+ assert len(unclear_in_resolve) == 0, (
+  f"Phase 12 invariant: expected 0 UNCLEAR findings in "
+  f"_LazyModule._resolve method context; found {len(unclear_in_resolve)}. "
+  f"Sites: {[(f.get('line'), f.get('context'), f.get('snippet')) for f in unclear_in_resolve]}"
+ )