test: shear-wave modal-extinction handling; TG mock verify_source flow arg

- shear_wave.fit_rate: finite late R=0 returns rate_fit_valid=false with
  null fit quantities (no clipping, no invented rate); own screens and
  budgets treat it as a failure (CONTROL_SCREEN_FAIL / refined FAIL),
  other finite metrics retained, JSON-safe.
- test_projected_pairs: dry-run/execution mocks expect the explicit
  'taylor_green' flow argument now passed to verify_source.
- run_case: SHEAR_WAVE_SHA256 repinned; extinction test added.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/validation/taylor_green/test_shear_wave.py

@@ -4,6 +4,7 @@ Run from this directory with PYTHONPATH=<checkout>/src (same as test_oracle.py).
 """
 
 import hashlib
+import json
 import math
 import unittest
 from pathlib import Path
@@ -286,6 +287,32 @@ class AssessTests(unittest.TestCase):
         with self.assertRaises(ValueError):
             sw.assess(base, fine, [record(128, 2, rows_for(128)), record(128, 2, rows_for(128))])
 
+    def test_modal_extinction_is_a_failure_not_malformed(self):
+        def extinct(rows):
+            for row in rows[1:]:
+                row.update(a_hat=0.0, b_hat=0.0, modal_amplitude=0.0, amplitude_ratio=0.0,
+                           amplitude_error=-1.0)
+            return rows
+        base = record(128, 1, rows_for(128))
+        fine = record(256, 1, rows_for(256))
+        refined = record(128, 2, extinct(rows_for(128)))
+        report = sw.assess(base, fine, [refined])
+        self.assertEqual(report["status"], "FAIL")
+        own = report["refined"]["constant"]
+        self.assertTrue(own["valid"])
+        self.assertFalse(own["rate_fit_valid"])
+        self.assertIsNone(own["rate_error"])
+        self.assertIsNone(own["control_ratios"]["root"]["rate_error"])
+        self.assertFalse(own["own_screens_pass"] or own["controlled_pass"] or own["budget_pass"])
+        self.assertEqual(own["residual_l2"], 1e-4)  # other finite metrics retained
+        json.loads(json.dumps(report, allow_nan=False))
+        control = sw.assess(record(128, 1, extinct(rows_for(128))), fine,
+                            [record(128, 2, rows_for(128))])
+        self.assertEqual(control["status"], "CONTROL_SCREEN_FAIL")
+        self.assertIsNone(control["refined"]["constant"]["budget"]["rate_error"])
+        self.assertFalse(control["refined"]["constant"]["controlled_pass"])
+        json.loads(json.dumps(control, allow_nan=False))
+
     def test_wrong_shapes(self):
         base = record(128, 1, rows_for(128))
         fine = record(256, 1, rows_for(256))