test: fix shear-wave review findings (runner finiteness, source pin, contract)

- run_case: finite_row accepts list diagnostics; sample() shared by sample
  and READY paths; verify_source pins shear_wave.py path+SHA256 for
  --flow shear_wave (default TG flow unchanged, does not import it).
- assess_shear_wave.py: fixed N128 four-case contract and 4-JSON CLI,
  reusing assess_projected_pairs provenance/build/workload/time checks plus
  shear metadata; missing/duplicate/mixed/extra records -> INVALID_SET.
- tests: mocked refined runner sample (list diagnostics, NaN, TG unchanged),
  contract pass + reproduced false-pass mutations, divergence check uses
  analytic E.k=0 and a derived h^2 truncation + roundoff bound with
  h-halving scaling instead of a fixed 1e-12.

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

tests/validation/taylor_green/run_case.py

@@ -18,6 +18,7 @@ SOURCE_SHA256 = "a5dbfd804befce868067d79a23e5fd47dce7f505b3f9b1bb2145fb57cb5f217
 BUILD_CAPTURE_SHA256 = "3dbaa6547cb0a4cb1541054f3b64ad8b6e18cc70527ac6166e56b944e9bd464a"
 REFERENCE_HARNESS = "11901a7f77557a901e017a171eeae1758d584fa5"
 INITIALIZATION = "physical FP64 equilibrium G at actual cell centers; rho=1+3p"
+SHEAR_WAVE_SHA256 = "49ab589d15d964d38ed90a49758e159c67a516191c7501c19fe2732e19742395"
 
 
 def flow_functions(flow="taylor_green"):
@@ -30,6 +31,19 @@ def flow_functions(flow="taylor_green"):
     raise ValueError(f"unknown flow {flow!r}")
 
 
+def finite_row(row):
+    """Every scalar or list-valued diagnostic is finite (TG rows are all scalars)."""
+    return all(np.isfinite(np.asarray(value, dtype=float)).all() for value in row.values())
+
+
+def sample(run, masks, step, n, viscosity, initial_mass, metrics, depth, label="sample"):
+    arrays = (run.download(),) if depth == 1 else run.download()
+    row = metrics(arrays, masks, step, n, viscosity, initial_mass)
+    if not finite_row(row):
+        raise FloatingPointError(f"nonfinite {label} diagnostics")
+    return row
+
+
 def sample_steps(n, early_pressure=False):
     """Root synchronization steps; early ladder matches the 707afe6 diagnostic."""
     main = [round(tstar * n / U) for tstar in TIMES]
@@ -74,7 +88,7 @@ def provenance(repo):
     )
 
 
-def verify_source(repo, revision):
+def verify_source(repo, revision, flow="taylor_green"):
     """Exact clean harness commit, fixed production tree, and reviewed capture helper."""
     import oracle
     from tests.validation.multigrid import check_projected_pairs as gate
@@ -93,6 +107,13 @@ def verify_source(repo, revision):
     if result["source_tree_sha256"] != SOURCE_SHA256:
         raise RuntimeError("Wrong numerical source fingerprint")
     result["build_capture_sha256"] = BUILD_CAPTURE_SHA256
+    if flow == "shear_wave":
+        import shear_wave
+        module = harness / "shear_wave.py"
+        if (Path(shear_wave.__file__).resolve() != module
+                or hashlib.sha256(module.read_bytes()).hexdigest() != SHEAR_WAVE_SHA256):
+            raise RuntimeError("Wrong shear_wave module checkout or content")
+        result["shear_wave_sha256"] = SHEAR_WAVE_SHA256
     return result
 
 
@@ -175,7 +196,7 @@ def main():
         p.error("--run-gpu and exactly one explicit CUDA_VISIBLE_DEVICES are required")
     repo = args.repo.resolve()
     sys.path[:0] = [str(repo / "src"), str(repo)]
-    source = verify_source(repo, args.expected_revision)
+    source = verify_source(repo, args.expected_revision, args.flow)
     runtime = runtime_source(repo)
     if args.dry_run:
         print(json.dumps(dict(source=source, runtime_source=runtime, dry_run=True)))
@@ -267,10 +288,8 @@ def main():
             initial_mass = None
             for step in sorted(set(main_steps + early_steps)):
                 run.step(step - run.step_count)
-                arrays = (run.download(),) if args.depth == 1 else run.download()
-                row = metrics(arrays, masks, step, args.n, cfg.viscosity, initial_mass)
-                if not all(np.isfinite(value) for value in row.values()):
-                    raise FloatingPointError("nonfinite sample diagnostics")
+                row = sample(run, masks, step, args.n, cfg.viscosity, initial_mass,
+                             metrics, args.depth)
                 row["step"] = step
                 if initial_mass is None:
                     initial_mass = row["mass"]
@@ -297,10 +316,8 @@ def main():
                     # Exercise real kernels/halos/transfers on every level before READY.
                     # This is the first measured trajectory step, not discarded warmup.
                     run.step(1)
-                    probe = (run.download(),) if args.depth == 1 else run.download()
-                    probe_metrics = metrics(probe, masks, 1, args.n, cfg.viscosity, initial_mass)
-                    if not all(np.isfinite(value) for value in probe_metrics.values()):
-                        raise FloatingPointError("nonfinite READY diagnostics")
+                    sample(run, masks, 1, args.n, cfg.viscosity, initial_mass,
+                           metrics, args.depth, "READY")
                     report["ready_after_step"] = 1
                     save()
                     print(