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>

docs/validation/taylor_green.md

@@ -259,3 +259,24 @@ Run set: uniform N, uniform 2N, and refined depth-2 runs at root N.
 One flow, one phase and one rectangle, SRT only. The rectangle's vertical
 faces span 0.625 tangential periods and its horizontal faces 1.5, so this
 is not placement robustness. Two resolutions show a trend, not an order.
+
+### Receipt assessment and runner integrity
+
+- Fixed four-case N128 contract:
+  `python assess_shear_wave.py U128.json U256.json R128_constant.json R128_projected.json --output report.json --expected-revision <sha>`.
+  It reuses the shared provenance, build, workload and sample-time checks
+  from `assess_projected_pairs.py`, and adds shear metadata checks (flow,
+  mode, polarization, angle, phase, eps, limits, disabled early trace, and
+  pinned `shear_wave.py` hash).
+  - Missing, extra, duplicate or mixed-source records give `INVALID_SET`,
+    as does any failed shared check.
+  - Otherwise the result comes from `shear_wave.assess`, which separates
+    `INVALID_CONTROL` from `CONTROL_SCREEN_FAIL`.
+- `run_case.verify_source(..., flow="shear_wave")` requires the imported
+  `shear_wave.py` to be the selected harness file with the pinned
+  `SHEAR_WAVE_SHA256`. The default TG flow does not import it.
+- Sample and READY finiteness use `finite_row`, which accepts scalar and
+  list diagnostics. For TG's all-scalar rows it behaves the same as before.
+- Merge note: native 92b8afe adds a `scaled_n256` receipt block. When the
+  two are merged, keep both blocks and make `--flow shear_wave` and
+  `scaled_n256` mutually exclusive. Not merged here.