test: check pinned source manifests against their own commits

Historical-evidence pins (dfg_re100 / jet_circle_cv / refined_dfg manifests)
now compare each recorded digest with the file at the recorded commit, read
with git, instead of with today's working tree. Missing history (no git,
shallow clone, installed copy) raises HistoryUnavailable and the test is
reported as skipped with that reason, never passed. Receipt/plan logic tests
take the selected manifest directly, so their assertions run again; the
pinned modes' mismatch rejections stay as negative controls.

V1 (run_jet_circle_cv) keeps its pinned mode and gains --current-checkout:
it records HEAD, the src tree and per-file hashes labelled as current
checkout, never as the frozen qualification, and requires a clean tree.

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

tests/unit/test_re100.py

@@ -67,8 +67,12 @@ def test_production_unmodified():
         (ROOT / "tests/validation/data/dfg_re100/source_manifest.json").read_text()
     )
     assert m["commit"] == h.PIN
-    for name, digest in m["production_sha256"].items():
-        assert hashlib.sha256((ROOT / name).read_bytes()).hexdigest() == digest, name
+    from source_provenance import HistoryUnavailable, historical_sha256
+    try:  # the manifest certifies its own commit, not today's working tree
+        actual = historical_sha256(ROOT, m["commit"], m["production_sha256"])
+    except HistoryUnavailable as error:
+        pytest.skip(f"historical integrity NOT checked: {error}")
+    assert actual == m["production_sha256"]
 
 
 def test_reference():