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_validation_source_provenance.py

@@ -8,17 +8,21 @@ import sys
 
 ROOT = Path(__file__).resolve().parents[2]
 sys.path.insert(0, str(ROOT / "tests/validation"))
-from source_provenance import checkout_provenance
+import pytest
+from source_provenance import (HistoryUnavailable, checkout_provenance, historical_sha256,
+                               historical_tree)
 import re100_helpers
 import run_jet_circle_cv
 
 ORIGIN = "47b05bc8abfc957fe876b0c63bdb386e3c6cbaa5"
 
 
-def test_manifests_cover_current_source_and_preserve_origin():
-    names = subprocess.check_output(
-        ["git", "-C", str(ROOT), "ls-files", "src"], text=True
-    ).splitlines()
+def test_manifests_match_their_recorded_source_and_preserve_origin():
+    """Historical evidence integrity: each manifest describes the tree of its own commit."""
+    try:
+        names = historical_tree(ROOT, ORIGIN)
+    except HistoryUnavailable as error:
+        pytest.skip(f"historical integrity NOT checked: {error}")
     for group, hashes_key, revision_key in (
         ("dfg_re100", "production_sha256", "commit"),
         ("jet_circle_cv", "files", "revision"),
@@ -36,10 +40,7 @@ def test_manifests_cover_current_source_and_preserve_origin():
             == "d79e3f6f0a424f5bcc3a1a6d610313e49daf97a2"
         )
         assert "not inherited from d79" in manifest["experiment"]
-        for name, expected in manifest[hashes_key].items():
-            assert (
-                hashlib.sha256((ROOT / name).read_bytes()).hexdigest() == expected
-            ), name
+        assert historical_sha256(ROOT, ORIGIN, manifest[hashes_key]) == manifest[hashes_key]
     assert re100_helpers.PIN == run_jet_circle_cv.PIN == ORIGIN
 
 
@@ -72,3 +73,18 @@ def test_runtime_checkout_identity_is_separate_from_source_origin(tmp_path):
     assert checkout_provenance(tmp_path) == dict(
         checkout_revision=expected, checkout_dirty=True
     )
+
+
+def test_historical_check_rejects_tampering_and_reports_missing_history(tmp_path):
+    with pytest.raises(HistoryUnavailable):
+        historical_sha256(tmp_path, ORIGIN, ["src/x.py"])  # not a repository
+    with pytest.raises(HistoryUnavailable):
+        historical_sha256(ROOT, "0" * 40, ["src/x.py"])  # commit absent
+    manifest = json.loads(
+        (ROOT / "tests/validation/data/dfg_re100/source_manifest.json").read_text())
+    name = sorted(manifest["production_sha256"])[0]
+    try:
+        actual = historical_sha256(ROOT, ORIGIN, [name])
+    except HistoryUnavailable as error:
+        pytest.skip(f"historical integrity NOT checked: {error}")
+    assert actual != {name: "0" * 64}  # a tampered digest would not match