diff --git a/conformance/.clusterfuzzlite/fuzz_receipt.py b/conformance/.clusterfuzzlite/fuzz_receipt.py
index 2e9573ce..5040eecd 100755
--- a/conformance/.clusterfuzzlite/fuzz_receipt.py
+++ b/conformance/.clusterfuzzlite/fuzz_receipt.py
@@ -25,6 +25,8 @@
     from trace_tests.inclusion import (
         InclusionError,
         canonical_claim_bytes,
+        parse_entry,
+        parse_proof,
         parse_receipt,
         verify_inclusion,
     )
@@ -121,8 +123,12 @@ def TestOneInput(data: bytes) -> None:
     findings = tr_anc.check(claim, receipt=receipt, entry=_ENTRY)
     if any(f.code == "TR-ANC-002" and f.passed() for f in findings):
         assert claim is _CLAIMS[_TARGET], f"inclusion proven for the wrong claim: {receipt!r}"
-        root = parse_receipt(receipt)[3]
+        index, path, _, _ = parse_proof(receipt)
+        root, count, _, _ = parse_entry(_ENTRY)
         assert root == _ROOT, f"inclusion proven under another root: {receipt!r}"
+        assert verify_inclusion(claim, index, path, count, root), (
+            f"inclusion not reproduced against the supplied entry: {receipt!r}"
+        )
 
 
 def main() -> None:
diff --git a/conformance/tests/test_fuzz_receipt.py b/conformance/tests/test_fuzz_receipt.py
new file mode 100644
index 00000000..be010b29
--- /dev/null
+++ b/conformance/tests/test_fuzz_receipt.py
@@ -0,0 +1,58 @@
+"""Deterministic receipt-harness regressions without requiring Atheris."""
+
+import contextlib
+import json
+import runpy
+import sys
+import types
+from pathlib import Path
+
+import pytest
+
+
+@pytest.fixture
+def harness(monkeypatch):
+    # Exercise the real fuzz callback's raw-JSON branch; only instrumentation
+    # and byte selection are replaced, not the parser, verifier, or assertions.
+    class DataProvider:
+        def __init__(self, data):
+            self.data = data
+
+        def ConsumeIntInRange(self, lower, upper):
+            return 3  # The genuine fixture's target claim.
+
+        def ConsumeBool(self):
+            return False
+
+        def remaining_bytes(self):
+            return len(self.data)
+
+        def ConsumeBytes(self, length):
+            return self.data[:length]
+
+    stub = types.ModuleType("atheris")
+    stub.instrument_imports = contextlib.nullcontext
+    stub.FuzzedDataProvider = DataProvider
+    monkeypatch.setitem(sys.modules, "atheris", stub)
+    path = Path(__file__).parents[1] / ".clusterfuzzlite" / "fuzz_receipt.py"
+    return runpy.run_path(str(path))
+
+
+@pytest.mark.parametrize(
+    "omitted",
+    [(), ("leaf_count",), ("merkle_root",), ("leaf_count", "merkle_root")],
+)
+def test_pass_oracle_accepts_entry_backed_proofs(harness, omitted):
+    receipt = {k: v for k, v in harness["_RECEIPT"].items() if k not in omitted}
+    claim = harness["_CLAIMS"][harness["_TARGET"]]
+    findings = harness["tr_anc"].check(claim, receipt=receipt, entry=harness["_ENTRY"])
+    assert any(f.code == "TR-ANC-002" and f.passed() for f in findings)
+    harness["TestOneInput"](json.dumps(receipt).encode())
+
+
+def test_pass_oracle_independently_replays_proof(harness, monkeypatch):
+    receipt = {"leaf_index": harness["_TARGET"], "audit_path": []}
+    fake_pass = types.SimpleNamespace(code="TR-ANC-002", passed=lambda: True)
+    monkeypatch.setattr(harness["tr_anc"], "check", lambda *a, **kw: [fake_pass])
+    with pytest.raises(AssertionError, match="not reproduced against the supplied entry"):
+        harness["TestOneInput"](json.dumps(receipt).encode())