fix: handle non-ASCII challenge nonces without TypeError

CHANGELOG.md

@@ -11,6 +11,8 @@ Format: [Semantic Versioning](https://semver.org/). Spec versions follow `MAJOR.
 
 ## [Unreleased]
 
+- Compare challenge nonces as UTF-8 bytes so non-ASCII mismatches raise the documented ValueError instead of TypeError (#381). Matching strings remain accepted without Unicode normalization. Invalid non-string expected_nonce settings raise a clear ValueError. Reported by @chernistry; follow-up review by @lywinged.
+
 - Report revocation bundles without an RFC 8785 form as `unverified_for_revocation`
   with cause `bundle_malformed`, while continuing record verification (#382).
   The direct bundle-digest API still refuses such input. Reported by @chernistry.

src/agentrust_trace/sign.py

@@ -795,8 +795,12 @@ def verify_record(
 
     # Freshness: bind to a caller-supplied nonce when provided.
     if expected_nonce is not None:
+        if not isinstance(expected_nonce, str):
+            raise ValueError("expected_nonce must be a string")
         actual_nonce = record.get("runtime", {}).get("nonce")
-        if not isinstance(actual_nonce, str) or not compare_digest(actual_nonce, expected_nonce):
+        if not isinstance(actual_nonce, str) or not compare_digest(
+            actual_nonce.encode("utf-8"), expected_nonce.encode("utf-8")
+        ):
             raise ValueError("record runtime.nonce does not match expected_nonce")
 
     # Canonical bytes: record without "signature" key

tests/test_sign.py

@@ -1,6 +1,7 @@
 """Tests for agentrust_trace.sign."""
 
 import base64
+import hmac
 import json
 import time
 
@@ -1186,3 +1187,61 @@ def test_the_guards_do_not_refuse_what_they_should_accept():
 
     jwk_thumbprint(key_to_jwk(key))
     verify_record(record, key_to_jwk(key))
+
+
+@pytest.mark.parametrize("nonce", ["abc123", "n\u00f8nce", "\U0001f512"])
+def test_verify_record_nonce_unicode_match(nonce):
+    key = generate_key()
+    record = _fresh_record()
+    record["runtime"]["nonce"] = nonce
+    signed = sign_record(record, key)
+    verify_record(signed, key_to_jwk(key), expected_nonce=nonce)
+
+
+@pytest.mark.parametrize(
+    ("actual", "expected"),
+    [
+        ("wrong", "abc123"),
+        ("n\u00f8nce", "a-nonce-value"),
+        ("a-nonce-value", "n\u00f8nce"),
+        ("\U0001f512", "\U0001f513"),
+        ("\u00e9", "e\u0301"),
+    ],
+)
+def test_verify_record_nonce_unicode_mismatch(actual, expected):
+    key = generate_key()
+    record = _fresh_record()
+    record["runtime"]["nonce"] = actual
+    signed = sign_record(record, key)
+    with pytest.raises(ValueError, match="record runtime.nonce does not match expected_nonce"):
+        verify_record(signed, key_to_jwk(key), expected_nonce=expected)
+
+
+@pytest.mark.parametrize("expected", [b"a-nonce-value", 123, [], True, {}])
+def test_verify_record_rejects_invalid_expected_nonce_configuration(expected):
+    key = generate_key()
+    record = _fresh_record()
+    record["runtime"]["nonce"] = "a-nonce-value"
+    signed = sign_record(record, key)
+    with pytest.raises(ValueError, match="^expected_nonce must be a string$"):
+        verify_record(signed, key_to_jwk(key), expected_nonce=expected)
+
+
+def test_nonce_verdict_uses_compare_digest_result(monkeypatch):
+    key = generate_key()
+    record = _fresh_record()
+    record["runtime"]["nonce"] = "n\u00f8nce"
+    signed = sign_record(record, key)
+    real_compare = hmac.compare_digest
+    seen = []
+
+    def refuse_nonce(a, b):
+        if isinstance(a, bytes) and isinstance(b, bytes):
+            seen.append((a, b))
+            return False
+        return real_compare(a, b)
+
+    monkeypatch.setattr(hmac, "compare_digest", refuse_nonce)
+    with pytest.raises(ValueError, match="record runtime.nonce does not match expected_nonce"):
+        verify_record(signed, key_to_jwk(key), expected_nonce="n\u00f8nce")
+    assert seen == [("n\u00f8nce".encode("utf-8"), "n\u00f8nce".encode("utf-8"))]