fix(intent-bridge): preserve canonicalization error classification

src/agentrust_trace/intent_bridge.py

@@ -240,20 +240,17 @@ def verify_bridge(
         if not isinstance(transcript, dict) or set(transcript) != {"before", "after"}:
             raise AuthorizationMismatch("a full before/after transcript is required")
         before = transcript.get("before")
-        if not isinstance(before, dict) or not isinstance(before.get("tool_call"), dict):
+        before_call = before.get("tool_call") if isinstance(before, dict) else None
+        if not isinstance(before_call, dict):
             raise AuthorizationMismatch("transcript.before.tool_call does not match execution")
         # Host-language equality is not this bridge's identity relation. Python holds
-        # True == 1 and False == 0, nested objects included, so comparing the two call
-        # objects with != accepts a transcript whose call has different JCS bytes from
-        # the one the authorization digested (#317). Every other comparison in this
-        # function is over canonical bytes; so is this one.
-        try:
-            before_digest = digest_jcs(before["tool_call"])
-        except IntentBridgeError:
-            raise AuthorizationMismatch(
-                "transcript.before.tool_call does not match execution"
-            ) from None
-        if not compare_digest(before_digest, tool_call_digest):
+        # True == 1 and False == 0, nested objects included, so compare the exact RFC
+        # 8785 bytes instead. If either object has no canonical form, _jcs raises
+        # IntentBridgeError: that input cannot be evaluated, which is not a mismatch.
+        if not compare_digest(
+            _jcs(before_call, "transcript.before.tool_call"),
+            _jcs(tool_call, "tool_call"),
+        ):
             raise AuthorizationMismatch("transcript.before.tool_call does not match execution")
         if not isinstance(transcript.get("after"), dict):
             raise AuthorizationMismatch("transcript.after must contain the execution result")

tests/test_intent_bridge.py

@@ -355,3 +355,19 @@ def test_transcript_call_that_is_not_an_object_stays_an_authorization_mismatch(
             transcript={"before": {"tool_call": bad}, "after": {"status": "accepted"}},
             now=150,
         )
+
+@pytest.mark.parametrize("bad", [{"approved": 2**60}, {"approved": float("nan")}])
+def test_uncanonicalizable_transcript_call_is_intentbridgeerror_not_mismatch(
+    bad: dict,
+) -> None:
+    """An unrepresentable transcript call cannot be evaluated; it is not a mismatch."""
+    bridge, key, declaration, intent, args, tool_call, _ = _fixture()
+    transcript_call = {"name": "send_invoice", "arguments": bad}
+    with pytest.raises(IntentBridgeError, match="transcript.before.tool_call") as excinfo:
+        verify_bridge(
+            bridge, {**key_to_jwk(key), "kid": "key-7"}, declaration=declaration,
+            pic_intent_digest=intent, pic_args_digest=args, tool_call=tool_call,
+            transcript={"before": {"tool_call": transcript_call}, "after": {"status": "accepted"}},
+            now=150,
+        )
+    assert not isinstance(excinfo.value, AuthorizationMismatch)