fix: return None instead of raw invalid data in invalid_to_none

synth/protocol.py

@@ -35,7 +35,7 @@ def invalid_to_none(v: Any, handler: Callable[[Any], Any]) -> Any:
     try:
         return handler(v)
     except ValidationError:
-        return v
+        return None
 
 
 class Simulation(bt.Synapse):

tests/test_protocol.py

@@ -0,0 +1,52 @@
+from pydantic import ValidationError
+
+from synth.protocol import invalid_to_none
+
+
+def mock_handler(v):
+    """Simulates Pydantic validation that succeeds."""
+    if not isinstance(v, tuple):
+        raise ValidationError.from_exception_data(
+            title="test",
+            line_errors=[],
+        )
+    return v
+
+
+class TestInvalidToNone:
+    def test_valid_data_passes_through(self):
+        """Valid data should be returned as-is."""
+        valid = (1, [1.0, 2.0], [3.0, 4.0])
+        result = invalid_to_none(valid, mock_handler)
+        assert result == valid
+
+    def test_invalid_data_returns_none(self):
+        """Invalid data should return None, not the raw invalid value.
+
+        This was the bug: previously returned the raw invalid value `v`,
+        allowing malformed miner responses to bypass validation.
+
+        Example: a miner sends "garbage_string" as simulation_output.
+        Before fix: invalid_to_none returned "garbage_string"
+        After fix:  invalid_to_none returns None
+        """
+        result = invalid_to_none("not_a_tuple", mock_handler)
+        assert result is None, (
+            "invalid_to_none must return None for invalid data, "
+            "not the raw value"
+        )
+
+    def test_invalid_dict_returns_none(self):
+        """Malformed dict input should return None."""
+        result = invalid_to_none({"malicious": "data"}, mock_handler)
+        assert result is None
+
+    def test_invalid_list_returns_none(self):
+        """List instead of tuple should return None."""
+        result = invalid_to_none([1, 2, 3], mock_handler)
+        assert result is None
+
+    def test_none_input_returns_none(self):
+        """None input that fails validation should return None."""
+        result = invalid_to_none(None, mock_handler)
+        assert result is None