Fix IB ineligibility reason serialization (#4380)

Newer IB Gateway versions may return ineligibilityReasonList populated
with ibapi.ineligibility_reason.IneligibilityReason objects in
contractDetails. _serialize_for_json() only handled Decimal/Enum and
passed other objects through unchanged, so persisting the instrument
to a cache database (Redis/msgpack) raised:

    TypeError: Encoding objects of type
    <class 'ibapi.ineligibility_reason.IneligibilityReason'>
    is unsupported

_serialize_for_json() now checks primitive types first, then converts
arbitrary objects with __dict__ via vars() recursively (reusing the
existing dict branch), falling back to str() for anything else. Adds
a regression test that reproduces the original TypeError and verifies
the fix, and a RELEASES.md entry.

Author: xxxxxx-oss

RELEASES.md

@@ -65,6 +65,7 @@ releases as feedback arrives, before the final `2.0.0` release.
 - Fixed Tardis replay trades directory to `trades/` for catalog compatibility (#4373), thanks @AdvancedUno
 - Fixed Tardis replay bars directory to `bars/` for catalog compatibility (#4378), thanks @AdvancedUno
 - Fixed Hyperliquid `l2Book` resubscribe options and shared stream teardown (#4298)
+- Fixed Interactive Brokers `contract_details_to_dict` crash when `contractDetails.ineligibilityReasonList` contains non-serializable `IneligibilityReason` objects
 
 ### Internal Improvements
 - Improved core decimal deserialization to round fractional scales above 28 digits instead of erroring

nautilus_trader/adapters/interactive_brokers/parsing/instruments.py

@@ -1016,10 +1016,19 @@ def contract_details_to_dict(contract_details: IBContractDetails) -> dict:
 def _serialize_for_json(obj: object) -> object:
     """
     Recursively convert Decimal objects and Enum objects to JSON-serializable types.
+
+    Falls back to converting arbitrary objects (such as ibapi response types like
+    ``IneligibilityReason``) via ``vars()``, and to ``str()`` for anything else, so that
+    unexpected fields returned by newer IB Gateway versions do not break downstream
+    msgpack/JSON serialization (e.g. when persisting instruments to a cache database).
+
     """
     if obj is None:
         return None
 
+    if isinstance(obj, (str, int, float, bool)):
+        return obj
+
     if isinstance(obj, Decimal):
         return str(obj)
 
@@ -1032,7 +1041,10 @@ def _serialize_for_json(obj: object) -> object:
     if isinstance(obj, (list, tuple)):
         return [_serialize_for_json(item) for item in obj]
 
-    return obj
+    if hasattr(obj, "__dict__"):
+        return _serialize_for_json(vars(obj))
+
+    return str(obj)
 
 
 def _tick_size_to_precision(tick_size: float | Decimal) -> int:

tests/integration_tests/adapters/interactive_brokers/test_parsing.py

@@ -16,8 +16,10 @@
 import datetime
 from decimal import Decimal
 
+import msgspec
 import pandas as pd
 import pytest
+from ibapi.ineligibility_reason import IneligibilityReason
 
 from nautilus_trader.adapters.interactive_brokers.common import IBContract
 from nautilus_trader.adapters.interactive_brokers.common import IBContractDetails
@@ -36,6 +38,9 @@
 from nautilus_trader.adapters.interactive_brokers.parsing.instruments import VENUES_FUT
 from nautilus_trader.adapters.interactive_brokers.parsing.instruments import VENUES_OPT
 from nautilus_trader.adapters.interactive_brokers.parsing.instruments import _tick_size_to_precision
+from nautilus_trader.adapters.interactive_brokers.parsing.instruments import (
+    contract_details_to_dict,
+)
 from nautilus_trader.adapters.interactive_brokers.parsing.instruments import (
     expiry_timestring_to_datetime,
 )
@@ -643,3 +648,27 @@ def test_valid_magnifier(
     @pytest.mark.parametrize("price_magnifier", [None, 0, -1])
     def test_invalid_magnifier_returns_original(self, price_magnifier: int | None) -> None:
         assert nautilus_price_to_ib_price(50.0, price_magnifier) == 50.0
+
+
+def test_contract_details_to_dict_serializes_ineligibility_reason_objects() -> None:
+    # Arrange
+    # Newer IB Gateway versions may populate `ineligibilityReasonList` with
+    # `ibapi.ineligibility_reason.IneligibilityReason` objects, which are plain Python
+    # objects (not Decimal/Enum/dict/list/tuple) and previously passed through
+    # `_serialize_for_json` unchanged, breaking downstream msgpack/JSON serialization
+    # (e.g. when persisting the instrument to a cache database).
+    contract_details = IBTestContractStubs.aapl_equity_contract_details()
+    contract_details.ineligibilityReasonList = [
+        IneligibilityReason("200", "Not eligible for continuous trading"),
+    ]
+    ib_contract_details = IBContractDetails.from_contract_details(contract_details)
+
+    # Act
+    result = contract_details_to_dict(ib_contract_details)
+
+    # Assert
+    encoded = msgspec.msgpack.encode(result)
+    decoded = msgspec.msgpack.decode(encoded)
+    assert decoded["ineligibilityReasonList"] == [
+        {"id_": "200", "description": "Not eligible for continuous trading"},
+    ]