Fix: Serialize each object at its outermost layer only

[wanderingnish]

Summary

Fix inconsistent Player serialization in team lists - objects now serialize at their outermost layer only

Problem

The serialize() function mixed integers and full Player dicts in team lists:

"team": [1, {"number": 3, "name": "PlayerThree", ...}, 5, 7]  ❌

Expected:

"team": [1, 3, 5, 7]  ✅

Root Cause

When serializing a list, objects from later in the list were serialized WITHIN earlier objects.

Example: In player list [P1, P2, P3, P4], P1 has {team: [P1, P3]}. When serializing P1's team, P3 would be fully serialized instead of using a hash value and letting P3 be serialized later in the outer list.

Solution

Two-pass approach for lists:

1. First pass: Mark all objects as seen (reserve for this layer)
2. Second pass: Recursively serialize each object; inner references to objects from
   outer layer will now use hash value.

Each object is fully serialized exactly once at its outermost layer.

Testing

Added 3 new tests in tests/test_serialize.py:

• test_players_are_dicts: Players serialize as full dict objects
• test_team_references_are_integers: Team lists contain only integers
• test_no_circular_references: No circular references in serialized data

All 24 tests pass (21 existing + 3 new)

Impact

• ✅ Consistent integer references across all contexts
• ✅ ~385KB smaller JSON output for 8-player games
• ✅ No breaking changes to public API

🤖 Initially generated with Claude Code, edited & verified manually.