MessagePack [Key("...")]-keyed contracts reject unknown fields, so request
DTOs that omit BaseRequest's envelope (viewer_id, steam_id,
steam_session_ticket) fail deserialization on the real msgpack wire path.
Routing smoke + JSON-direct tests didn't catch this because S.T.J. tolerates
extra keys and the routing smoke uses ValidBaseRequestJson, but anything
sent via the actual client encrypted=True path threw
MessagePackSerializationException.
Fix: every Arena*Request now inherits BaseRequest. Also updates the JSON
controller tests + e2e to include the envelope so the [ApiController]
auto-400 validation passes.
Discovered via /arena_colosseum/get_fee_info crash on the in-game arena
screen.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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