New CGD corporate action details on NTA activity events

Broker API

Adds the OpcaCGDActivityV2 schema and includes it as a new variant in the ActivityV2DetailNTA oneOf. Capital Gain Distribution corporate action transactions now appear with their own detail payload on non-trade activity (NTA) events.

Affected Endpoints

• GET /v2beta1/events/activities
• GET /v2beta1/accounts/{account_id}/events/activities/{event_id}