Nothing reads it anymore — frontend uses message.call, CallMessageBuilder
uses call.message (the FK), and the jsonb fallback finder was dead code
(call.message_id is always linked immediately after message creation, in
the same transaction).
New voice_call messages are now created with blank content_attributes.
Existing rows keep their legacy payload; nothing reads it, so it's inert.
Safe to backfill with `Message.voice_calls.update_all(content_attributes: {})`
if you want a tidy table.
Muhsin
98ba6e5200