LINEEventConverter.target2yiri() built Friend.id/Group.id from
event.message.id, which is unique per message. Every incoming message
therefore mapped to a new session key, so LINE users and groups lost
conversation context on every turn.
Use event.source.user_id/group_id/room_id instead, matching the stable
identifiers other adapters (e.g. Telegram) use for session identity.
Falls back to the group/room id when user_id is absent, per LINE's
documented behavior for some group/room members.
leonoxo