[we4sz]

Two fields that Slack sends on messages read through conversations.history and conversations.replies have no property on MessageEvent, the type SlackNet reads those messages into. I found them comparing real responses of both methods with MessageEvent. My app doesn't read them through a workaround today. This models them. It is one commit.

1. ParentUserId (parent_user_id), sent on the replies in a thread.
2. Subscribed (subscribed), sent on the parent message of a thread.

Compatibility

Additive only. The new properties default to null and false, and the message subtypes that inherit from MessageEvent get them too.

Testing

New MessageThreadTests: a reply with parent_user_id, a thread parent with subscribed, and a message outside a thread, in the style of MessageTeamTests (including that the fields no longer land in ExtraProperties). ./do test passes (786 tests).

Seen in a real response: subscribed in real conversations.history and conversations.replies responses, and parent_user_id in a real conversations.replies response.

Not verified: what they mean. The reference shows them only in the example responses of conversations.replies and "Retrieving messages" and never describes them, so the properties have no doc comment. Reading the examples, parent_user_id is the author of the thread's parent message and subscribed sits on the parent message next to reply_count. I also haven't run my app against a local pack of this branch.