fix(thread): handle notification.mark_unread event

[TabishRiazBajwa]

Summary

Fixes #3076

Thread currently subscribes to message.read events to keep its read state up to date, but never subscribes to notification.mark_unread events. This means that when a user marks a thread as unread, the Thread's local state never reflects it — unreadMessageCount stays stale until the thread is reloaded.

Root cause

Channel already has a working handler for notification.mark_unread (see channel.ts), and Thread already has all the state infrastructure needed (ThreadUserReadState with unreadMessageCount, lastReadAt, lastReadMessageId) — it was just never wired up to this event.

Changes

• Added subscribeRepliesMarkUnread() to Thread, following the same .on() + filter pattern as the existing subscribeRepliesRead()
• Registered the new subscription in registerSubscriptions()
• Added 3 new test cases in threads.test.ts:
  • Ignores events from other threads (filtered by parent_message_id)
  • Ignores events for other users (only updates the current user's state)
  • Correctly updates unreadMessageCount, lastReadAt, and lastReadMessageId for the current user

Testing

All existing tests in threads.test.ts pass (87/87), including the 3 new ones added for this fix.

Notes

• Did not add first_unread_message_id tracking since ThreadUserReadState doesn't currently have an equivalent field (unlike ChannelState) — happy to add this in a follow-up if desired.
• Did not call messageReceiptsTracker, consistent with the existing subscribeRepliesRead() handler, since thread delivery receipts aren't supported yet.

CLA

• I have signed the Stream CLA (required).
• Code changes are tested

Description of the changes, What, Why and How?

Changelog