Watchlist subscriptions

Ideas/proposal

Why
To help organize timely admin attention on articles which need it. And to help users to keep track of articles that they are interested in.

What
Users may subscribe their account to a special watchlist channel. When an article is pushed onto the channel it will be added to the watchlists of all subscribing users. Users will also receive a notification of additions, similar to the 'you have messages' notification.

Special pages

 * a list of channels with subscribe/unsubscribe interface
 * a method for creating and managing channels
 * a convenient way to add pages to a channel (from a toolbox link?)

Tables
watchchannels:
 * wc_id
 * wc_restriction [empty, or list of groups who can push?]

watchchannel_users
 * wcu_user -> user_id
 * wcu_channel -> wc_id
 * wcu_update (timestamp)

May also want to add a generalizable notification infrastructure:

notifications
 * n_user -> user_id
 * n_timestamp
 * n_expiry
 * n_summary (comment-formatted)
 * n_text (wikitext-formatted?)