=== Background
There will be an initial system-imposed limit of 1,000 articles per user-created reading lists for the sync service.
As such, there needs to be a suitable migration action for existing Reading list users with lists over that limit.
=== User story
As a power reading list user with lists of >1k articles, I want all my articles to be maintained when sync is enabled.
=== Proposed solution
- Move each additional 1-1K articles above the 1K limit of a list into a separate list
- Each additional list created will use the same name by appended with incrementing numbers (eg., a list called "Interesting" containing 2,001 articles will be split into 3 lists: "Interesting", "Interesting_1", "Interesting_2").
- A message will be shown to any user where this operation occurs that "There is a limit of 1000 articles per synced reading list. Existing lists with more than this limit have been split into multiple lists."
==== QA steps
// Pre-requisite: There is at least 1 reading list created that contains more than 1K articles. //
# Open to view reading lists and note that for at least one reading list, the number of articles exceeds 1K. For example a reading list called "Interesting" contains 2,001 articles
# Log in and opt-in to allow reading list sync
# Go to the reading list screen. It is **expected** that a message (see details in 'proposed solution') will be shown advising that lists with >1K have been split; and the "Interesting" list should now be shown as containing 1K articles, with 2 new reading lists created called "Interesting_1" and "Interesting_2", with 1,000, and 1 articles in them respectively.