Rolling campaigns with rank persistence (v1.1)

[alexanderkoh]

Description

Users who kept LP through the vesting period of campaign N should get rank priority in campaign N+1 for the same pool. This creates a loyalty flywheel — long-term LPs get structural advantages.

Design (from spec)

• Opt-in with rank bonus: Users must explicitly join campaign N+1, but if they had a position in campaign N (and fully vested), they get placed before all new joiners
• Campaign struct already links via pool_address — query previous campaigns for the same pool
• UserPos is NOT deleted after claim (weight set to 0) — past positions are queryable

Implementation approach

1. Add prev_campaign: Option<u32> to Campaign struct
2. On create_campaign, check for ended campaigns on the same pool and link
3. On join_campaign, check if user had a position in the previous campaign
4. If yes, assign rank priority (e.g., rank 1-N for returning users, N+1 onwards for new)

Why deferred

Decided during design phase to ship v1 without this. The contract already preserves the data needed — adding this doesn't require migration.