Automatically activate joined contest

[magnified103]

Motivation

The service allows a user to have multiple ContestParticipation records, but only one participation can be active at any time, determined by profile.current_contest.

When a user userX joins two contests (contestA then contestB), the following occurs:

1. Create ContestParticipation(contestA, userX) → partA
2. Set userX.current_contest = partA
3. Create ContestParticipation(contestB, userX) → partB
4. Set userX.current_contest = partB

To submit code for a contest problem, userX.current_contest must reference the participation associated with that contest.

As a result, after joining contestB, userX can no longer submit solutions to contestA unless they explicitly “join” contestA again, which only serves to reset:

• userX.current_contest = partA

This behavior is unintuitive and creates unnecessary user friction.

Proposed Solution (Temporary)

As a temporary mitigation, when a user accesses a contest page, the service should:

• Look up an existing ContestParticipation for the (user, contest) pair.
• If found, automatically set userX.current_contest to that participation.

This removes the need for users to manually re-join a contest solely to submit solutions.