Contracts: Add multi-campaign rewards multiplier with campaign ID linkage

[CelestinaBeing]

Summary

The rewards contract supports campaign multipliers via campaign_multiplier(campaign_id), but the campaign_id is a u64 with no on-chain linkage to an actual campaign contract address. This loose coupling means any caller can claim any campaign_id multiplier without proving they are associated with that campaign.

Problem

In contracts/rewards/src/lib.rs:159:

pub fn campaign_multiplier(env: Env, campaign_id: u64) -> u32 {

• campaign_id is arbitrary; there is no validation that it corresponds to a real deployed campaign
• A caller could abuse a high-multiplier campaign_id to credit themselves at an inflated rate
• No on-chain record linking campaign contract address ↔ campaign_id

Acceptance Criteria

• Change campaign_id type from u64 to Address (the actual campaign contract address)
• set_campaign_multiplier(admin, campaign_contract: Address, multiplier_bps) now takes an Address
• credit_for_campaign(from, user, campaign_contract: Address, base_amount) — validate that campaign_contract.is_active() returns true before applying multiplier (cross-contract read)
• Emit updated events with Address instead of u64 campaign_id
• Update all tests to use Address-typed campaign identifiers
• Update frontend/src/stellar.js accordingly
• Add migration note in CHANGELOG.md (breaking change in campaign_id type)

References

• contracts/rewards/src/lib.rs:139-165
• contracts/campaign/src/lib.rs:339 — is_active()

[uboho-prog]

@uboho-prog has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

I can work on this m, kindly assign

ℹ️ Repo Maintainers: To accept this application, review their application or assign @uboho-prog to this issue.

[presidojay1]

@presidojay1 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

I would like to work to on this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @presidojay1 to this issue.

[drips-wave]

Congratulations, @presidojay1! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

🧑‍💻 @presidojay1: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

Warning

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊