Contracts: Add cross-contract integration — campaign auto-credits rewards on registration

[CelestinaBeing]

Summary

Currently the campaign and rewards contracts are independent — registering in a campaign does not automatically credit the participant with rewards. Operators must manually batch-credit participants after the fact. For a seamless user experience and trustless reward distribution, the campaign contract should optionally invoke the rewards contract to credit a registration bonus upon successful registration.

Problem

There is no cross-contract call flow:

• Campaign contract does not know the rewards contract address
• Registration does not trigger any credit
• Operators must manually call batch_credit after inspecting registration events

Acceptance Criteria

• Add optional rewards_contract: Option<Address> to campaign contract instance storage
• Add set_rewards_contract(admin, nonce, rewards_contract)) admin function to configure the linked rewards contract
• Add registration_bonus: u64 field (admin-configurable, default 0 = no auto-credit)
• In register(): if rewards_contract is set and registration_bonus > 0, call rewards.credit(campaign_admin, participant, bonus) via cross-contract invocation
• Cross-contract call is optional — if not configured, registration proceeds as today
• Add integration test: register participant → assert rewards balance increased by bonus
• Handle cross-contract call failure gracefully (registration still succeeds, emit a credit_failed event)
• Update docs/ARCHITECTURE_OVERVIEW.md with the new cross-contract flow

References

• contracts/campaign/src/lib.rs
• contracts/rewards/src/lib.rs
• Soroban cross-contract calls

[shaaibu7]

@shaaibu7 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

can i work on this

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[favour-GL]

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

Hi maintainer,

Can I work on this issue?

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