[FEAT] Implement Emergency Pause (Circuit Breaker) Functionality

[Queenode]

🟡 Priority: High
Difficulty: Hard
Estimated Effort: 2-3 days
Relevant Files: contracts/src/lib.rs
Labels: enhancement, priority:high, security

Requirements

1. Pausable State

   • Add DataKey::IsPaused to instance storage (boolean, defaults to false).
   • Add pub fn pause(env: Env) and pub fn unpause(env: Env) functions.
   • Only the Admin can call pause or unpause.

2. Function Modifiers

   • In contribute(), payout(), add_member(), and reset_cycle(), check IsPaused.
   • If true, panic with "Contract is paused for emergency".

3. Emergency Withdraw (Escape Hatch)

   • Add pub fn emergency_withdraw(env: Env) callable ONLY when the contract is paused.
   • Only members can call it.
   • It allows a member to withdraw exactly what they have contributed in the current active cycle.
   • This provides a trustless exit if the admin abandons the group or a bug is discovered.
   • It must update their Contributions state and clear HasContributedThisCycle.

4. State Integrity during Pause

   • The escape hatch must not allow draining more funds than the member put in.
   • If a member uses emergency_withdraw, the CycleMemberCount or CurrentCycleContributions counters must be decremented to keep the pool math valid if the contract is ever unpaused.

5. Testing

   • Unit test: Admin pauses, contributions fail.
   • Unit test: Admin unpauses, contributions succeed.
   • Unit test: Non-admin tries to pause (panics).
   • Integration test: Pause -> Member executes emergency withdraw -> Verify balance -> Unpause -> Contract math still works for remaining members.
   • Target: >90% coverage on pausable flows.

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[OluRemiFour]

Hi Maintainer,
Interested in working on this issue. I'll implement the requested changes and ensure everything is properly tested before submission.

[Muhamadmust]

Hi maintainer
I have reviewed this issue and would love to work on it, PR 2days