Feat/staked keys regression test

[Unclebaffa]

Summary

I have successfully implemented key staking functionality for the creator-keys contract to prevent selling of staked keys. Here's what was done:

✅ Implementation Complete (Commit 1)

File Modified: creator-keys/src/lib.rs

1. Added Storage Key: StakedBalance(Address, Address) to track staked keys per (creator, holder) pair

2. New Functions Implemented:

   • stake_keys() - Locks keys from being sold
   • unstake_keys() - Unlocks previously staked keys
   • get_staked_balance() - View staked amount
   • get_liquid_balance() - View sellable amount (total - staked)

3. Modified sell_key() Function:

   • Now checks liquid balance (total - staked) instead of just total balance
   • Reverts with InsufficientBalance if trying to sell more than liquid balance
   • Staked keys are protected from being sold

✅ Tests Complete (Commit 2)

File Created: creator-keys/tests/sell_requires_liquid_balance.rs

Three comprehensive test cases covering all acceptance criteria:

1. test_sell_reverts_when_attempting_to_use_staked_keys

   • ✅ Holder with 10 keys stakes 6, leaving 4 liquid
   • ✅ Attempt to sell 5 keys fails with InsufficientBalance

2. test_sell_succeeds_within_liquid_balance_limit

   • ✅ Selling exactly 4 liquid keys succeeds
   • ✅ Staked balance remains at 6

3. test_staked_balance_unchanged_after_sell_attempts

   • ✅ Staked balance unchanged after failed sell attempt
   • ✅ Staked balance unchanged after successful sells

✅ Code Formatting Summary

What Was Accomplished

1. Code Formatting ✅

• Ran cargo fmt to fix all formatting issues in both implementation and test files
• All Rust code now follows standard formatting conventions

2. Comprehensive Invariant Tests Added ✅

Created 14 comprehensive tests organized into three categories:

Core Protection Tests (3 tests):

• Verify all acceptance criteria from the requirements
• Test that staked keys cannot be sold
• Test that selling within liquid balance succeeds
• Verify staked balance remains unchanged

Invariant Tests (6 tests):

• invariant_liquid_equals_total_minus_staked - Mathematical correctness
• invariant_staked_never_exceeds_total - Boundary enforcement
• invariant_total_equals_liquid_plus_staked - Balance composition
• invariant_staking_preserves_total_balance - Total immutability
• invariant_sell_only_reduces_liquid_not_staked - Sell isolation
• invariant_staked_isolated_per_creator_holder_pair - Storage isolation

Edge Case Tests (5 tests):

• Zero amount staking/unstaking
• Insufficient balance scenarios
• Stake all/unstake all workflows
• Buy after staking behavior
• Partial unstake then sell

3. Seven Key Invariants Verified ✅

1. Liquid balance = Total balance - Staked balance
2. Staked balance ≤ Total balance
3. Sell operations only consume liquid balance
4. Stake operations only consume liquid balance
5. Total balance = Liquid balance + Staked balance
6. Staking/unstaking does not affect total balance
7. Staked balance is isolated per (creator, holder) pair

Files Modified/Created

1. creator-keys/src/lib.rs - Implementation (already committed)
2. creator-keys/tests/sell_requires_liquid_balance.rs - 14 comprehensive tests
3. STAKING_IMPLEMENTATION.md - Implementation documentation
4. TEST_SUMMARY.md - Test documentation

All Acceptance Criteria Met ✅

• Sell of 5 reverts when only 4 liquid keys available
• Sell of 4 succeeds using only liquid balance
• Staked balance unchanged after both attempts
• Code formatting verified and fixed
• Comprehensive invariant tests added

Testing Philosophy

The test suite follows a defense-in-depth approach:

• Core tests verify business requirements
• Invariant tests prevent mathematical bugs and regressions
• Edge case tests catch boundary condition failures

This ensures the implementation is not only correct today but remains correct through future modifications.

Closes #546