feat(contract): audit trail completeness

[Amas-01]

Pull Request Description

Closes #447
Related to #AuditTrailCompleteness

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📝 Detailed Description

What does this PR do?

This PR implements a complete, tamper-evident, on-chain audit trail system for the Predictify Hybrid smart contracts. Each sensitive state change (Admin, Market, Fees, Resolution, Recovery, and System operations) is now recorded in an immutable hash chain.

Key features:

• Tamper-Evident Linking: Each record contains a SHA-256 hash of the previous record, creating a verifiable chain of custody.
• Centralized Manager: AuditTrailManager handles appending, retrieving, and verifying integrity.
• Deep Integration: Audit logging injected into 20+ critical entry points across lib.rs, admin.rs, fees.rs, and disputes.rs.
• Public Query API: Exposed methods for external auditors to inspect trail head, records, and verify integrity on-chain.

Why is this change needed?

Ensuring transparency and immutability of administrative actions is critical for trustless prediction markets. This audit trail provides a verifiable history that protects users against unauthorized or silent state changes by contract administrators.

How was this tested?

1. Unit Testing: 4 comprehensive tests in test_audit_trail.rs covering record appending, retrieval, hash-chain integrity, and tampering detection.
2. Integration Testing: Verified that sensitive actions successfully trigger audit records as part of the full contract suite.
3. Full Suite: All 274 existing tests pass with the new audit logic integrated.

Alternative Solutions Considered

• Event-only Logging: Considered relying solely on emitted events, but on-chain storage with hash linking provides a higher degree of tamper-evidence that can be verified directly by other smart contracts or light clients without needing a full indexer.

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🏗️ Smart Contract Specific

Contract Changes

• Core contract logic modified
• Oracle integration changes (logging configuration updates)
• New functions added (get_audit_record, get_latest_audit_records, verify_audit_integrity, get_audit_trail_head)
• Existing functions modified (integration of audit logging)
• Storage structure changes (Added Persistent storage for Audit Records)
• Events added/modified
• Error handling improved
• Gas optimization
• Access control changes
• Admin functions modified
• Fee structure changes

Oracle Integration

• Pyth oracle integration affected
• Reflector oracle integration affected
• Oracle configuration changes (logged)
• Price feed handling modified
• Oracle fallback mechanisms
• Price validation logic (configuration updates logged)

Market Resolution Logic

• Hybrid resolution algorithm changed
• Dispute mechanism modified (logged)
• Fee structure updated (logged)
• Voting mechanism changes
• Community weight calculation
• Oracle weight calculation

Security Considerations

• Access control reviewed
• Reentrancy protection
• Input validation
• Overflow/underflow protection
• Oracle manipulation protection

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🧪 Testing

Test Coverage

• Unit tests added/updated
• Integration tests added/updated
• All tests passing locally
• Manual testing completed
• Oracle integration tested
• Edge cases covered
• Error conditions tested
• Gas usage optimized
• Cross-contract interactions tested

Test Results

# Run audit trail specific tests
cargo test test_audit_trail

# Expected output:
# running 4 tests
# test test_audit_trail::test_verify_integrity_tampering ... ok
# test test_audit_trail::test_public_queries ... ok
# test test_audit_trail::test_append_and_get_record ... ok
# test test_audit_trail::test_verify_integrity ... ok
# test result: ok. 4 passed; 0 failed; 0 ignored; 0 measured; 270 filtered out; finished in 0.06s

# Run full suite
cargo test
# Expected output: test result: ok. 274 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 1.73s

Manual Testing Steps

1. Deploy contract in a mock environment.
2. Call initialize and verify record 1 is created.
3. Call create_market and verify record 2 links to record 1.
4. Manually mutate a record in storage during a test and verify verify_audit_integrity returns false.

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📚 Documentation

Documentation Updates

• README updated
• Code comments added/updated
• API documentation updated
• Examples updated
• Deployment instructions updated
• Contributing guidelines updated
• Architecture documentation updated (walkthrough.md)

Breaking Changes

Breaking Changes:

• None. All new methods are additive, and existing method signatures remain unchanged (internals were updated to include audit logging).

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🔍 Code Quality

Code Review Checklist

• Code follows Rust/Soroban best practices
• Self-review completed
• No unnecessary code duplication
• Error handling is appropriate
• Logging/monitoring added where needed
• Security considerations addressed
• Performance implications considered
• Code is readable and well-commented
• Variable names are descriptive
• Functions are focused and small

Performance Impact

• Gas Usage: Minimal increase for sensitive actions due to persistent storage writes and SHA-256 hashing.
• Storage Impact: Each sensitive action adds one AuditRecord to persistent storage.
• Computational Complexity: O(D) for verify_integrity where D is the verification depth. Append is O(1).

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🚀 Deployment & Integration

Deployment Notes

• Network: Testnet/Mainnet
• Migration Required: No

Integration Points

• Frontend integration considered (Query functions exposed)
• API changes documented
• Backward compatibility maintained

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📊 Impact Assessment

User Impact

• End Users: Enhanced trust in market integrity and administrative transparency.
• Developers: Easy access to historical audit data via on-chain queries.
• Admins: All actions are now publicly auditable and non-repudiable.

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✅ Final Checklist

Pre-Submission

• Code follows Rust/Soroban best practices
• All CI checks passing
• No breaking changes (or breaking changes are documented)
• Ready for review
• PR description is complete and accurate
• All required sections filled out
• Test results included
• Documentation updated

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