Feature/transaction contract improvements

[KevinMB0220]

🚀 Transaction Management Smart Contract – NFTopia (Stellar)

📌 Summary

This PR delivers a complete implementation of the Transaction Management Smart Contract for NFTopia on Stellar.
It provides a robust state machine, atomic execution with rollback, multi-signature support, advanced NFT operations, and a fully passing test suite.

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✅ Status

• Tests: 7/7 passing successfully
• Contract: Production-ready and ready for NFTopia integration
• Snapshots: Removed from the repository and properly ignored via .gitignore

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📦 Files Changed

• Cargo.toml – Updated configuration using Soroban SDK v23 and testutils
• lib.rs – Full contract implementation (~1,100 lines)
• README.md – Comprehensive documentation
• .gitignore – Added test_snapshots/
• ❌ Removed: previously committed test snapshot files

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🔄 Transaction State Machine

• Draft → Pending → Executing → Completed / Failed / Cancelled / RolledBack

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🧩 Supported NFT Operations (12)

• Mint, Transfer, Burn
• ListForSale, CancelListing, Purchase
• PlaceBid, AcceptBid
• Bundle, Unbundle
• UpdateMetadata, SetRoyalty

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🛠 Core Features

• create_transaction – Create atomic transactions
• add_operation – Add operations with dependencies
• submit_transaction – Submit for execution
• sign_transaction – Multi-signature support
• execute_transaction – Atomic execution with rollback
• cancel_transaction – Cancel pending transactions
• estimate_gas – Gas estimation with budget enforcement

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⚡ Batch & Advanced Capabilities

• Batch create, execute, and verify transactions
• Parallel execution optimizations
• Automatic dependency resolution (topological sort)
• Circular dependency detection
• Checkpoint-based recovery
• Event emission (7 event types) for external integrations

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🔐 Security Considerations

• Authorization enforced on all operations
• Multi-signature support for high-value actions
• Gas limits to prevent runaway execution
• Strict dependency validation
• Atomic execution guarantees
• Unique transaction IDs

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🧪 Test Coverage

• Transaction creation
• Operation management
• Full transaction lifecycle
• Gas estimation
• Batch operations
• Multi-signature flows
• Dependency resolution

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🧹 Repo Hygiene

• Removed all previously committed test snapshot files
• Added test_snapshots/ to .gitignore to prevent future commits

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Close #344

🎯 Result

This contract provides a solid, secure, and extensible foundation for managing complex multi-step NFT operations in the NFTopia Stellar ecosystem.

[KevinMB0220]

@Oluwaseyi89 can you review my pr please the wave almost end