Guard NextContractId allocation against overflow and reuse

[mikewheeleer]

Description

create_contract reads DataKey::NextContractId, defaults to 1, and writes id + 1 using unchecked u32 addition. Near u32::MAX this wraps and could collide with an existing DataKey::Contract(id), silently overwriting an active escrow. Add overflow-safe id allocation.

Requirements and context

• Scoped to TalentTrust escrow Soroban contract (contracts/escrow).
• Use checked addition for id + 1 and panic with a dedicated overflow error if the id space is exhausted.
• Optionally assert DataKey::Contract(id) is unset before writing to detect any collision defensively.
• Invariant: contract ids are strictly monotonic and never reused; allocation fails closed at the boundary.
• Must be secure, tested, and documented.

Suggested execution

• Fork the repo and create a branch:
  • git checkout -b security/contract-id-overflow
• Implement changes:
  • contracts/escrow/src/lib.rs
  • Tests: contracts/escrow/src/test/storage.rs
  • Docs: docs/escrow/state-persistence.md
  • Include rustdoc/NatSpec-style doc comments on public functions
  • Validate security assumptions (auth, overflow, fail-closed state machine, storage TTL, fee accounting)

Test and commit

• Run tests: cargo test
• Cover edge cases (unauthorized callers, double release/refund, expired approvals, fee rounding, paused state)
• Include test output and security notes in the PR

Example commit message

fix(escrow): overflow-safe NextContractId allocation

Guidelines

• Minimum 95% test coverage on new/changed code
• Clear documentation
• Timeframe: 96 hours from assignment

[Vvictor-commits]

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

please assign this issue to me

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[drips-wave]

Congratulations, @Vvictor-commits! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

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