add test for resolving dispute refund when buyer is not set

[Elizabeth-dev270]

closes #151

PR: Fix [BUG-006] resolve_dispute RefundToBuyer panic (regression test)

Summary

• Issue: [BUG-006] resolve_dispute(RefundToBuyer) may unwrap a None buyer and trap the contract (panic), leaving escrows permanently Disputed.
• This change adds a regression test that reproduces the unsafe path and asserts the contract returns EscrowHasNoBuyer instead of trapping.

What changed

• Added test: contracts/escrow/src/test_resolve_dispute_no_buyer.rs
  • Constructs an EscrowData with buyer: None and state: Disputed and an active DisputeData entry.
  • Calls resolve_dispute(..., ResolutionType::Refund) as the admin and asserts EscrowHasNoBuyer is returned (no trap).

Why

• The repository previously allowed a panic when resolving a dispute that refunded the buyer while escrow.buyer was None (open-buyer escrows or accidental None). That panics the WASM host and permanently freezes funds. The test prevents regressions and confirms code paths handling None behave as expected (return a typed error rather than trap).

Files touched

• Added: contracts/escrow/src/test_resolve_dispute_no_buyer.rs

Testing

• Run the contract test suite (escrow crate):

cd contracts/escrow
cargo test

• Or run the single test:

cd contracts/escrow
cargo test test_resolve_dispute_refund_no_buyer_returns_error

Recommended follow-ups (suggested fixes)

• Option A (safer): Make buyer: Address non-optional in EscrowData and require a buyer at create_escrow time. This eliminates the None path but is a breaking storage/API change and requires migration.
• Option B (narrower): Keep buyer: Option<Address> but harden all flows that assume a buyer exists:
  • Return EscrowHasNoBuyer (or another clear error) anywhere a buyer is required (already done in several places). Ensure no .unwrap() or unchecked clones remain for buyer.
  • Add unit/integration tests covering open-buyer and funded escrows.

Notes

• This PR only adds a regression test; it does not modify runtime behavior. The test documents the bug and prevents regressions while a code fix is applied.

Next steps

• If you want, I can implement Option B (guard resolve_dispute/payout paths to return a clear error without panicking) and add corresponding tests, then open a PR with the code fix and this test included.

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