feat(contracts): add milestone deadlines and time-locked escrow protections to escrow contract

[devkylian-tech]

Overview

Adds time-locked escrow protections to the Soroban escrow contract. Each milestone already carried a deadline field; this change completes the lifecycle around it — authorized deadline set/extend, on-chain expiry detection, client-initiated refunds after expiry, dispute lock-out, and guards that block submission/approval/release once a deadline has elapsed. New deadline events are published: DeadlineSet, DeadlineExtended, DeadlineExpired (alongside the existing RefundIssued).

Related Issue

#221 — [Feature]: Time-Locked Escrow & Milestone Deadlines

Changes

Escrow contract (contracts/contracts/escrow/src/lib.rs)

• [ADD] set_deadline(milestone_id, caller, deadline)
  • Assigns a deadline to a milestone created without one. require_auth + role check restricts it to the client or arbiter; past deadlines are rejected (InvalidDeadline) and the call emits DeadlineSet.
• [ADD] extend_deadline(milestone_id, caller, new_deadline)
  • Authorized extension (client or arbiter only) that must move strictly forward in time. Supports the Expired -> Extended transition and emits DeadlineExtended.
• [ADD] claim_expired_refund(milestone_id, caller)
  • Client-initiated refund once env.ledger().timestamp() > milestone.deadline. Refunds Funded/Submitted milestones and emits DeadlineExpired + RefundIssued. Milestones with an open dispute stay locked (MilestoneDisputed) pending arbitration.
• [MODIFY] approve and release
  • Both now return DeadlineExceeded when the milestone deadline has elapsed, so expired work can no longer be approved or paid out.
• [MODIFY] auto_expire
  • Additionally emits DeadlineExpired next to the existing MilestoneExpired event.
• [ADD] typed errors DeadlineNotExpired (13), InvalidDeadline (14), DeadlineAlreadySet (15), MilestoneDisputed (16), plus the DeadlineSet, DeadlineExtended, and DeadlineExpired events.

Tests (contracts/contracts/escrow/src/test.rs)

• [ADD] 21 unit tests covering authorized/unauthorized set & extend, invalid/past/backwards deadlines, expiry guards on submit/approve/release, client refunds after expiry (funded-with-no-submission and submitted), disputes raised after expiry with funds locked then resolved by the arbiter, multiple milestones expiring at the same timestamp, and DeadlineExpired emission.
• [ADD] generated contracts/contracts/escrow/test_snapshots/test/*.json files for the new tests.

Verification Results

Ran the repo's real Rust test command in a local checkout (REST tarball of main):

$ cd contracts && cargo test -p escrow

running 42 tests
...
test result: ok. 42 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.67s

All 42 tests pass — the 21 pre-existing tests (unchanged behaviour, since milestones with deadline == 0 skip the new guards) plus the 21 new tests. No compiler warnings were produced.

Also ran the repo's real contract build (stellar contract build, stellar-cli 27.0.0), which produced an optimized wasm exposing the new entrypoints:

$ cd contracts && stellar contract build

✅ Build Complete
    Wasm File: target/wasm32v1-none/release/escrow.wasm (19367 bytes optimized)
    Wasm Hash: 8e41c01b40fd83bb065de24784ffecefc7b7c50bc7fd449253a52201db9a7b79
    Exported Functions: 26 found
      • approve
      • auto_expire
      • claim_expired_refund
      • extend_deadline
      • set_deadline
      ...

Acceptance Criteria	Status
Contract rejects milestone approval/release after the deadline expired	✅ approve/release return DeadlineExceeded (#11); test_approve_after_deadline_expired_fails, test_release_after_deadline_expired_fails
Only client or arbitrator can modify deadlines	✅ set_deadline/extend_deadline require auth and check the caller role, else Unauthorized (#7)
Expired milestones handled gracefully (refund or locked)	✅ claim_expired_refund refunds Funded/Submitted; Disputed stays locked (#16)
Multiple milestones expiring simultaneously	✅ test_multiple_milestones_expiring_simultaneously
Disputes raised after expiry	✅ test_dispute_can_be_raised_after_expiry, test_claim_refund_locked_when_disputed_after_expiry, test_arbiter_resolves_dispute_raised_after_expiry
Escrow funded but no submission	✅ test_client_refund_after_expiry_when_funded_no_submission
Events DeadlineSet, DeadlineExpired, DeadlineExtended, RefundIssued	✅ emitted from set_deadline, auto_expire/claim_expired_refund, extend_deadline, and claim_expired_refund

Closes #221

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[devkylian-tech]

Merge conflict with main resolved

Pushed merge commit 5e40909c6c into this branch (main @ d62386535d). This is a merge commit, not a force-push, so the commit history is intact.

Conflicting file(s) resolved:

• contracts/contracts/escrow/test_snapshots/test/test_approve_after_deadline_expired_fails.1.json[hand-resolved]
• contracts/contracts/escrow/test_snapshots/test/test_arbiter_resolves_dispute_raised_after_expiry.1.json[hand-resolved]
• contracts/contracts/escrow/test_snapshots/test/test_auto_expire_emits_deadline_expired.1.json[hand-resolved]
• contracts/contracts/escrow/test_snapshots/test/test_claim_refund_locked_when_disputed_after_expiry.1.json[hand-resolved]
• contracts/contracts/escrow/test_snapshots/test/test_client_refund_after_expiry_when_funded_no_submission.1.json[hand-resolved]
• contracts/contracts/escrow/test_snapshots/test/test_client_refund_after_expiry_when_submitted.1.json[hand-resolved]
• contracts/contracts/escrow/test_snapshots/test/test_client_refund_before_expiry_fails.1.json[hand-resolved]
• contracts/contracts/escrow/test_snapshots/test/test_client_refund_unauthorized_fails.1.json[hand-resolved]
• contracts/contracts/escrow/test_snapshots/test/test_dispute_can_be_raised_after_expiry.1.json[hand-resolved]
• contracts/contracts/escrow/test_snapshots/test/test_expired_milestone_can_be_extended_then_submitted.1.json[hand-resolved]
• contracts/contracts/escrow/test_snapshots/test/test_extend_deadline_backwards_fails.1.json[hand-resolved]
• contracts/contracts/escrow/test_snapshots/test/test_extend_deadline_by_arbiter_succeeds.1.json[hand-resolved]
• contracts/contracts/escrow/test_snapshots/test/test_extend_deadline_unauthorized_fails.1.json[hand-resolved]
• contracts/contracts/escrow/test_snapshots/test/test_extend_deadline_without_existing_deadline_fails.1.json[hand-resolved]
• contracts/contracts/escrow/test_snapshots/test/test_multiple_milestones_expiring_simultaneously.1.json[hand-resolved]
• contracts/contracts/escrow/test_snapshots/test/test_release_after_deadline_expired_fails.1.json[hand-resolved]
• contracts/contracts/escrow/test_snapshots/test/test_set_deadline_in_past_fails.1.json[hand-resolved]
• contracts/contracts/escrow/test_snapshots/test/test_set_deadline_stores_value_and_emits_event.1.json[hand-resolved]
• contracts/contracts/escrow/test_snapshots/test/test_set_deadline_twice_fails.1.json[hand-resolved]
• contracts/contracts/escrow/test_snapshots/test/test_set_deadline_unauthorized_fails.1.json[hand-resolved]
• contracts/contracts/escrow/test_snapshots/test/test_submit_after_deadline_expired_fails.1.json[hand-resolved]
• contracts/contracts/escrow/src/lib.rs[hand-resolved]
• contracts/contracts/escrow/src/test.rs[hand-resolved]

The pull request is mergeable again — CI will re-run on the new head. @SudiptaPaul-31 ready for review and merge when you have a moment.