[Backend] Complete Party Invitation and Acceptance Flow

[KuchiMercy]

Problem

This issue was previously opened as #58 but was never implemented. When an escrow is created, parties (buyer, seller, arbitrator) are added but there is no formal invitation flow. Parties cannot accept or reject invitations, and the escrow can proceed even if a party hasn't agreed to participate.

Current State

• Party entity has status field (PENDING, ACCEPTED, REJECTED) but it's never updated
• No endpoint for a party to accept or reject an invitation
• No notification sent to invited parties
• Escrow can be funded even if parties haven't accepted

Acceptance Criteria

• Add endpoint: POST /escrows/:id/parties/:partyId/accept
  • Set party status to ACCEPTED
  • Record acceptance timestamp
  • Notify escrow creator
• Add endpoint: POST /escrows/:id/parties/:partyId/reject
  • Set party status to REJECTED
  • Notify escrow creator
  • If a required party rejects, optionally cancel the escrow
• Add endpoint: GET /escrows/pending-invitations
  • List all escrows where the user has a PENDING party invitation
  • Include escrow details (title, amount, creator, other parties)
• Validate party acceptance before escrow funding:
  • All required parties (buyer + seller minimum) must have ACCEPTED status before funding is allowed
  • Return clear error if attempting to fund with unaccepted parties
• Add PARTY_INVITED notification event (ties into notification wiring issue)
• Add unit tests for accept/reject/validate flows
• Add E2E test for the complete invitation flow

Technical Notes

• Party status transitions: PENDING → ACCEPTED | REJECTED
• Only the user matching party.userId can accept/reject their own invitation
• Consider adding an expiry for invitations (auto-reject after X days)

Points: 100 (Trivial)

[zhero-o]

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

HI, I would like to work on this issue. Can I get assigned?

ℹ️ Repo Maintainers: To accept this application, review their application or assign @zhero-o to this issue.

[drips-wave]

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

🧑‍💻 @zhero-o: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

Warning

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[drips-wave]

This issue has been marked as completed by a Drips Wave moderator for @zhero-o as part of the Stellar Wave Program's 5th Wave 🥳

Moderator's reason: [Auto-assessed] The contributor successfully implemented the complete party invitation and acceptance flow as requested in issue #274. PR #384 includes the required endpoints, entity updates, migration, notification logic, and comprehensive unit tests, and it has been merged into the main codebase.

😎 @zhero-o: You earned 200 Points for completing this issue! After the current Wave ends, you'll be eligible for a percentage of the Wave's reward pool based on the percentage of total points you've earned. Learn more here.

🧑‍💻 Repo maintainers: How'd the contributor do? Leave a review to share your experience working with them.

ℹ️ Note: This issue was marked complete via moderation. Points were issued even though the GitHub issue remains open.