feat: implement the reject and refund features

[dinahmaccodes]

SkillSphere Pull Request

• Closes Implement "Reject & Refund" (Expert Action) #16
• Added tests
• Ran cargo test (All tests passed)
• Evidence attached (Screenshots, Logs, or Transaction Hashes)
• Commented the code

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Tests added passed. General tests passed as well

Added 6 comprehensive test cases covering:
Successful rejection with refund
Authorization enforcement (user/wrong expert)
Status validation (Complete/Reclaimed sessions)
Error handling (non-existent bookings)

Images:

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📌 Type of Change

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ✨ Enhancement (non-breaking change which adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to change)
• 🏗️ Refactor (code improvement/cleanup without logical changes)

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📝 Changes Description

Better description of tasks

Added reject_session functionality allowing experts to instantly decline pending consultation bookings with automatic full refunds to users.

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📸 Evidence

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Closes #16

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Summary by CodeRabbit

• New Features

  • Experts can now reject pending bookings, automatically refunding the user.
  • Added "Rejected" status to the booking lifecycle.

• Tests

  • Added comprehensive test coverage for rejection scenarios, including authorization validation and edge cases.

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[coderabbitai]

📝 Walkthrough

Walkthrough

This PR implements an expert-initiated session rejection feature, allowing experts to decline pending bookings and refund the user's deposit instantly. It adds the reject_session logic, corresponding event emission, type definitions, comprehensive tests, and updates the BookingStatus enum with a new Rejected variant.

Changes

Cohort / File(s)	Summary
Core Rejection Logic contracts/payment-vault-contract/src/contract.rs, contracts/payment-vault-contract/src/events.rs, contracts/payment-vault-contract/src/lib.rs	Introduces reject_session function with expert authorization, pending status validation, deposit transfer back to user, status update to Rejected, and corresponding session_rejected event emission. Public API method delegates to core contract logic.
Type Definitions contracts/payment-vault-contract/src/types.rs	Updates BookingStatus enum to add Rejected = 2 variant and shifts Reclaimed discriminant from 2 to 3.
Test Suite contracts/payment-vault-contract/src/test.rs	Adds six comprehensive unit tests covering expert rejection of pending sessions, authorization validation, state transition edge cases (Complete and Reclaimed bookings), wrong expert rejection attempts, and non-existent booking handling.

Sequence Diagram

sequenceDiagram
    participant Expert
    participant Contract as Payment Vault<br/>Contract
    participant Storage as Booking<br/>Storage
    participant User

    Expert->>Contract: reject_session(booking_id)
    Contract->>Contract: expert.require_auth()
    Contract->>Storage: Load booking
    Storage-->>Contract: booking data
    Contract->>Contract: Verify caller == booking.expert
    Contract->>Contract: Check booking.status == Pending
    Contract->>User: Transfer total_deposit
    User-->>Contract: Refund received
    Contract->>Storage: Update status to Rejected
    Storage-->>Contract: Status updated
    Contract->>Contract: Emit session_rejected event

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Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• PR #14: Modifies BookingStatus and BookingRecord type definitions in the same types.rs file; the main PR adds the Rejected variant while interacting with existing Reclaimed and Complete statuses introduced in that PR.
• PR #11: Both PRs modify the booking lifecycle across contract.rs, events.rs, lib.rs, and test.rs; this PR extends the lifecycle with rejection semantics alongside existing finalization and reclamation flows.

Poem

A clever fox rejects with grace,
Refunds returned to rightful place,
Pending sessions meet their end,
Hopping onward, funds to send! 🐰✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main feature addition of implementing reject and refund functionality for experts.
Linked Issues check	✅ Passed	Code changes fully implement issue #16 requirements: BookingStatus enum updated with Rejected/Reclaimed variants [#16], session_rejected event function added [#16], reject_session implemented with expert auth and pending status check [#16], fund transfer and status update logic present [#16], comprehensive test coverage added [#16].
Out of Scope Changes check	✅ Passed	All changes are directly scoped to issue #16 requirements. No unrelated modifications detected in contract logic, event handling, types, or test additions.
Docstring Coverage	✅ Passed	Docstring coverage is 92.86% which is sufficient. The required threshold is 80.00%.
Description check	✅ Passed	PR description includes issue reference, test attestation, evidence (screenshots), and code changes overview, but lacks detail on breaking changes impact and specific comments about edge cases.

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✨ Finishing touches

• 📝 Generate docstrings

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[dinahmaccodes]

@Bosun-Josh121 Please review PR