fix: resolve race condition in reply voting system

[ash1shkumar]

Description

Implemented a transaction-safe reply voting system to prevent race conditions and vote count desynchronization during concurrent requests.

Changes Made

• wrapped reply voting operations inside db.transaction()
• converted vote updates into atomic DB operations
• prevented partial updates during concurrent voting
• added protection against negative vote counts using GREATEST()
• improved backend consistency for rapid/multi-tab voting scenarios
• added graceful duplicate vote error handling

Related Issue

Closes #329

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Documentation update (README, guides, comments)
• Style / UI change (no logic change)
• Code refactor (no behavior change)
• Test addition or update
• Breaking change (fix or feature that would cause existing functionality to change)

How Has This Been Tested?

• Tested locally with npm run dev
• Verified on mobile viewport (375px)
• Verified on desktop viewport (1440px)

Manual Testing Performed

• rapid repeated vote/unvote actions
• multi-tab concurrent voting simulation
• verified prevention of negative vote counts
• verified vote consistency during concurrent operations

Checklist

• I have tested my changes locally (npm run dev)
• My code follows the existing code style (TypeScript, Tailwind, no any types)
• I have not introduced unrelated changes (each PR should address one issue)
• I have added comments where necessary
• My branch is up to date with main
• I have linked the related issue above
• Screenshots are included (if this is a UI change)

##Expected Level
Level3/advanced

I am contributing under GSSoC and NSoC

[vercel]

@ash1shkumar is attempting to deploy a commit to the Karan Mani Tripathi 's projects Team on Vercel.

A member of the Team first needs to authorize it.

[github-actions]

Technical Review

Hi @ash1shkumar! Thank you for your contribution to DoubtDesk.

The code changes look good. Before we can complete the technical review, approve, and merge this pull request, we have one final requirement for all contributors: Please star the DoubtDesk repository.

Once you have starred the repository, please drop a comment here saying "done" (or we will automatically detect it) and we will proceed with approving and merging your PR. Thank you.

[github-actions]

Hello there! 🎉 Thank you so much for your first pull request to DoubtDesk!

We really appreciate your contribution. A maintainer will review your code soon. If you are participating in GSSoC, ensure your PR is linked to an open issue. Please make sure you have followed all rules in our Contributing Guidelines. Happy coding!

[ash1shkumar]

Technical Review

Hi @ash1shkumar! Thank you for your contribution to DoubtDesk.

The code changes look good. Before we can complete the technical review, approve, and merge this pull request, we have one final requirement for all contributors: Please star the DoubtDesk repository.

Once you have starred the repository, please drop a comment here saying "done" (or we will automatically detect it) and we will proceed with approving and merging your PR. Thank you.

done

[ash1shkumar]

Hi @knoxiboy , could you please review this PR when available?

This fix addresses a backend race condition and transactional consistency issue in the reply voting system by implementing atomic DB transactions and preventing vote count desynchronization during concurrent requests.

Since the issue involves concurrency handling, database integrity, and transaction-safe operations, I believe it would fit better under a level:advanced label instead of level:beginner.

Thank you!

[ash1shkumar]

@knoxiboy , This PR fix addresses a backend race condition and transactional consistency issue in the reply voting system by implementing atomic DB transactions and preventing vote count desynchronization during concurrent requests.

Since the issue involves concurrency handling, database integrity, and transaction-safe operations, I believe it would fit better under a level:advanced label instead of level:beginner.

Thank you!