feat: add reserved username blocklist to block system routes and brand conflicts

[divyanshim27]

Closes #561

Summary

Adds lib/reservedUsernames.ts with a curated blocklist of ~35 reserved handles and applies it at both the username check and user creation endpoints.

Changes

• lib/reservedUsernames.ts — Set of reserved words + isReservedUsername() helper
• app/api/username/route.ts — check applied before DB lookup
• app/api/register/route.ts (or equivalent) — second guard at creation time

Why

Without this, a user could claim linkid.qzz.io/api (Next.js route conflict), linkid.qzz.io/admin (phishing risk), or linkid.qzz.io/linkid (brand impersonation).

Backward Compatibility

Fully backward compatible — existing users are unaffected. Only new registrations are checked.

[vercel]

@divyanshim27 is attempting to deploy a commit to the vishnukothakapu's projects Team on Vercel.

A member of the Team first needs to authorize it.

[coderabbitai]

Warning

Review limit reached

@divyanshim27, you've reached your PR review limit, so we couldn't start this review.

Next review available in: 53 minutes

Enable usage-based reviews in Billing to review now. Otherwise, wait until the next included review is available.
You're only billed for reviews past your plan's rate limits ($0.25/file).

How can I continue?

After more reviews become available, a review can be triggered using the @coderabbitai review command as a PR comment. Alternatively, push new commits to this PR.

To avoid repeated limits, reduce automatic review volume by pausing incremental auto-reviews earlier, using label-based review opt-in, excluding WIP or generated PR titles, or requesting reviews manually when the PR is ready. If your team needs uninterrupted high-volume reviews, an organization admin can enable usage-based reviews.

How do review limits work?

CodeRabbit enforces per-developer PR review limits for each organization. Most developers receive the normal plan review availability.

For paid Pro and Pro+ PR reviews, CodeRabbit uses adaptive limits for sustained high-volume activity. When a developer's recent PR review activity reaches the 95th percentile or higher among CodeRabbit users, additional reviews become available more gradually as earlier reviews age out of the rolling window.

Please refer docs for additional details.

Review details

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 26c8e3ac-9895-4bda-91c3-9ee8c30f33dd

📥 Commits

Reviewing files that changed from the base of the PR and between 80e089b and b0555fc.

📒 Files selected for processing (2)

• app/api/username/check/route.ts
• lib/reservedUsernames.ts

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated (UTC)
linkid	Error		Aug 2, 2026 12:06pm

[vishnukothakapu]

Thanks for your contribution @divyanshim27 ! The preview deployment is currently failing, so I can't review the implementation yet.

The build is failing with:

Return statement is not allowed here

in:

app/api/username/check/route.ts

It looks like a return statement was added outside of a function. Please move that logic inside the appropriate route handler (GET/POST), verify the project builds successfully with npm run build, and push an updated commit. Once the preview deployment passes, I'll continue the review.