fix(auth): resolve GitHub OAuth error=github redirect loop

[Mayur-e]

What this fixes

Closes #1221

After clicking "Sign in with GitHub", users were redirected back to /auth/signin?error=github instead of the dashboard.

Root causes found & fixed

1. src/lib/auth.ts

• Added supabaseAdmin null guard in signIn callback — when Supabase env vars are missing, calling .from() on null threw a TypeError that NextAuth silently converted to error=github
• Wrapped DB operations in try/catch so transient errors never block login

2. src/app/auth/signin/page.tsx

• Added AuthErrorBanner that shows a human-readable error message when ?error= is in the URL
• Clears the error param from the URL after display to prevent stale errors on refresh
• Wrapped useSearchParams() in <Suspense> for Next.js 14 compatibility

3. src/components/landing/LandingPage.tsx

• Sign-in links used raw href="/api/auth/signin/github" bypassing NextAuth CSRF — changed to href="/auth/signin"

4. DEVELOPMENT.md

• Added error=github troubleshooting checklist

Testing

• ✅ npm run lint — no warnings or errors
• ✅ npm run build — all 11 pages compiled
• ✅ Tested locally: home → sign-in → GitHub OAuth → dashboard ✅

Screenshots

Before — URL shows error=github but no feedback given to user

After — Clean sign-in page on fresh visit

After — Successful login reaches dashboard

Video.webm

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[Priyanshu-byte-coder]

Thanks @Mayur-e for the comprehensive work here! We just merged #1334 which also touches src/lib/auth.ts (useSecureCookies fix + cookie config).

The unique parts of your PR that we want to keep:

• DEVELOPMENT.md troubleshooting guide (the OAuth error=github walkthrough)
• src/components/landing/LandingPage.tsx sign-in link changes (good fix!)
• src/app/auth/signin/page.tsx — Suspense wrapper + AuthErrorBanner
• src/lib/auth.ts — the supabaseAdmin null guard (unique and important!)

Please rebase onto main (which now has #1334 merged) and resolve any conflicts in auth.ts. The null guard (if (!supabaseAdmin) { ... return true; }) should be kept as it prevents crashes when Supabase env vars are missing. Looking forward to the updated version!

[Mayur-e]

Rebased onto main (which includes #1334) and resolved the auth.ts conflict.

What was kept from #1334:

• cookies block (secure cookie config with useSecureCookies)
• Email field in the Supabase upsert
• 42703 error fallback (graceful handling of missing email column)

What was kept from this PR:

• supabaseAdmin null guard — placed before the try block so .from() is never called on null
• AuthErrorBanner on sign-in page
• Landing page sign-in link fix
• DEVELOPMENT.md troubleshooting guide

Also fixed a pre-existing lint error in src/lib/supabase.ts introduced by #1334 — the eslint-disable-next-line @typescript-eslint/no-explicit-any comment referenced a rule not configured in this project's ESLint setup, causing next lint to fail.

✅ npm run lint — no warnings or errors

[Mayur-e]

Also noticed and fixed a pre-existing YAML syntax error in .github/workflows/e2e.yml
at line 37 — the Install Playwright browsers step had 12 spaces of indentation
instead of 6, making GitHub Actions fail to parse the workflow file entirely.

Fixed: - name: → - name: (standard step indentation)

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