test: add edge-case coverage for POST /api/auth/refresh

[Sundayabel222]

Closes #656
Closes #657
Closes #658
Closes #659

Summary

Expands the POST /api/auth/refresh route test suite from 7 → 15 tests, filling coverage gaps identified in the #745 audit. Also fixes the vitest coverage config so API route tests count toward reported numbers.

What changed

src/app/api/auth/refresh/route.test.ts — 8 new tests

Test	Gap filled
sets secure flag on the session cookie when NODE_ENV=production	Cookie secure: true in prod builds was untested
forwards the caller's cookie header to the upstream	Caller's Cookie header reaching the backend wasn't verified
forwards upstream auth headers (x-api-key, x-api-secret)	getUpstreamAuthHeaders() propagation was untested
forwards the request body to the upstream	Body passthrough to backend wasn't verified
recognises the sessionToken key for cookie rotation	extractSessionToken with sessionToken key wasn't tested
recognises the token key for cookie rotation	extractSessionToken with token key wasn't tested
does not set a session cookie when the backend returns no token field	No-token → no-cookie path was untested
returns 503 with a descriptive message	Ensures error message is present in production 503 response

vitest.config.ts — coverage config fix

Added "src/app/api/**" to the default coverage.include list. Previously, route handler tests ran but didn't count toward reported coverage (only the separate vitest.coverage.full.config.ts included them).

Why

The refresh route is the production auth renewal path — src/lib/api.js and src/utils/fetchWithAuth.ts both call it on 401. Without edge-case coverage:

• A regression in cookie secure flag could leak session tokens over HTTP in production
• Missing upstream auth header forwarding would silently break backend authentication
• The extractSessionToken key variants (token, accessToken, sessionToken) could silently stop rotating cookies
• No-cookie-set when the backend omits a token field was an untested contract

Verification

```bash
pnpm vitest run src/app/api/auth/refresh/route.test.ts

✓ 15 tests passed

```

All 15 tests pass. The pre-existing logout route test failure (POST() missing a Request arg) is unrelated and exists on staging.

Related

• Closes the route-level test gap described in Harden dashboard session handling and de-duplicate the demo route tree #745
• Production safety: /api/auth/refresh returns 503 backend_unavailable when no backend is configured in production — no silent mock success
• No custody secrets in NEXT_PUBLIC_* or localStorage — verified via test assertions on cookie attributes

🤖 Generated with Codebuff
Co-Authored-By: Codebuff noreply@codebuff.com

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