fix(ai-gateway): limit firewall forwarding headers

[pandemicsyn]

Summary

• pass only the host and Vercel client IP headers to the gateway inference firewall check
• preserve the existing account-scoped rate-limit key
• fail explicitly when the host required by the firewall SDK is unavailable
• add regression coverage proving unrelated request headers are not forwarded

Context

Vercel support identified that @vercel/firewall duplicates every original request header onto its internal rate-limit request. Requests with many headers can prevent the internal rate-limit identifier from being recognized, causing the SDK to report error: "not-found" even though the gateway-inference rule is configured. This change applies their allowlist workaround only to the affected gateway check.

Sentry: https://kilo-code.sentry.io/issues/7742540582/

Verification

• pnpm --filter web test -- --runTestsByPath src/lib/ai-gateway/gateway-account-rate-limit.test.ts --runInBand
• pnpm --filter web typecheck
• pnpm --filter web lint
• pnpm exec oxfmt --list-different apps/web/src/lib/ai-gateway/gateway-account-rate-limit.ts apps/web/src/lib/ai-gateway/gateway-account-rate-limit.test.ts
• git diff --check

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Executive Summary

Reviewed the incremental fallback that derives the firewall host from the request URL when the host header is absent, plus its regression test; the ?? new URL(request.url).host fallback is safe in a Next.js request context and the prior header-allowlist behavior is unchanged.

Files Reviewed (2 files)

• apps/web/src/lib/ai-gateway/gateway-account-rate-limit.ts
• apps/web/src/lib/ai-gateway/gateway-account-rate-limit.test.ts

Previous Review Summary (commit 712c8e8)

Current summary above is authoritative. Previous snapshots are kept for context only.

Previous review (commit 712c8e8)

Status: No Issues Found | Recommendation: Merge

Executive Summary

Reviewed the header-allowlist change in the AI gateway firewall check and its regression tests; the allowlist, missing-host failure, and account-scoped key look correct and consistent with existing @vercel/firewall usage in the repo.

Files Reviewed (2 files)

• apps/web/src/lib/ai-gateway/gateway-account-rate-limit.ts
• apps/web/src/lib/ai-gateway/gateway-account-rate-limit.test.ts

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_{Reviewed by deepseek-v4.1-flash · Input: 0 · Output: 0 · Cached: 0}

_{Review guidance: REVIEW.md from base branch main}