fix: preserve Fable fallback on Vercel

[chrarnoldus]

Summary

• avoid forcing Fable requests through Amazon Bedrock on Vercel
• preserve the configured Claude Opus fallback
• add regression coverage for Fable provider ordering

Testing

• pnpm --filter web test -- --runInBand apps/web/src/lib/ai-gateway/providers/apply-provider-specific-logic.test.ts
• pnpm --filter web lint
• pnpm --filter web typecheck
• git diff --check

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Executive Summary

Reviewed the Fable/Vercel provider-order fix and its regression test; the guard correctly excludes Fable from the Bedrock/Anthropic preferred-provider order without affecting the existing Opus fallback logic, and no high-confidence bugs were found in the changed lines.

Files Reviewed (2 files)

• apps/web/src/lib/ai-gateway/providers/apply-provider-specific-logic.ts
• apps/web/src/lib/ai-gateway/providers/apply-provider-specific-logic.test.ts

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_{Reviewed by claude-sonnet-5 · Input: 28 · Output: 5.5K · Cached: 540.1K}

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