feat(ai-gateway): add weighted routing for Auto Free models

[chrarnoldus]

Summary

• store hardcoded weights alongside Auto Free model IDs
• route sticky Auto Free selections through weighted buckets after availability filtering
• preserve the current distribution with weight 1 defaults while allowing one-value routing bias changes

Verification

• pnpm --filter web exec jest --runInBand src/lib/ai-gateway/models.test.ts src/lib/ai-gateway/auto-model/resolution.test.ts src/lib/ai-gateway/auto-routing-models.test.ts
• pnpm --filter web typecheck
• pnpm --filter web lint
• changed-file oxfmt --list-different
• git diff --check

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Executive Summary

Incremental review of commit a215c269f: the weighted-selection test assertion in models.test.ts now uses the total routing weight (4) as modulus, resolving the previous review's only finding; no new issues introduced.

Files Reviewed (1 file)

• apps/web/src/lib/ai-gateway/models.test.ts - verified: assertion modulus now matches the seed search (getRandomNumber(seed, 4)) and the bucket space consumed by selectAutoFreeModel (weights 3 + 1)

Previous Review Summary (commit 2e00a6e)

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

Previous review (commit 2e00a6e)

Status: 1 Issue Found | Recommendation: Address before merge

Executive Summary

The weighted Auto Free routing logic is correct (bucket math, availability filtering, null fallback all sound), with a single low-risk test-quality nit: a misleading modulus in the new weighted-selection test assertion in models.test.ts.

Overview

Severity	Count
CRITICAL	0
WARNING	0
SUGGESTION	1

Issue Details (click to expand)

SUGGESTION

File	Line	Issue
apps/web/src/lib/ai-gateway/models.test.ts	174	Assertion uses candidates.length (2) as modulus instead of the total weight (4) that selectAutoFreeModel actually hashes against

Files Reviewed (3 files)

• apps/web/src/lib/ai-gateway/auto-model/resolution.ts - verified: deterministic filter+sort, safe null fallback, unchanged seed semantics
• apps/web/src/lib/ai-gateway/models.ts - verified: correct weighted-bucket selection, zero-weight guard, no broken consumers
• apps/web/src/lib/ai-gateway/models.test.ts - 1 issue

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_{Reviewed by kimi-k3 · Input: 25.7K · Output: 3K · Cached: 170.9K}

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