fix(ai-gateway): strip upstream cost for custom-priced models

[chrarnoldus]

Summary

• isFreeModelRequiringCostRemoval in rewriteModelResponse is now also true for models with custom pricing (getCustomPricing(model) !== undefined), in addition to Kilo-exclusive free models. The gateway condition (openrouter/vercel) still applies. The upstream-reported cost does not reflect Kilo's custom pricing, so it must be removed from the response just like for free models.
• All optional/defaulted parameters in rewriteModelResponse.ts (removeCost = true, capture?, vercelRequestId? on the three exported rewrite functions, capture? on readResponseText/rewriteSseStream) are now required so call sites are explicit.

Test plan

• Added a regression test asserting cost fields are stripped for a custom-priced model (qwen/qwen3.7-plus); existing free-model/paid-model coverage unchanged.
• Test call sites updated for the now-required parameters.
• Relying on CI for the web test suite.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Executive Summary

No new commits since the last review; the incremental diff since the previously reviewed commit remains a pure rename (isFreeModelRequiringCostRemoval -> requiresCostRemoval) plus formatting-only changes in rewriteModelResponse.ts, with no logic change; no issues found.

Files Reviewed (2 files)

• apps/web/src/lib/rewriteModelResponse.ts - rename and formatting only, no logic change
• apps/web/src/lib/rewriteModelResponse.test.ts - unchanged since last review

Previous Review Summary (commit 13b364f)

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

Previous review (commit 13b364f)

Status: No Issues Found | Recommendation: Merge

Executive Summary

Incremental diff since the last review is a pure rename (isFreeModelRequiringCostRemoval -> requiresCostRemoval) and a comment removal in rewriteModelResponse.ts, with no logic change; no issues found.

Files Reviewed (2 files)

• apps/web/src/lib/rewriteModelResponse.ts - changed in this increment (rename only)
• apps/web/src/lib/rewriteModelResponse.test.ts - unchanged since last review

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_{Reviewed by claude-sonnet-5 · Input: 18 · Output: 5.7K · Cached: 384.1K}

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