@tanstack/ai-openrouter: optional structured output fields are rewritten as nullable but rejected by original schema validation

[DrewHoo]

TanStack AI version

0.24.0

Framework/Library version

@tanstack/ai-openrouter 0.11.0

Describe the bug and the steps to reproduce it

1. User provides a Standard Schema where a field is optional.
2. TanStack converts it to JSON Schema.
3. OpenRouter adapter rewrites optional fields into required + nullable for strict OpenAI/OpenRouter compatibility.
4. Model returns null for that field, which the provider schema allowed.
5. TanStack validates the result against the original Standard Schema, which rejects null.

Your Minimal, Reproducible Example - (Sandbox Highly Recommended)

https://stackblitz.com/edit/dkxh99pz?file=package.json

Screenshots or Videos (Optional)

Do you intend to try to help solve this bug with your own PR?

Maybe, I'll investigate and start debugging

Terms & Code of Conduct

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• I understand that if my bug cannot be reliable reproduced in a debuggable environment, it will probably not be fixed and this issue may even be closed.