Add GPT-6.1 Terra support #2380

Is your feature request related to a problem? Please describe.

Zoo Code does not list GPT-6.1 Terra for the native OpenAI provider or the ChatGPT subscription Codex provider. Users cannot select the model with its official context, reasoning, caching, and pricing metadata.

Describe the solution you'd like

Add GPT-6.1 Terra to both OpenAI model catalogs without changing the current default models.

Use the official native API metadata. This includes the 1,050,000-token context window, the 128,000-token output limit, image input, prompt caching, supported reasoning efforts, and service-tier pricing.

Use the official Codex metadata for subscription requests. This includes the supported 872,000-token maximum context window, low default reasoning, and Responses Lite routing.

Add focused tests for model metadata, reasoning selection, native tool requests, service-tier pricing, and Codex tool request shaping.

Describe alternatives you considered

Users can enter a custom model ID through a compatible provider. This does not provide the verified metadata or the native Codex subscription flow. It can also apply incorrect limits and pricing.

Additional context

Official sources:

• https://developers.openai.com/api/docs/models/gpt-6.1-terra
• https://developers.openai.com/api/docs/guides/latest-model
• https://developers.openai.com/api/docs/pricing
• https://github.com/openai/codex/blob/main/codex-rs/models-manager/models.json

Implementation PR: #2379