Stoff81/chatgpt5.5

[Stoff81]

Summary

Adds ChatGPT subscription support for GPT-5.5 through the Responses API path.

This includes:

• registering chatgpt/gpt-5.5 as a supported ChatGPT model
• routing ChatGPT Responses API requests to the native Codex backend
• normalizing ChatGPT Responses payloads for Codex compatibility
• supporting streaming Responses API output from ChatGPT
• wiring ChatGPT subscription auth/token handling through the CLI

Why

The ChatGPT Codex subscription backend is close to OpenAI’s Responses API, but not identical. It rejects or expects different forms for several fields, so plain OpenAI-compatible forwarding is not enough.

This PR adapts those differences so Plano can use a ChatGPT subscription as a local upstream provider for GPT-5.5.

Notable behavior

For ChatGPT Responses requests, Plano now:

• requires streaming requests
• sets store=false
• wraps string input as list input
• omits unsupported fields such as truncation
• handles ChatGPT-specific token field behavior
• flattens typed text content parts where required
• preserves/normalizes reasoning and function-call items for the Codex backend
• buffers/translates streaming events into OpenAI Responses-compatible output

Testing

• Added/updated ChatGPT provider/request adapter tests
• Verified ChatGPT Responses streaming locally with chatgpt/gpt-5.5
• Verified existing provider routing behavior still passes