fix: align codex oauth models and request contract

[tuanminhhole]

9Router Codex OAuth Fix Draft

Closes #718

Proposed PR Title

Fix Codex OAuth request contract and narrow exposed ChatGPT-account models

Summary

• use a valid Codex /responses probe payload during provider self-test
• remove unsupported max_output_tokens before dispatching Codex requests
• narrow the exposed cx/* model list to models verified to work with ChatGPT Plus OAuth on 2026-04-21

Repro

1. Connect an OpenAI Codex OAuth account in 9Router with ChatGPT Plus.
2. Call /api/providers/:id/test or route a cx/* model through /v1/responses.
3. Observe false unavailable state or repeated 400 errors for models the account can actually use.

Root Cause

• the Codex provider self-test used an invalid payload shape:
  • empty input
  • stream: false
  • no instructions
• the executor still forwarded max_output_tokens, which the current Codex backend rejects
• the UI exposed several cx/* models that ChatGPT-account OAuth currently rejects upstream

Verified Working Models

• cx/gpt-5.4
• cx/gpt-5.4-mini
• cx/gpt-5.3-codex
• cx/gpt-5.2

Verified Rejected Models

• cx/gpt-5.3-codex-xhigh
• cx/gpt-5.3-codex-high
• cx/gpt-5.3-codex-low
• cx/gpt-5.3-codex-none
• cx/gpt-5.3-codex-spark
• cx/gpt-5.2-codex
• cx/gpt-5.1-codex-max
• cx/gpt-5.1-codex
• cx/gpt-5.1-codex-mini
• cx/gpt-5.1-codex-mini-high
• cx/gpt-5.1
• cx/gpt-5-codex
• cx/gpt-5-codex-mini

Files Changed In Upstream Draft

• .tmp/9router-upstream/open-sse/executors/codex.js
• .tmp/9router-upstream/open-sse/config/providerModels.js
• .tmp/9router-upstream/src/app/api/providers/[id]/test/testUtils.js
• .tmp/9router-upstream/README.md

Suggested PR Body

This patch fixes a Codex OAuth mismatch against the current ChatGPT-backed Codex /responses backend.

Changes:

• send a valid payload during Codex provider self-test so accounts are not marked unavailable because of schema errors
• strip max_output_tokens before forwarding Codex requests
• narrow the exposed cx/* list to models that were verified working with ChatGPT Plus OAuth on 2026-04-21

Why:

• the previous self-test payload could fail even when the token was valid
• current backend contract requires instructions, list-form input, stream: true, and store: false
• several exposed Codex models are currently rejected upstream for ChatGPT-account OAuth and should not be offered as ready-to-use defaults