Show ChatGPT credit balance alongside Codex usage limits #17704

Proposal

Show the ChatGPT credit balance in Usage → Limits for Codex accounts when Codex reports it.

The weekly allowance can show 0% left while the same account still has spendable credits. Today T3 shows the allowance but drops the credit balance from the Codex response, so I have to check another app to see what is left.

Suggested behavior

Add a small “ChatGPT credits” card below the Codex allowance cards, with the remaining balance and a note that it is separate from plan allowance and reset credits. Use the existing Usage page styles in web/desktop and mobile. Keep separate account balances separate, and show unknown or unlimited states honestly.

This would only display the balance already reported by account/rateLimits/read and its update notifications. It would not change billing, model routing, spending, or reset behavior.

Evidence

Confirmed on upstream 8b81a8880: the Codex response contains credits.hasCredits, credits.unlimited and a decimal credits.balance, while T3’s usage mapper currently retains quota windows and earned reset credits only. A synthetic example is a 100%-used weekly window alongside credits.balance: "12345.6789".

OpenAI’s credits documentation describes using credits after plan limits. No account credentials or personal billing data are needed for the display.

Implementation

PR: #17705

The PR includes before/after screenshots, dark and narrow layouts, and focused regression coverage.