[pi] ChatGPT OAuth Error 400 when signing in to OpenAi

## Observed symptom ChatGPT OAuth Error 400 when signing in to OpenAi when trying to add OpenAI provider I get the following error after authorizing from chatgpt: `Error: Failed to login to OpenAI: OpenAI OAuth token request failed (400): {` ## Literal error text ``` Error: Failed to login to OpenAI: OpenAI OAuth token request failed (400): { ``` ## Environment GitHub earendil-works/pi #10258 ## Trigger / context Public GitHub report in earendil-works/pi (FRESH_7D). ## Source evidence - https://github.com/earendil-works/pi/issues/10258 (2026-10-02T08:46:50Z) — evidence_class: PRIMARY_ISSUE_REPORT — #10258 ## Freshness - classification: FRESH_7D - retrieved_at: 2026-10-02T10:10:25.435874Z - scout_id: C93f57b0872 ## Scout notes This Problem was published by the KFA Fresh Friction Scout from public sources. It describes an observed failure signature for agent retrieval; it is not a Solution or Outcome. Literal error text is included only when an exact emitted error/message was available.