OpenAI's OAuth token endpoint returns errors in a nested shape —
{"error": {"code": "refresh_token_reused", "message": "..."}} —
not the OAuth spec's flat {"error": "...", "error_description": "..."}.
The existing parser only handled the flat shape, so:
- `err.get("error")` returned a dict, the `isinstance(str)` guard
rejected it, and `code` stayed `"codex_refresh_failed"`.
- The dedicated `refresh_token_reused` branch (with its actionable
"re-run codex + hermes auth" message and `relogin_required=True`)
never fired.
- Users saw the generic "Codex token refresh failed with status 401"
when another Codex client (CLI, VS Code extension) had consumed
their single-use refresh token — giving no hint that re-auth was
required.
Parse both shapes, mapping OpenAI's nested `code`/`type` onto the
existing `code` variable so downstream branches (`refresh_token_reused`,
`invalid_grant`, etc.) fire correctly.
Add regression tests covering:
- nested `refresh_token_reused` → actionable message + relogin_required
- nested generic code → code + message surfaced
- flat OAuth-spec `invalid_grant` still handled (back-compat)
- unparseable body → generic fallback message, relogin_required=False
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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