- A user's own key goes only to https://api.anthropic.com, https://api.openai.com/v1 or an origin listed in STC_AI_ALLOWED_BASE_URLS / the server config's allowedBaseUrls; anything else is a 400, and a stored key whose origin was later removed stops being used. - User-scope provider calls never follow redirects, and their errors reach the user only as the HTTP status plus a fixed message; the full text is logged. - The admin's server-scope provider may still use any base URL. - Admin UI: allowed origins field; MCP stdio env editable, HTTP headers kept. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>