f6a2ba6261
xAI returns HTTP 403 (not 401) with unauthenticated:bad-credentials when an OAuth2 access token has expired or is invalid. The existing _is_auth_error() only checked for 401 status codes, so these tokens were never refreshed and the 403 propagated as a generic permission denied error. Three fixes: 1. _is_auth_error: Recognize xAI's 403+bad-credentials pattern as an auth failure, triggering token refresh instead of silent failure. 2. _refresh_provider_credentials: Add xai-oauth branch with pool-level refresh (try_refresh_current with select to ensure current entry) then fallback to singleton resolver with force_refresh=True. 3. _recoverable_pool_provider: Map api.x.ai host to xai-oauth pool for auto-resolved providers, matching existing pattern for openai-codex/openrouter/nous/anthropic. Includes 14 tests covering the new detection logic, host mapping, and graceful fallback behavior. Signed-off-by: moikapy <moikapy@devmoi.com>