Follow-up to #26534 (xai-oauth provider). The new guide and integrations
page were shipped with the salvage, but four reference/enumeration pages
still listed every other OAuth provider without xai-oauth:
- reference/cli-commands.md — `--provider` choices list
- reference/environment-variables.md — HERMES_INFERENCE_PROVIDER values
- user-guide/configuration.md — auxiliary-task provider list, OAuth
tip block (mirrored from MiniMax OAuth),
and provider table row
- user-guide/features/fallback-providers.md — provider table