Follow-up to the static list refresh: replace the hardcoded xAI entries
with _xai_curated_models(), mirroring the _codex_curated_models()
pattern from PR #7844. The helper reads $HERMES_HOME/models_dev_cache.json
at import time (no network call) and falls back to a small static list
when the cache is missing or malformed.
Why: _PROVIDER_MODELS["xai"] has drifted once already (issue #16699) and
will drift again next time xAI renames a model. Hermes already maintains
the models.dev cache and uses it for context-length lookups; pointing
_PROVIDER_MODELS at the same source means the /model picker self-heals on
the next cache refresh instead of requiring a PR.
Behavior:
- With cache populated (normal user): shows every current xAI model ID,
picks up renames automatically on next refresh.
- Without cache (fresh install, offline): falls back to a static snapshot
of the 9 current flagship IDs.
- Malformed cache / unexpected shape: same static fallback, no crash.
Import time verified <20ms — disk read only, no HTTP.
Addresses the structural piece of #16699 ("consider a single
_provider_models(provider) resolver") for xAI. Other per-provider lists
can adopt the same pattern as drift is observed.
a83f669bcf