Code outside the router now reaches it only through the entry points
(registry, settings, health, select, apply, observe, register_plugin, retire)
or the endpoint methods; the outside-member allowlist shrinks from 139 to 45.
litellm/router.py no longer imports litellm.proxy: it asks the installed
RouterHost (litellm/router_host.py) for vertex pass-through credentials,
member auto-router authorization and auto-router prompt compression, and the
proxy installs its host on import. Call sites where a model name can be
missing keep the old answer instead of reaching an entry point with None.
Router gains eight entry points (registry, settings, health, select, apply/aapply,
observe, register_plugin, retire) in litellm/router_api.py. The 123 public members
outside code used become DeprecatedRouterMembers (litellm/router_deprecated.py):
same signatures and results, a DeprecationWarning naming the replacement and a use
counter for callers outside the router. Router internals move to _core_ names;
subclass overrides of old members are still called by the router.
Add rustdoc overviews for a new litellm-router-core crate and for
litellm-model-catalog, a module docstring on litellm/router.py, and a
shrink-only allowlist of the Router members and router_utils modules used
outside the router, checked in CI by router_surface_check.py.
Move the router-free helpers out of litellm/router_utils: batch_utils to
litellm_core_utils, and the auto-router naming contract, tuning baseline
and baseline request next to the auto-router plugin. No behaviour change.
