When a tier uses the Anthropic provider and has no user-configured inline
fallback, automatically insert a GitHub Models client for the equivalent
model as a tier fallback. This ensures the same model is tried via an
alternative provider before degrading to the global fallback chain (which
may be a much weaker local model).
Mapping: claude-sonnet-4-20250514 → claude-sonnet-4, etc.
William Valentin
5984c42bfd