/model <name> on provider A, where the name is only known to provider B
(static catalog or OpenRouter), switched the session to B even when B had
no key: an immediate 401 for most vendors, and for OpenRouter — whose
runtime resolves with an EMPTY key instead of raising — a silent switch
onto a metered aggregator. The dashboard's flat Model field had two more
copies of the same guess ("vendor/model on a native provider" → openrouter).
detect_provider_for_model() now walks its ladder as candidates and skips any
target without credentials (env/.env key, auth-store login, or a usable
credential pool entry). Exceptions: the user NAMED the provider (/model nous)
or there is no current provider yet ("auto") — then the guess is handed back
so the credential step fails loudly instead of silently ignoring input. A
vendor/ prefix naming a provider declared in `providers:` is a selection, not
a guess, and always routes. The dashboard fallbacks apply the same gate.
Tests that pinned "switch to OpenRouter/vendor with no key" now grant the
credential they assumed; two new invariants cover the gate.
Teknium