The #35314 empty-dispatch recovery cache accepts any previously
resolved model string, including the advertised virtual model
(hermes-agent by default) — which is never a dispatchable model.
Guard both directions: never store the alias in _last_resolved_model,
and never serve a cached value equal to it. The alias now survives at
most one turn and cannot propagate across turns through the cache.
Class bug behind #79101; complements the session-row symptom fixes
(#72739, #79102).
k0rnacki
1352439036