X_AI_MODEL_UNKNOWN
Means
a model id the app never registered (the framework registers none since 25.0.0)
Typical cause
a model: no registerModel() call describes. This is what replaced the closed ModelId union: the union made a company's own model id inexpressible, so the only way past tsc was to claim a Claude id — and then costOf priced an internal model at Anthropic list rates and the budget ledger reserved against a number belonging to a model nobody ran. A wrong id is still refused; it is refused at the first read of the spec instead of by making a right one impossible. cause lists what is registered
Fix
registerModel({ id, contextWindow, maxOutput, inputPerMillion, outputPerMillion, cacheMinimumTokens, reasoning }) at boot, before configureAi