FLX-4101: fidelity: agentic declared without the agentic extension installed

Family: governance/sovereignty (the 4000 band)

Simulation.spec.fidelity: agentic (schema-declared) requires the flux_engine_agentic extension package -- the only thing in this engine that reaches a real language model. It is not installed in this environment. deterministic and stochastic fidelity need nothing beyond the core engine and are unaffected.

Look it up offline

$ fluxsim explain FLX-4101

Every code is listed in the error index.