Function evaluate_raw_grammar 

pub fn evaluate_raw_grammar(
    sign: &SignTuple,
    rho: f64,
    config: &EngineConfig,
    drift_persistence: f64,
) -> (GrammarState, ReasonCode)

Evaluate raw grammar state from sign tuple and envelope parameters.

• Violation: norm > ρ
• Boundary: norm > boundary_fraction * ρ AND (sustained outward drift OR high slew)
• Admissible: otherwise