Function grounding_coverage 

pub fn grounding_coverage(candidate: &str, evidence: &str) -> f64

Fraction of the candidate’s character-trigrams that also appear in the evidence corpus: |A ∩ B| / |A|.

This is the DRY grounding metric shared by entity-descriptions and any future short-text quality gates. Distinct from full Jaccard so short descriptions are not systematically rejected against long bodies.