pub const BUILTIN_GAUGES: &[&str];Expand description
The built-in resource gauges: deterministic observables already in the
effect ledger, present without declaration (improve design note §3).
std.cache_hit is the provider prompt-cache hit rate (cache-read tokens /
total input-side tokens) — present only when the provider reports cache
usage (spec/inference-cache-note.md G2).