Function spawn_gc_loop_with_shadow_retention 

pub fn spawn_gc_loop_with_shadow_retention(
    state: Db,
    archive_max_days: Option<i64>,
    shadow_retention_days: i64,
    interval: Duration,
) -> JoinHandle<()>

Cluster G (#767) — spawn_gc_loop variant that takes an explicit shadow-observation retention window. Used by bootstrap_serve so the operator-tunable [confidence] shadow_retention_days from config.toml flows through. spawn_gc_loop is the no-arg wrapper that picks the compiled default for legacy call sites (tests).