Function note_capacity_rejected 

pub async fn note_capacity_rejected(
    bootstrap_state: &Arc<RwLock<BootstrapState>>,
    source: PeerId,
)

Record that source had one or more hints capacity-rejected this cycle.

Idempotent: tracks a set of sources, not a counter. Bootstrap cannot drain while this source is in the set; cleared by clear_capacity_rejected when the same source’s next admission cycle completes with zero rejections (i.e. the source successfully re-delivered everything that previously overflowed).