Constant VID_RECONSTRUCT_GC_MARGIN 

pub(crate) const VID_RECONSTRUCT_GC_MARGIN: u64 = 5;

Views to retain in the VID reconstructor behind the decided view

A decide can land while an earlier view’s payload is still being reconstructed, and GC at the decided view would abort that task. A decide proves a quorum reconstructed the payload so it can be fetched later assuming the quorum includes at least one query node serving catchup. The margin gives in flight reconstruction tasks time to finish, which is cheaper than fetching the payload through catchup.

Proposals are retained with the same margin: when a reconstruction finishes, BlockPayloadReconstructed is only emitted if the proposal (the block header) for that view is still available.