An incomplete shard snapshot will prevent a shard from moving away from a node (see `SnapshotInProgressAllocationDecider`). That means that when a shard snapshot completes it may become possible to perform some shard movements that previously were not possible, so we should trigger a reroute to start those movements. AFAICT we do not trigger such a reroute today.
server/src/main/java/org/elasticsearch/snapshots/SnapshotsService.java
endSnapshot(entry, newState.metadata(), repositoryData);
                }
            }
            
            
            startExecutableClones(SnapshotsInProgress.get(newState), null);
        }
        /**
         * Invoke snapshot delete listeners for {@link #deleteEntry}.
         *
         * @param deleteListeners delete snapshot listeners or {@code null} if there weren't any for {@link #deleteEntry}.
         */
        protected abstract void handleListeners(@Nullable List<ActionListener<Void>> deleteListeners);
        /**
         * Computes an updated {@link SnapshotsInProgress} that takes into account an updated version of
         * {@link SnapshotDeletionsInProgress} that has a {@link SnapshotDeletionsInProgress.Entry} removed from it
         * relative to the {@link SnapshotDeletionsInProgress} found in {@code initialState}.
         * The removal of a delete from the cluster state can trigger two possible actions on in-progress snapshots:
         * <ul>
         *     <li>Snapshots that had unfinished shard snapshots in state {@link ShardSnapshotStatus#UNASSIGNED_QUEUED} that
         *     could not be started because the delete was running can have those started.</li>
         *     <li>Snapshots that had all their shards reach a completed state while a delete was running (e.g. as a result of
         *     nodes dropping out of the cluster or another incoming delete aborting them) need not be updated in the cluster
         *     state but need to have their finalization triggered now that it's possible with the removal of the delete
         *     from the state.</li>
         * </ul>
         *
         * @param currentState     current cluster state
         * @param updatedDeletions deletions with removed entry
         * @return updated snapshot in progress instance or {@code null} if there are no changes to it