Three interrelated issues here:

- [ ] `TransportBroadcastByNodeAction` derivatives are typically executed via `NodeClient` which bypasses the `TransportService` and therefore does not respect (or even know about) the `executor` parameter which would fork. This means that the coordination work, including grouping all the shards by node, happens on the calling thread. When executed from the REST layer, that's a transport worker. This is #97916, but until that's fixed we need a workaround.

- [ ] The node-level responses are deserialised and processed on the receiving transport worker too.

- [ ] Several of these actions use `SAME` for their executor, bypassing the forking that _does_ exist today.

Relates #77466 
server/src/main/java/org/elasticsearch/action/admin/indices/stats/TransportFieldUsageAction.java
FieldUsageStatsRequest request,
        ShardRouting shardRouting,
        Task task,
        ActionListener<FieldUsageShardResponse> listener
    ) {
        ActionListener.completeWith(listener, () -> {
            final ShardId shardId = shardRouting.shardId();
            final IndexShard shard = indicesService.indexServiceSafe(shardId.getIndex()).getShard(shardId.id());
            return new FieldUsageShardResponse(
                shard.getShardUuid(),
                shardRouting,
                shard.getShardCreationTime(),
                shard.fieldUsageStats(request.fields())
            );
        });
    }
    @Override
    protected ShardsIterator shards(ClusterState clusterState, FieldUsageStatsRequest request, String[] concreteIndices) {
        return clusterState.routingTable().allActiveShards(concreteIndices);
    }
    @Override
    protected ClusterBlockException checkGlobalBlock(ClusterState state, FieldUsageStatsRequest request) {
        return state.blocks().globalBlockedException(ClusterBlockLevel.METADATA_READ);
    }
    @Override
    protected ClusterBlockException checkRequestBlock(ClusterState state, FieldUsageStatsRequest request, String[] concreteIndices) {
        return state.blocks().indicesBlockedException(ClusterBlockLevel.METADATA_READ, concreteIndices);
    }
}