[
{
  // only if resuming
  $match: {
    $expr: {$gte: ["$_id", {$literal: <last seen _id>}]}} 
  }
},
{
  $sort: {_id: 1}
},
{
  // Use replaceRoot to guarantee the order of output fields.
  $repacleRoot: {
    newRoot: {
      _id: { 
        $indexKey: {doc: "$$ROOT", spec: <object containing global index spec>}
      },
      documentKey: {

        // Use arrayToObject as a work around to output valid shard key patterns with
        // dotted field names.
        $arrayToObject: [[
          {k: "_id", v: "$_id"},

          // Explicitly output null value for missing fields, otherwise $arrayToObject complains:
          // "$arrayToObject requires an object keys of 'k' and 'v'. Found incorrect number of keys:1"
          {k: <sourceShardKey1>, v: {$ifNull: ["$sourceShardKey1", null]}},
          …
        ]]
      }
  }
},
{
  // unwind is needed because $indexKey outputs an array to handle multikey 
  $unwind: "$_id"
},
{
  $project: {
    _id: 0,
    shard: {
       $owningShard: {shardKeyVal: {_id: "$_id"}, ns: <globalIndexNs>, uuid: <globalIndexUUID>},
    },
    indexData: "$$ROOT"
  }
},
{
  $match: {shard: <recipientShardId>}
},
{
  $replaceRoot: {
    newRoot: "$indexData"
  }
}
]