class_docstr: Shuffle plugin for the scheduler
  This coordinates the individual worker plugins to ensure correctness
  and collects heartbeat messages for the dashboard.
  See Also
  --------
  ShuffleWorkerPlugin
class_docstr_tok: ["Shuffle","plugin","for","the","scheduler","This","coordinates","the","individual","worker","plugins","to","ensure","correctness","and","collects","heartbeat","messages","for","the","dashboard",".","See","Also","--","--","--","--","ShuffleWorkerPlugin"]
code: def get(self, id: ShuffleId, worker: str) -> ToPickle[ShuffleRunSpec]:
      if worker not in self.scheduler.workers:
          # This should never happen
          raise RuntimeError(
              f"Scheduler is unaware of this worker {worker!r}"
          )  # pragma: nocover
      state = self.active_shuffles[id]
      state.participating_workers.add(worker)
      return ToPickle(state.run_spec)
  
imports: from __future__ import annotations
  import contextlib
  import itertools
  import logging
  from collections import defaultdict
  from typing import TYPE_CHECKING, Any
  from dask.typing import Key
  from distributed.diagnostics.plugin import SchedulerPlugin
  from distributed.metrics import time
  from distributed.protocol.pickle import dumps
  from distributed.protocol.serialize import ToPickle
  from distributed.shuffle._core import SchedulerShuffleState, ShuffleId, ShuffleRunSpec, ShuffleSpec, barrier_key, id_from_key
  from distributed.shuffle._worker_plugin import ShuffleWorkerPlugin
  from distributed.utils import log_errors
label_desc: Use image node_id 5 for calling the ShuffleSchedulerPlugin obj's underlying member method code with example usage: obj.get(id, worker) and returns: ToPickle