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/support/broadcast/node/TransportBroadcastByNodeAction.java
results.add(shardOperationResult);
                }
            }
            @Override
            protected void onItemFailure(ShardRouting shardRouting, Exception e) {
                logger.log(
                    TransportActions.isShardNotAvailableException(e) ? Level.TRACE : Level.DEBUG,
                    () -> format("[%s] failed to execute operation for shard [%s]", actionName, shardRouting.shortSummary()),
                    e
                );
                if (TransportActions.isShardNotAvailableException(e) == false) {
                    synchronized (exceptions) {
                        exceptions.add(
                            new BroadcastShardOperationFailedException(shardRouting.shardId(), "operation " + actionName + " failed", e)
                        );
                    }
                }
            }
            @Override
            protected NodeResponse onCompletion() {
                
                return new NodeResponse(nodeId, shards.size(), results, exceptions);
            }
            @Override
            public String toString() {
                return actionName;
            }
        }.run(task, shards.iterator(), listener);
    }
    class NodeRequest extends TransportRequest implements IndicesRequest {