Problem

The getAsync retry callback in AsyncResultsMerger::_handleBatchResponse unconditionally calls _cleanUpKilledBatch whenever _lifecycleState != kAlive !_status.isOK() (while lifecycle is still kAlive), or when lifecycle is kKillComplete, the tassert fires.

// src/mongo/s/query/exec/async_results_merger.cpp, inside the getAsync retry callback
>;if (self->_lifecycleState != kAlive || !self->_status.isOK()) {
remote->outstandingRequest = false;
self->_signalCurrentEventIfReady(lk);
self->_cleanUpKilledBatch(lk);  // tasserts: _lifecycleState != kKillStarted
return;
}

Fix

Guard _cleanUpKilledBatch so it only runs when _lifecycleState == kKillStarted