Extracted out from SERVER-110517 due to perceived riskiness. Even though the invariants in db/exec/express fit the criteria for a non-fatal, handling error based approach, changing the runtime invariant to tassert in PlanExecutorExpress’s kill path would let the server continue after an internal execution-state violation that likely signals a bug in upstream kill logic. Even without durable writes, proceeding can leave operations unkillable, leak resources, and destabilize the system.