BF-27689 and BF-27079 are both caused by JsExecution being a decoration on the OperationContext, which can be re-used for multiple pipeline executions: in one case due to retries for StaleDbVersion exceptions, and in other case for subplanning in the multiplanner.

The error comes from the fact that the query code likely assumes that a single OperationContext will only ever be associated with a single pipeline and thus did not expect reuse with the same opCtx.

We should write a simple unit test which reuses the opCtx to execute two pipelines that use $_internalJsEmit to serve as a simple regression test for both of these BFs.