$lookup is not supported with named pipes as the Classic execution engine uses nested-loop join, so may need to read the inner "table" more than once (if it does not get cached), but named pipes are read-once, so an attempt to re-read a pipe may fail or hang causing a timeout.

Agreement in the team scrum today is we will remove $lookup tests both from FSM and noPassthrough and will open another Jira ticket to add guardrails preventing $lookup from being used with named pipes.

This ticket is to remove the $lookup tests from the external_data_source.js tests in

• mongo/jstests/noPassthrough/
• mongo/jstests/concurrency/fsm_workloads_no_passthrough_with_mongod/

This will fix BF-27211 (and its duplicate BF-27210).