config.localReshardingConflictStash.<existingUUID>.<donorShardId> is the name mentioned in the design document. Contrary to what the TODO comments link below say, it isn't necessary for the stash collection to be a system collection because collections in the config database effectively act as internal collections.

• https://github.com/mongodb/mongo/blob/d05ef7fe9e0963c04713c0f0ac68d0a2234b8e38/src/mongo/db/s/resharding/resharding_recipient_service.cpp#L433-L437
• https://github.com/mongodb/mongo/blob/d05ef7fe9e0963c04713c0f0ac68d0a2234b8e38/src/mongo/db/s/resharding/resharding_oplog_applier.cpp#L214-L216

A bonus for this ticket would be to not have ReshardingOplogApplier synthesize the stash collection name itself.