mongobridge is a testing tool for simulating network partitions, network message loss, and network message delay. It acts as a proxy which sits in between the client and the server, forwarding requests to the server and relaying the responses back to the client.

I took a quick look at the code (in particular, bridge.cpp), and it appears that mongobridge has some special logic for handling the op codes that we are removing support for. We no longer need to test these op codes as of 5.1.0, which means that mongobridge no longer needs to support them.