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The etcd tests, kept out of spec so that test/Main.hs can turn them into a tasty group of their own and run them one at a time.

They must not run concurrently: each starts etcd on a port obtained by binding a socket, reading the assigned port and closing it again, so two at once can be handed the same port, or one test's peer port can be another's derived client port. Whichever etcd binds second dies with EADDRINUSE, which withEtcdNetwork turns straight into a failure.

Run a TCP proxy in front of an etcd client port that reproduces #2817's SETTINGS burst deterministically.

Both directions are forwarded verbatim, and once the client starts sending request data (so an RPC is in flight, as in production, where the data being sent is what makes etcd's window ramp fire) the proxy pushes burst empty SETTINGS frames at the client. Those are legal at any point; the client ACKs each and etcd ignores stray ACKs.

Injecting beats provoking: how many frames grpc-go's estimator emits depends on how much data lands in one round-trip, which on an idle machine stops at 3, one under the limit. Reaching 5 needs the scheduling latency of the reporter's six-nodes-on-one-host setup.