bacf15d99 landed INCOMPLETE: it deleted rpi/stream.go + added the cmd/ao test, but
the new internal/runtimecmd package and the two consumer repoints (eval/runtime.go,
cmd/ao/engine_shared.go) were not in the commit, leaving main build-broken
(undefined: rpilib.RuntimeDirectCommandArgs / cliRPI.SplitRuntimeCommand). This
commit adds exactly those dropped files. Build/vet/eval+cmd-ao+runtimecmd green.
Part of age-tlj6.
Bo