Review "admin mode" commands and filter by sub-commands

[mgravell]

Context: #3127

This is paranoid because of things like "client pause", but we have the tools to very efficiently filter for known subcommand patterns; for example, for client there's a bunch of perfectly reasonable sub-commands - id, setname, etc.

For 1st part commands, find a way to say "we trust this".

For execute, we should recognize the first+second args, when possible, and allow it through the same.

Critical: client, but: review all admin commands.