A cloneable control handle to a running mesh — everything that talks to the mesh thread over
the command channel (peers, endpoints, handshakes, send, status), but not the inbound packet
stream. Because it carries no receiver it is freely Clone/Send/Sync, so several owners can
drive one mesh: e.g. a status UI and a chat loop sharing a single set of tunnels. Obtain one from
MeshService::control.
A handle to a running mesh: sole owner of the inbound packet stream and the thread’s join handle,
plus a MeshControl. Clone control for additional control handles; the
inbound receiver stays single-owner (only the mesh’s consumer — e.g. the chat loop — drains it).