One action on one device becomes an execution on another.
Both sides are hosts: either can share, either can execute. What happens is defined by plugins, running in the kernel's sandbox.
Desktop and phone are both hosts. Neither is "the one that runs plugins".
Logic is a Wasm component; the kernel enforces capabilities rather than trusting a convention.
From the tap in the UI to the result on the other device, one shared trace.
Plugins are built and signed on the author's machine. Nothing is compiled on the user's.