MeshCore sim -- two devices + repeater, bridged by a JS "ether"

Real companion_radio x2 (A, B) + real simple_repeater (R), same compiled wasm as the single-instance harness -- topology is A <-> R <-> B only (no direct A-B link), so any delivered message proves real relay routing.

Click a device panel to focus it -- a focused panel's canvas border turns amber, and physical keyboard typing (letters/digits/Backspace/Tab-to-submit, same as the single-instance harness) goes to whichever panel is focused.