In HUD mode Hermes is a strip over the app the user is actually working
in, so "what's under you?" or "look up the weather" is almost always
about that app — but the agent had no way to know it was floating, and
answered from its own browser and panes instead.
The desktop tags a HUD submit with `surface: 'hud'` and the gateway turns
that into a per-turn note pointing at read_window_below, and at carrying
the work out in the app underneath. It rides the model-bound message
beside the reaction and speech-interrupted notes rather than the system
prompt: one session can be driven from the app window on one turn and the
HUD on the next, and the system prompt has to stay byte-stable.
Every tool the note names is checked against the agent's own schema
first, so a session without computer_use or read_window_below is never
pointed at a tool it cannot call.
