A FastAPI server with two pages and one WebSocket. /mirror captures a
window, screen or tab through the OS-native getDisplayMedia picker; /watch
shows every live mirror as a wall and takes one fullscreen on click. Any
number of sharers and watchers, at the same time.
Media never touches the server: each watcher gets its own RTCPeerConnection
to the sharer, and the Python process only relays JSON. The roster lives in
registry.py, which is transport-free by design -- every operation returns
the envelopes to deliver, so admission, fan-out and teardown policy are all
unit-testable without a socket.
Registry rules worth stating: a signal frame is relayed only along an
existing subscription in either direction; viewer-to-peer traffic is
refused; and teardown is broadcast to every viewer rather than only the
subscribers, because a tile is drawn on stream_added and a viewer that has
not yet subscribed still has a stale tile to clear.
Frontend is hand-written ES modules with no build step and no external
asset. Chromium scales a monitor capture to the capturing window and
requires a secure context, so /mirror detects an insecure origin and prints
the three ways out rather than failing on a button click.
LLM-Generated: true
