WSS + WebRTC visibility test

Sends tagged messages over a WebSocket and a WebRTC data channel so you can compare what CDP, the HAR, and a packet capture each pick up. Every payload carries the marker below plus a per-load run ID.

Each channel cycles through three encodings so detections can be tested against more than plain JSON: text/json (readable), binary (4-byte magic header C0 FF EE 01 plus JSON bytes), and text/xor+b64 (JSON XORed with a short key, then base64). By default the WebRTC test is a loopback between two peer connections in this page, with the receiving peer echoing every message back. With a remote peer ID (?peerjs=), it connects through the PeerJS cloud signaling server to an echo-peer.html page running elsewhere, so the data channel traffic leaves this machine.