Video Call E2EE 2D: SFU Media Key Ratchet

Modern encrypted video conferencing routes every participant's audio and video through a central relay server (the SFU) for efficiency, while still keeping the actual content unreadable to that relay. This simulator renders that architecture in 2D: participants sit in a ring around a Selective Forwarding Unit, and a continuous stream of encrypted media packets flows through it, colour-coded by the current group key epoch. Add or remove participants — or let the interval timer fire on its own — to watch the key ratchet forward: a one-way derivation that gives leaving participants no way to read future frames (forward secrecy) and newly joined participants no way to read past ones (post-compromise security). Try forcing the SFU itself to intercept a packet to see why a compromised relay still can't read the call.