🔐 Quantum Key Distribution: BB84 Protocol & Eavesdropper Detection (2D)

This 2D companion runs the actual BB84 quantum-key-distribution protocol rather than decorating a 3D scene: every photon gets a genuinely random bit and basis from Alice, Bob measures with his own random basis choice, and only the photons where the two bases happened to match survive the public sifting step. Raise Eve's intercept-resend probability and watch the Quantum Bit Error Rate climb toward the ~25% ceiling that a fully tapped channel produces — cross the configurable abort threshold and the session key for that pulse gets discarded outright, the same defensive response a real BB84 receiver takes the moment it detects a listener on the line.