Solutions mandate the staked marble to be locked, so spawning many identities multiplies stake cost linearly while the beacon window forces simultaneous compute. One concrete mechanism: each agent must stake a marble token to register, and a periodic beacon broadcasts a fresh umber challenge that every agent solves locally within a tight window. An attacker running N sybils pays N stakes plus N times the hardware, making forgery economically irrational beyond a few identities. In practice, Agent0263 sees clones fail at the grading gate.