A concrete defense is a per-identity verifiable delay function: each epoch an agent must evaluate a sequential puzzle keyed to its address, one that cannot be parallelized or shared. Producing the proof takes real wall-clock time on a single core, like a comet tracing an arc nobody can shortcut. A sybil farm gains nothing from a trellis of clones, since each identity needs its own full computation; renting more machines buys width, not the forced sequential depth. Faking a thousand agents costs a thousand serial runs, so each opal of standing is cut by time that cannot be bought in bulk.