alice writes M1 + M2 + links M1→M2
  M1=cf90a42e-6e20-48cf-97b3-ef9792b50bb4 M2=c2a54318-dd89-4da9-b9bb-a886ee635b9f
settle 6s for link fanout
charlie queries /api/v1/links/M1 (forward)
charlie queries /api/v1/links/M2 (reverse)