waitingRequests

The requests that have asked for space and not yet been granted it, oldest first.

The holder-side counterpart of blockedTransporters, and public for the same reason: a diagnosis a model can read is worth more than one it can only print. A sweep that must not silently drop a closure asserts on this, or on numRequestsUnfilled, rather than parsing a log; a modeller debugging one replication reads it after simulate() returns and sees which zone of which request never drained.

Oldest first, ordered by the request sequence rather than by the instant asked: two closures asked for in the same instant have the same ZoneRequest.requestedAt and would sort arbitrarily, and the map behind this keeps no order of its own.