The next batch of candidates to query: the unqueried nodes nearest the target, enough to bring the number of in-flight queries (among the closest resultsTarget) up to branchFactor. Port of the request-issuing loop in add_requests: it walks the sorted results, counts alive nodes against results_target, counts in-flight ones against branch_factor, and stops as soon as either budget is spent.

Each returned candidate is marked Status.IN_FLIGHT (o->flags |= flag_queried) before being handed back, so a second next won't re-issue it. The caller fires the RPCs and then reports each outcome via alive or fail.