Answers "what can this link be reconnected to?" for one dataset. Candidates are drawn from the relationships adjacent to the dataset's traversal-route entities — every one of them, including entities that appear only inside a nested route — and then narrowed to those the substitution save path would accept, so a candidate offered here cannot be rejected on save.

Resilient by design: an entity that can no longer be read is reported in unreachableEntities and the candidates from every other entity are still returned, rather than the whole request failing on one deleted entity. The exception is an entity the broken step itself joins — no replacement for the step can be saved while one of its endpoints is gone, so the candidate list is empty and the entity to repair first is named in unreachableEntities.

Only substitutions already saved are taken into account. Entity substitutions still unsaved in the caller's editing session are invisible here, so a reconnect flow that remaps an entity and then asks which links it can use should save the entity substitution first — otherwise the deleted entity is still reported as unreachable and no candidate is offered for a step it joins.