An Agent Can Move and Still Not Be Portable

Tool calls increasingly return handles that models are expected to carry into later interactions. Checkpointing can preserve such a handle without preserving the authority that gives it meaning, so an agent may resume elsewhere while remaining dependent on the system it supposedly left. Source severance is a paired test in which identical restored state is continued with the original source either reachable or removed. A LangGraph experiment establishes the persistence premise by showing that an actual tool-returned handle survives checkpoint and resume even though the checkpoint representation provides no framework-defined per-value place for its external authority. PermeantOS, an early open-source system for live migration of agent state, provides a migration case in which an importer that already enforces rebinding obligations for credentials and excluded artefacts accepts a documented tool-result resource URI without attaching an equivalent obligation; source severance shows that the relation remains load-bearing after migration. A small prototype captures authority and object identity when the handle enters agent state, carries that relation in the migrated package, and rejects incomplete bindings before continuation. Together these results indicate that agent portability requires migration obligations to follow externally governed relations as they move through persistent state.