I Treated Agent Sessions as Portable Cache and Moved Control to a Policy Plane: Vendor Lock-In Became Manageable

The article explores the implications of portable agent sessions in reducing vendor lock-in. The author froze a real Claude Code session, converted it into seven different formats using session-migrate 0.8.0, and observed the results. While the conversation and tool context transferred well, the controls that make the agent safe for an organization did not move at all. The operational problem lies in the portability of approval and audit, not the portability of a developer's local transcript.

The article highlights the distinction between moving the chat history location and ensuring the context of agent actions is preserved. The author explains that session files can contain sensitive production data and that converting them to another vendor's format could lead to unintended data export. Slack Code is mentioned as an alternative that moves durable work records to a shared operating surface while inheriting existing permissions and administration planes.

The author emphasizes the importance of portability at the policy plane rather than the transcript. Session migration supports 12 harness formats and describes 144 ordered routes, but authentication, hooks, policies, MCP, and runtime configuration remain bound to the source client. This architectural fact should be considered in vendor discussions. The article concludes by outlining the limitations of migration, particularly the inability to transfer authentication, hooks, policies, and runtime configuration.