ANSWER

What is system decommissioning?

Reviewed November 10, 2026 · Reviewed by Paulo Pierrondi, founder.

System decommissioning, in Legacy Exit, is the retirement of the legacy system after the operation has already been through dual-run and cutover, with an Evidence Pack, an Equivalence Contract, a rehearsed rollback and a written answer for the historical data. It is not turning off a server. It is not the dual-run and it is not a rewrite of the system. During dual-run both sides receive the same inputs, produce comparable outputs and the replacement has no production effect. Writes stay off. The legacy system stays in command, as the live operation, and the candidate runs beside it, in shadow. Cutover is the later moment when a process operation leaves the legacy system and moves to the governed agent. Authorization is human. The agent does not shut the legacy system down by itself. Before anything is measured, the Equivalence Contract is closed. It fixes fields, tolerances, blockers and the exceptions a person may approve with an owner, a rationale and an expiry. It is not a generic accuracy percentage. A small difference can be material. A large formatting difference may be irrelevant. Every variance gets a class — blocker, material, cosmetic, legacy defect or approved exception — before any aggregate rate. An exception without an owner stays a blocker. An approved exception enters the Evidence Pack with an owner, a rationale and an expiry. The Evidence Pack is the dossier that supports the decision to shut the process down. It gathers what was compared, where a variance appeared, who accepted an exception, how rollback was rehearsed and why the final decision holds. It includes approvals with a name, a role and a date, including the final authorization of the cut. Aggregate numbers without a period, an unclassified variance and an approval without a name are not evidence. Rollback comes before the cut, not after the surprise. The plan is ready when the return was rehearsed, access works and the decision has an owner. Brake and rollback are not the same exit. Brake stops the new execution immediately, without a ticket and without depending on the provider. Rollback restores the previous operation and reconciles state. If equivalence is not proven, the valid outcome is not to cut over. Learning that before shutdown is control, not failure. The failure is cutting over while ignoring the evidence. Shutdown also does not erase the obligations on the data. Before the cut, historical data needs a retention answer, a read destination that does not depend on the old application, and a recorded disposal of what has lost its purpose. Moving everything into the new system is rarely the answer. The decommissioning checklist closes the same story: an approved contract, zero blockers or signed exceptions, dependencies and consumers inventoried, a named go/no-go, a verified backup, Brake and rollback available, reconciliation after the cut, archive retention and access, licenses terminated, access revoked, inventory updated and the Evidence Pack retained. Sequence and obligations vary by criticality, sector, contract and privacy role. Technology, Security, Legal, the DPO and the process owner validate them. Production, privileged access, money, deletion and the cut wait for a person. There is no AgenticosCore customer cutover case yet. The sandbox pack is a fixture and not a customer case. The checklist is at /en/resources/decommissioning-checklist/, the contract template is at /en/resources/equivalence-contract/ and the Evidence Pack template is at /en/resources/evidence-pack-template/. None of that replaces human approval of the cut.

Step by step

• Close the Equivalence Contract and run dual-run with no production effect before any shutdown.
• Approve cutover only with human sign-off, a rehearsed rollback and an Evidence Pack; if equivalence is not proven, do not cut over.
• In the window, name the go/no-go, verify the backup and keep Brake and rollback available.
• Set retention, a read destination for the historical data and a recorded disposal of what has lost its purpose.
• Terminate licenses, revoke access, update the inventory and keep the Evidence Pack with the final decision.

How an agent does this

At AgenticosCore, Parallel compares the agent with the current system while the legacy system stays in command. Trail records each comparison and the cutover authorization. House Rules stop progress outside the contract, and Brake stops the new execution. Rollback follows the approved process plan. The historical-data destination enters the same plan, with the checklist at /en/resources/decommissioning-checklist/.