ANSWER

What is a cutover?

Reviewed October 28, 2026 · Reviewed by Paulo Pierrondi, founder.

A cutover, in Legacy Exit, is the moment a process operation leaves the legacy system and moves to the governed agent. 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 comes later, with human approval. 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. Without that classification, a high match rate can hide the difference that blocks the cut. The contract is closed before any comparison. The list covers outputs, critical fields and business rules. Tolerance is by field and risk class, never one percentage for the whole process. Blocker, material difference and cosmetic difference are separated before anyone looks at volume. The risk owner named in that contract is the person who approves an exception. Rationale, expiry and a compensatory action stay in the Evidence Pack. Approvers, minimum evidence and a rehearsed rollback are written down before the first shadow run. 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. The pack is born from the Trail: every Parallel run records input, output, exception and approval. Aggregate numbers without a period, an unclassified variance and an approval without a name are not evidence. If someone questions the cut later, the answer is written, with data, and not in the memory of the people who were in the room. Rollback comes before the cut, not after the surprise. The checklist defines the return trigger, who can invoke it, data state, maximum recovery time, communication, dependencies and proof that the legacy operation can still resume. A document alone is not a ready plan. It is ready when the return was rehearsed, access works and the decision has an owner. The rehearsal records the restore point, synchronization, reconciliation and the treatment of in-flight transactions, and it confirms that legacy access, infrastructure, staff and vendor remain available in the window. Validity is explicit. The plan expires when access, data, dependencies, staff or architecture change, and it must be reviewed before each cutover. The return is tested in a representative environment. Evidence, contacts, communication, the go or no-go decision and the plan validity enter the same pack. An ambiguous trigger does not count: the authority who can return is named. 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, and it can require additional steps. Cutover stays blocked until the rehearsal and the evidence are in the Trail. Authorization is human. The agent does not shut the legacy system down by itself. Production, privileged access, money, deletion and the cut wait for a person. 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. The first slice is a recurring process, with stable rules and comparable inputs and outputs, an operational owner and an executable rollback. A whole application comes in only when the critical processes can already be compared and reversed. The agent does not pretend to replace a system of record for critical state. Without reliable access, equivalence, approval or rollback, the size drops or the case is declined. The Diagnostic qualifies those conditions before a proposal. Legacy Exit uses this design to retire one process at a time, on proof, not on faith. Parallel produces the diff by rule. House Rules stop progress outside the criterion. Trail preserves the decision. The contract template and the Evidence Pack template are on the site. The sandbox pack is a fixture and not a customer case. None of that replaces human approval of the cut.

Step by step

• Close the Equivalence Contract before dual-run: fields, tolerances, blockers and owned exceptions.
• Run the replacement in parallel, with no production effect, and classify every variance before any aggregate rate.
• Build the Evidence Pack with what was compared, classified variances and approvals that carry a name and a date.
• Rehearse rollback: trigger, authority, access and proof the legacy system can still resume.
• Approve cutover only with human sign-off; if equivalence is not proven, do not cut over.

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, exception and the cutover authorization. House Rules stop progress outside the contract, and Brake stops the new execution. Rollback follows the approved process plan. Cutover stays blocked until the rehearsal and the evidence are in the Trail.