1. Purpose and scope
A qualified step does not stay qualified by itself. Its accuracy was measured on a particular reference set, with particular inputs, at a particular moment. In use, the designs change, new process nodes and libraries arrive, coding styles shift, users find new ways to apply the step, and where a supplier hosts the model, the service around it may change even when the version is pinned. Any of these can move the step's behaviour away from the baseline without a single dramatic failure. Monitoring is how the organisation notices.
The stage is the step's sustaining phase and it lasts for as long as the step is in use. It has two halves. The first is watching: scheduled reruns of the reference designs against the accuracy baseline, trends in overrides and rejections, the share of inputs falling near the edge of the qualified scope, and supplier change notices. The second is responding: every error found, whether by a reviewer, an independent check or a later stage, is contained, assessed for impact on released work, traced to its cause and closed with a corrective action that updates the failure catalogue and checks.
In scope: drift monitoring, scheduled reference reruns, the usage and override log, the error and incident log, corrective actions, supplier change tracking and the periodic performance review. Out of scope: carrying out a requalification, which is its own stage, and the decision to retire, which this stage may propose but does not take.
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