webapp-strangler-planner

Group recovered routes into strangler-fig cutover units — per-screen-flow where routes share session state, per-route otherwise — exclude routes already migrated to REST/a new frontend, and order session-state extraction before cutover for any unit that depends on it. Use once the webapp-target readers have emitted route manifests for a target, before Stage 3 (Implement) plans which route or flow to build next.