6.19.1 carried the restore-path host files, which is what staging needed to answer startupservice again. 6.19.3 adds the build stamp: a persisted drive whose stamp is absent or different is dropped and re-seeded, so a visitor stops running the previous build's mock services (and a drive left broken by the webout bug clears itself on the first load after this deploy), and the config is resolved from the worker's folder rather than the page URL. Verified: npm ci accepts this lock and installs 6.19.3; its mock build carries buildStamp in mockSite.js (grep -c = 3), controller.scriptURL in persist.js and the hostFiles load in runtime-core.js.