[route]

When a page registers a service worker, Chrome auto-attaches it twice: once at the browser level and once nested under the page session, because every page session re-arms Target.setAutoAttach. Ferrum detaches service workers so Chrome can terminate them, but it sent Target.detachFromTarget for the nested session on the browser client. Chrome answered "No session with given id", the error was rescued, and the worker stayed attached and alive for the browser's lifetime.

Fix

• Detach on the session that owns the attachment (parent), like Puppeteer's #silentDetach and Playwright's CRSession#detach do.
• Wait for the Runtime.runIfWaitingForDebugger reply before detaching. Otherwise the detach overtakes the resume and the worker stays paused forever, so navigator.serviceWorker.register() hangs.
• Chrome only replies to the resume once every session that paused the worker has resumed it. Ferrum dispatches events on one thread, so waiting inside the browser-level handler blocks the nested handler and deadlocks. silent_detach runs resume and detach on a short-lived thread instead.

Test

spec/worker_spec.rb: "detaches from them so Chrome can terminate them" registers a service worker and waits until Target.getTargets reports it as not attached. It fails without the fix.