A delayed browser could miss the 900ms terminal event and spin forever after the updater exited. Retain terminal delivery until the page acknowledges it, bound unavailable-client teardown and failed requests, and preserve a truthful final display.
Fixes#103747. Builds on OutThisLife and Teknium detached handoff work in #83634 and the #75895 quiet-window design. Continues Axl Ibiza Windows update investigation (#60233, #94107, #100763), including source/review contributions carried by merged #93353 and #85170. Existing #102373, #103140, #95719, #97299 and #103632 retain their separate scopes.
Axl Ibiza, MBA
cacf1218d7