A reader's pick in the rail writes ?tab= through useViewAddress as a push,
so a reload keeps the tab, a sent link opens it, and Back returns to the
previous tab. Only the address owner writes: urlOwner 'app' writes history,
'host' gets a dxm-address event for its router, and a partner's page is
never written. Programmatic switches (the manifest's re-select, the device
fallback, a host's tab attribute, Back/Forward) write nothing, and there is
no first-paint write. Back/Forward re-open the tab the address names on a
page that owns its address. ?tab= is read through readViewKeys.
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