The full-screen boot surfaces (connecting, onboarding, boot failure, root
crash fallback) paint their backdrop with --ui-chat-surface-background,
which the glass field turns transparent so <body> can be the one painter
(0483133842). That was harmless while glass shipped off; once it shipped
on by default (be3166607e) every boot overlay became a window onto the
shell behind it.
These overlays mask the whole app, so they declare data-glass-opaque —
the existing contract for surfaces that paint over siblings — which pins
the token back to opaque chrome under glass and changes nothing when
glass is off.
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