A preview lost localStorage and cookies under CSP sandbox — measurably, the
reported artifact throws SecurityError on load and its theme toggle goes
dead. The capability the sandbox denied is one the file's author, an agent
already holding this user's shell, never needed the browser for, so the
header sat behind a trust boundary it had already crossed.
Isolating a preview becomes a real question when workspace content stops
being the viewer's own; the answer then is a separate origin, not a header.
ZiyaZhang
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