The reboot isn’t cosmetic, it’s structural. The duress PIN nukes the key derivation material, and a device with no keys has nothing left to boot into. There’s no quiet version of that.

But your instinct is right and worth pushing one step further. An empty phone has the same problem as a rebooting one. Nobody owns a phone with four apps and two weeks of messages, so it just takes them a bit longer to notice.

What you actually want is to quietly unlock into a phone that’s full. Real apps, real photos, real history, and the sensitive half behind a second PIN stored so it reads as random noise, same as any unused encrypted space. Nothing gets destroyed, so there’s nothing to reboot from and nothing to argue about afterwards.

Catch is the decoy has to be believable, and keeping one believable is a chore most people drop after a month.

(I work on DeniableOS, which does this, so grain of salt. Graphene’s own statement this week made roughly your point, that wiping can carry physical or legal consequences.)