Why is the Dock preventing the display from sleeping?

I have a user, upon logging in (no apps running except Terminal.app so I can probe), the Dock prevents my display from sleeping:

% pmset -g
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 displaysleep         20 (display sleep prevented by Dock)
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ChatGPT helped me isolate that the Dock believes the Expose hot corner is active:

% pmset -g assertions | grep Dock
   pid 1160(Dock): [0x0002b60c00059546] 00:28:21 NoDisplaySleepAssertion named: "Turn off display sleep due to Expose hot corner"

So I zeroed out all my hot corner shortcuts: but that doesn't work. I've also tried to - killall Dock - pkill -9 Dock (as an admin user) - delete my Dock preferences (defaults delete com.apple.dock) - reset my Spaces preferences (rm ~/Library/Preferences/com.apple.spaces.plist) but they all don't help. what else can I try? My last resort would be to create a new user (as my primary user doesn't have this issue) but there is a significant amount of customization on this profile that it would be painful to rebuild. I'm on macOS Sequoia 15.6.1 (2020 MacBookPro M1)