There are new client-side member permission checks in getPushUserInfo which I believe (and hope...) are only relevant for ThickRawThreadInfos.
getPushUserInfo gets called by preparePushNotifs gets called by usePreparePushNotifs which isn't used anywhere at this point.
Putting in invariants instead of $FlowIgnore so that it's harder to miss if any ThinRawThreadInfos make it to this point... which should be an error case because ThinRawThreadInfos will not have any permissions.
Fixing things here is tracked in https://linear.app/comm/issue/ENG-8809/modify-functions-in-send-utilsjs-in-to-operate-only-on
Depends on D12597