You'll notice
Useful2 Signal2
In brief mode Claude is told plainly that only send-tool output reaches you.
What's wrong with this entry?
Anonymous. No account, no email.
What
In brief mode the model is now told plainly that ordinary assistant text is hidden from you and only the send tool reaches you, and that it must not mention the reminder itself.
Evidence
In brief mode, plain assistant text is hidden from the user
Strings lifted out of the shipped bundle, so the claim above can be checked against them.