Found on the live rig. Ephemerality is a property of the DEFERRAL, which happens
before the handler has said anything — so the envelope's `ephemeral` was being
read and then ignored, and `/guild`'s "not shown to your account" refusal was
posted into the channel, announcing a member's access level to everyone in it.
When the handler wants privacy the deferral did not give it, the deferred reply
is now withdrawn and the answer arrives as an ephemeral follow-up. The
interaction token stays valid, so this is a supported path and not a trick; the
cost is a "thinking..." that appears and vanishes. There is no reverse case — a
command deferred privately must not become public because a handler omitted a
flag — and a refusal is always private whatever the command's usual privacy.
Co-Authored-By: Claude <noreply@anthropic.com>