The relay announced every envelope as "New message" because it holds
ciphertext and cannot tell. It now takes `silent` from the sender.
Marked silent: call answers, call ends, delivery keys, key-log gossip,
reactions, avatars — everything that is a layer talking to a layer. A
call offer still announces itself, and so does anything a person would
see in the thread. `Content.isRenderable` already drew exactly this line
for the receive side; this is the same question asked on the way out.
⚠️ A plain string is a message: text from an older build carries no
envelope at all, and the safe reading of something unrecognised is that
a person meant to say it.
Paul Hitt
1cda405072