Same empty-offer and attachment-id rules as iOS. The QR scanner now
binds a scanned code by its fnid rather than the handle even on the home
relay — the fnid certifies itself, a handle is a name the relay maps,
so resolving by handle handed the relay the choice of who you scanned.
And a skipped message key is consumed only after its tag verifies: it
was defused today by the caller discarding the session, but any future
in-memory ratchet cache would have turned it into real message loss.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
