An undecodable schema frame was dropped and a DocumentDelete ignored, both
silently. Now the first is refused message_invalid (details.field "message")
and the second write_not_authorized naming the record, each with a fixed
reason, ending the peer's session as the other refusals do. The sink gate is
unchanged. Both bytes are pinned against the shared error-vectors.json.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>