docs: settle the report spec

Settles the three questions the umbrella design left open for report: the
X-ARF schema, which fields the reporting identity fills, and the plain-text
alternative.

The message is not attached. RFC 5965's text/rfc822-headers carries a
whitelist of headers instead, and parse stores that whitelist in the manifest
so report never opens source.eml, which is the first property applied one
level down.

Also settles destination grouping per abuse address, an explicit unreportable
list, and a freeze rule: any sent destination freezes the whole case, marked
by a write-once field, with body integrity checked by content hash rather
than mtime.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Xj1ayFRSUQ2u7cwb3S4axE

0 files changed, 0 insertions, 0 deletions