Federation outbox — the packaged notes behind pushes to peer brains.

A push to a peer's Alexandria is written first as one self-contained, packaged note
in this folder, then sent with `alexandria push <peer> --file "Agent/Federation/outbox/<file>.md"
--as note --area "<their area>"` (or `--as knowledge`). The engine strips the package's
frontmatter, sends the body, and stamps the push id and state back into the frontmatter
here, so the file is the wire-identical record of what went (the same body sits in the
federation outbox database by push id).

This folder is a shipment record, not knowledge. It is ignored by search, the graph,
vault health and agent context whatever `vault.ignore_paths` says (vault_core.ignore),
and a receive pass never commits it. Keep packages plain text with no [[wikilinks]]
(they would dangle on the other side), and never copy one back into Areas/ or
Knowledge/ — the durable facts already live in their home notes.
