A direct message answers in the form its recipient writes in

Lemmy 0.19 (most of the threadiverse) and Mbin take a private message only
as a ChatMessage and refuse a direct Note. A direct message to one account
elsewhere that writes to us as ChatMessages now goes out as one: to it
alone, without a mention in its text, kept on the post (Post.AsChatMessage)
so the served copy and an edit match. No software name decides it.

Live against Lemmy 0.19: alice's answer to lemmyuser's private message and
another persona's message to lemmyuser arrive (29 checks). A first message
to an account that never wrote to anyone here is still a Note, which they
refuse; G-0008 keeps that open for the owner.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LsXgEaXee4GCU1hwYgPJXw

FEDERATION.md

@@ -158,6 +158,10 @@ persona's posts passed on to its followers. A deleted post answers 410 with a `T
 - **Blocks are sent.** A blocked remote account receives `Block` from the blocking account (and `Reject{Follow}` if it
   followed); an unblock sends `Undo{Block}`.
 - **Reports** are sent as `Flag` by the instance actor, never by the reporting account.
+- **Direct messages** go out as a `Note` addressed to their recipients, except to someone who writes to us as
+  `ChatMessage`s (Pleroma's type, which Lemmy 0.19 and Mbin take as their only private messages): a message to that one
+  account alone goes out as a `ChatMessage`, to it alone, without a mention in its text. The first message to an
+  account that never wrote to anyone here is still a `Note`, which Lemmy 0.19 and Mbin refuse (G-0008).
 - **Replies are passed on** (inbox forwarding; owner decision 2026-10-05). A public or unlisted reply from another server
   to a persona's public, unlisted or followers-only post goes on to the persona's followers as its author's server sent
   and signed it, the way Mastodon forwards it: to every follower's server but the replier's own. Its `Update` and