Once a cross-server DM exists, the thread, participant identities, and message homing must render correctly with qualified IDs.

What to do

• Render the DM participant (remote user) with their home-domain identity/avatar.
• Ensure message send/receive, edit/delete, reactions, and typing all work in a replica DM channel (qualified channel ID).
• Handle the replica-vs-home distinction transparently for the user.

Acceptance

• A cross-server DM behaves like a local DM from the user's perspective, with correct remote identity rendering.

Server reference

• Replica vs home DM channel model: src/federation/dm.rs (open_dm_as_home / open_dm_as_replica).

Server reference — accordserver branch claude/federated-servers-xlydlj.