fix(federation): auto-create and hydrate user profiles during DM relay

Federated 1-on-1 DMs showed the raw snowflake ID as the display name
and no avatar when the remote user had no pre-existing local record.
processCreateEvent used resolveLocalUser (find-only) instead of
resolveOrCreateReplicatedUser, and relay events carried no profile data
for participants.

- Add profile snapshot (displayName, avatar, avatarColor) to
  FederationRelayParticipant and populate it in getDmParticipants
- Change processCreateEvent to auto-create replicated user stubs and
  hydrate them with profile data from the relay event
- Fix hydrateReplicatedUserProfile URL resolution for homeInstance
  values without protocol prefix
- Fix WelcomeHeader: return null while DM data is loading (eliminates
  "unknown" flash on reload), use displayName for @mention text

packages/server/src/routes/federation.ts

@@ -1119,17 +1119,21 @@ function processCreateEvent(
     return;
   }
 
-  // Resolve ALL participants to local users
+  // Resolve ALL participants to local users, auto-creating replicated stubs
+  // for remote users that don't have a local record yet. This ensures 1-on-1
+  // federated DMs work even when the remote user hasn't connected or friended.
   const resolvedParticipants: Array<{
     localUser: typeof schema.users.$inferSelect;
     homeUserId: string;
   }> = [];
 
   for (const p of event.participants) {
-    const localUser = resolveLocalUser(p.homeUserId, db);
-    if (localUser) {
-      resolvedParticipants.push({ localUser, homeUserId: p.homeUserId });
+    let localUser = resolveOrCreateReplicatedUser(p.homeUserId, p.homeInstance, db);
+    // Hydrate with profile data from the relay event (displayName, avatar, etc.)
+    if (p.profile) {
+      localUser = hydrateReplicatedUserProfile(localUser, p.profile, db);
     }
+    resolvedParticipants.push({ localUser, homeUserId: p.homeUserId });
   }
 
   if (resolvedParticipants.length < 2) {
@@ -1875,10 +1879,11 @@ function hydrateReplicatedUserProfile(
   // Resolve bare filenames to absolute URLs pointing to the home instance.
   // The home WS doesn't run normalizeUserAssets on replicated users' avatars,
   // so they must be stored as absolute URLs to render correctly.
+  const baseUrl = user.homeInstance!.startsWith('http') ? user.homeInstance! : `https://${user.homeInstance}`;
   const resolveUrl = (filename: string | null | undefined): string | null => {
     if (!filename) return null;
     if (filename.startsWith('http')) return filename;
-    return `${user.homeInstance}/api/uploads/${filename}`;
+    return `${baseUrl}/api/uploads/${filename}`;
   };
 
   const updates: Record<string, string | null> = {};

packages/server/src/utils/federationOutbox.ts

@@ -245,6 +245,9 @@ export function getDmParticipants(dmChannelId: string): FederationRelayParticipa
       homeUserId: schema.users.homeUserId,
       homeInstance: schema.users.homeInstance,
       id: schema.users.id,
+      displayName: schema.users.displayName,
+      avatar: schema.users.avatar,
+      avatarColor: schema.users.avatarColor,
     })
     .from(schema.dmMembers)
     .innerJoin(schema.users, eq(schema.dmMembers.userId, schema.users.id))
@@ -256,6 +259,11 @@ export function getDmParticipants(dmChannelId: string): FederationRelayParticipa
   return members.map(m => ({
     homeUserId: m.homeUserId || m.id,
     homeInstance: m.homeInstance || domainOrigin,
+    profile: {
+      displayName: m.displayName ?? null,
+      avatar: m.avatar ?? null,
+      avatarColor: m.avatarColor ?? null,
+    },
   }));
 }
 

packages/shared/src/types.ts

@@ -734,6 +734,7 @@ export interface AdminResetPasswordResponse {
 export interface FederationRelayParticipant {
   homeUserId: string;
   homeInstance: string;
+  profile?: FederationRelayProfileSnapshot;
 }
 
 export interface FederationRelayEvent {

packages/web/src/components/chat/MessageList.tsx

@@ -373,10 +373,11 @@ function WelcomeHeader({ channelId }: { channelId: string }) {
 
   if (isDm) {
     const dm = dmChannels.find(d => d.id === channelId);
-    const otherUser = dm?.members.find(m => !isSelf(m, authUser));
-    const { baseName } = parseFederatedUsername(otherUser?.username ?? 'unknown');
-    const displayName = otherUser?.displayName ?? baseName;
-    const username = baseName;
+    if (!dm) return null; // DM data not yet loaded (WebSocket ready pending)
+    const otherUser = dm.members.find(m => !isSelf(m, authUser));
+    const { baseName } = parseFederatedUsername(otherUser?.username ?? '');
+    const displayName = otherUser?.displayName ?? (baseName || 'Direct Message');
+    const mentionName = otherUser?.displayName ?? baseName;
     const isFriend = otherUser ? friends.some(f => f.id === otherUser.id) : false;
 
     return (
@@ -386,7 +387,7 @@ function WelcomeHeader({ channelId }: { channelId: string }) {
         </div>
         <h3 className="text-[32px] leading-10 font-bold text-txt-primary">{displayName}</h3>
         <p className="text-txt-secondary text-[14px] mt-1">
-          This is the beginning of your direct message history with <strong>@{username}</strong>.
+          This is the beginning of your direct message history with <strong>@{mentionName}</strong>.
         </p>
         {otherUser?.homeInstance && (
           <p className="text-xs text-txt-tertiary mt-1">