feat(iios): include participant names in listThreads (generic)

GET /v1/threads now returns participants[] (member usernames) so a host app can
render conversation titles / member lists without a second call. Still generic —
it only lists members of threads the caller belongs to.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/iios-service/src/messaging/message.service.ts

@@ -24,6 +24,7 @@ export interface ThreadSummary {
   threadId: string;
   subject: string | null;
   membership?: string;
+  participants: string[];
   participantCount: number;
   unread: number;
   lastMessage?: string;
@@ -135,11 +136,20 @@ export class MessageService {
     const threadIds = memberships.map((m) => m.threadId);
     if (threadIds.length === 0) return [];
 
-    const [threads, unreads] = await Promise.all([
+    const [threads, unreads, allParts] = await Promise.all([
-      this.prisma.iiosThread.findMany({ where: { id: { in: threadIds } }, include: { _count: { select: { participants: true } } } }),
+      this.prisma.iiosThread.findMany({ where: { id: { in: threadIds } } }),
       this.prisma.iiosUnreadCounter.findMany({ where: { threadId: { in: threadIds }, actorId: actor.id } }),
+      this.prisma.iiosThreadParticipant.findMany({
+        where: { threadId: { in: threadIds } },
+        include: { actor: { include: { sourceHandle: true } } },
+      }),
     ]);
     const unreadBy = new Map(unreads.map((u) => [u.threadId, u.unreadCount]));
+    const membersBy = new Map<string, string[]>();
+    for (const p of allParts) {
+      const name = p.actor?.sourceHandle?.externalId ?? p.actor?.displayName ?? p.actorId;
+      membersBy.set(p.threadId, [...(membersBy.get(p.threadId) ?? []), name]);
+    }
 
     const summaries = await Promise.all(
       threads.map(async (t) => {
@@ -148,11 +158,13 @@ export class MessageService {
           orderBy: { occurredAt: 'desc' },
           include: { parts: { where: { kind: 'TEXT' }, take: 1 } },
         });
+        const members = membersBy.get(t.id) ?? [];
         return {
           threadId: t.id,
           subject: t.subject,
           membership: (t.metadata as { membership?: string } | null)?.membership,
-          participantCount: t._count.participants,
+          participants: members,
+          participantCount: members.length,
           unread: unreadBy.get(t.id) ?? 0,
           lastMessage: last?.parts[0]?.bodyText ?? undefined,
           lastAt: last?.occurredAt,