fix(iios): thread subject on create, graceful open_thread error, isolated test DB

- openThread/createThread accept a generic `subject` (group name) — stored on the
  thread, echoed via listThreads; kernel never interprets it.
- Gateway open_thread now returns an ACK'd { error } on failure instead of throwing
  (which never acked → clients hung on "loading"). Non-member/missing-thread opens
  fail cleanly.
- Tests run against an isolated `iios_test` database (vitest globalSetup creates +
  migrates it; test.env overrides DATABASE_URL) so `pnpm test` can never TRUNCATE the
  dev database again. Verified: full suite green, dev DB row counts unchanged.

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

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

@@ -59,17 +59,18 @@ export class MessageService {
    * for a group. Opening an existing thread is a GOVERNED join: only an existing member may
    * re-open it (policy `iios.thread.join`) — new members enter via addParticipant.
    */
-  async openThread(threadId: string | null, principal: MessagePrincipal, opts?: { membership?: string; creatorRole?: string }): Promise<OpenThreadResult> {
+  async openThread(threadId: string | null, principal: MessagePrincipal, opts?: { membership?: string; creatorRole?: string; subject?: string }): Promise<OpenThreadResult> {
     if (!threadId) {
       await decideOrThrow(this.ports, { action: 'iios.thread.create', scope: principal });
       const scope = await this.actors.resolveScope(principal);
       const actor = await this.actors.resolveActor(scope.id, principal);
-      // `membership` + `creatorRole` are generic, app-supplied thread attributes — the kernel
-      // stores/echoes them but never branches on their chat meaning (that lives in policy + app).
+      // `membership`/`creatorRole`/`subject` are generic, app-supplied thread attributes — the
+      // kernel stores/echoes them but never branches on their chat meaning (that lives in policy + app).
       const thread = await this.prisma.iiosThread.create({
         data: {
           scopeId: scope.id,
           createdByActorId: actor.id,
+          subject: opts?.subject?.trim() || undefined,
           metadata: opts?.membership ? ({ membership: opts.membership } as Prisma.InputJsonValue) : undefined,
         },
       });