Harden the seams a project sweep surfaced

A systematic review of the whole codebase (main process, renderer,
IPC/migration/packaging seams) surfaced four real defects; each is
fixed at its root:

- Legacy catalogue drift: the operator's profile still carried 89
  active skills from the removed ~/.agents import era next to the 228
  built-ins. Catalogue sync now mirrors the bundle - actives whose slug
  the bundle does not ship retire (bindings keep resolving via their
  pinned revisions; retired skills leave list_skills and cannot be
  granted anew)
- Broken-bundle guard: staging now refuses a bundle without the
  humanizer skill, so an empty or quarantined resources folder can
  never trigger the mirror pass into retiring a healthy catalogue
- Duplicate agent names: @mentions, DM routing, and task assignment all
  resolve by name, so createAgent and updateAgent renames now reject a
  name already held by an active agent (case-insensitive); the mention
  resolver still refuses to guess between legacy duplicates
- Stale DM titles: agent-to-agent conversation rows titled themselves
  from the frozen creation-time space name, so renames never reached
  the sidebar; direct titles now derive from members' current names

Verified clean in the same sweep: IPC surface (82 channels, handler +
preload + api aligned), per-migration transactions with rollback,
quota-parking month rollover, retry-budget counting, meeting spot
reuse across floor-plan rebuilds.

src/main/services/organization-service.ts

@@ -76,6 +76,7 @@ export class OrganizationService {
 
   createAgent(input: CreateAgentInput): string {
     assertUsableMentionName(input.name);
+    this.assertAgentNameAvailable(input.orgId, input.name, null);
     const hiringPolicy = this.governance.enforceHiringPolicy(input);
     const id = createId("agt");
     const now = new Date().toISOString();
@@ -154,7 +155,10 @@ export class OrganizationService {
     if (!role) throw new Error("Agent role is required.");
     const name = input.name === undefined ? agent.name : input.name.trim();
     if (!name) throw new Error("Agent name is required.");
-    if (name !== agent.name) assertUsableMentionName(name);
+    if (name !== agent.name) {
+      assertUsableMentionName(name);
+      this.assertAgentNameAvailable(input.orgId, name, input.agentId);
+    }
     if (input.modelProviderId) {
       const provider = this.db.prepare("select id from providers where id = ? and org_id = ?")
         .get(input.modelProviderId, input.orgId) as { id: string } | undefined;
@@ -330,6 +334,19 @@ export class OrganizationService {
     if (goalId && project.goal_id !== goalId) throw new Error("Project is linked to a different goal.");
   }
 
+  /**
+   * Agent names are identities: @mentions, DM routing, and task assignment
+   * all resolve by name, so two active agents must never share one.
+   */
+  private assertAgentNameAvailable(orgId: string, name: string, exceptAgentId: string | null): void {
+    const clash = this.db.prepare(`
+      select id from agents
+      where org_id = ? and lifecycle = 'active' and lower(name) = lower(?) and (? is null or id <> ?)
+      limit 1
+    `).get(orgId, name.trim(), exceptAgentId, exceptAgentId) as { id: string } | undefined;
+    if (clash) throw new Error(`An active agent named "${name.trim()}" already exists. Pick a different name.`);
+  }
+
   private addAgentToWorkspaceSpaces(orgId: string, agentId: string): void {
     const spaces = this.db.prepare("select id from chat_spaces where org_id = ? and visibility = ? and space_type <> ?")
       .all(orgId, "workspace", "direct") as Array<{ id: string }>;