Surface cross-workspace subagents in their workspaces (#2061)

* fix(workspaces): show provider subagent activity

Provider subagent lifecycle lives outside managed agent snapshots, so workspace aggregation dropped it after the parent turn finished. Count running provider subagents against the delegation root and emit workspace updates when their status changes.

* fix(workspaces): surface cross-workspace subagents

packages/app/src/utils/workspace-agent-activity.test.ts

@@ -155,6 +155,52 @@ describe("workspace agent activity index", () => {
     });
   });
 
+  it("treats a cross-workspace subagent as activity in its own workspace", () => {
+    const index = buildWorkspaceAgentActivityIndex(
+      new Map([
+        [
+          "parent",
+          agent({
+            id: "parent",
+            workspaceId: "workspace-a",
+            updatedAt: "2026-06-01T10:00:00.000Z",
+          }),
+        ],
+        [
+          "child",
+          agent({
+            id: "child",
+            workspaceId: "workspace-b",
+            status: "running",
+            updatedAt: "2026-06-01T10:03:00.000Z",
+            parentAgentId: "parent",
+          }),
+        ],
+      ]),
+    );
+
+    expect(index).toEqual(
+      new Map([
+        [
+          "workspace-a",
+          {
+            agentId: "parent",
+            status: "done",
+            enteredAt: new Date("2026-06-01T10:00:00.000Z"),
+          },
+        ],
+        [
+          "workspace-b",
+          {
+            agentId: "child",
+            status: "running",
+            enteredAt: new Date("2026-06-01T10:03:00.000Z"),
+          },
+        ],
+      ]),
+    );
+  });
+
   it("preserves the activity index while the same agent remains in the same status", () => {
     const previous = buildWorkspaceAgentActivityIndex(
       new Map([

packages/app/src/utils/workspace-agent-activity.ts

@@ -1,4 +1,5 @@
 import type { Agent, WorkspaceDescriptor } from "@/stores/session-store";
+import { isWorkspaceRootAgent } from "@/subagents/policies";
 import { deriveSidebarStateBucket } from "./sidebar-agent-state";
 
 export interface WorkspaceAgentActivity {
@@ -15,7 +16,8 @@ export function buildWorkspaceAgentActivityIndex(
   const latestActivityAtByWorkspaceId = new Map<string, Date>();
 
   for (const agent of agents.values()) {
-    if (agent.archivedAt || agent.parentAgentId || !agent.workspaceId) {
+    const parentAgent = agent.parentAgentId ? agents.get(agent.parentAgentId) : undefined;
+    if (agent.archivedAt || !agent.workspaceId || !isWorkspaceRootAgent(agent, parentAgent)) {
       continue;
     }