feat(orchestrator): add subagent session tree endpoint

apps/orchestrator/src/api/agents/agents.controller.spec.ts

@@ -6,6 +6,7 @@ import { KillswitchService } from "../../killswitch/killswitch.service";
 import { AgentEventsService } from "./agent-events.service";
 import { AgentMessagesService } from "./agent-messages.service";
 import { AgentControlService } from "./agent-control.service";
+import { AgentTreeService } from "./agent-tree.service";
 import { describe, it, expect, beforeEach, afterEach, vi } from "vitest";
 
 describe("AgentsController", () => {
@@ -42,6 +43,9 @@ describe("AgentsController", () => {
     pauseAgent: ReturnType<typeof vi.fn>;
     resumeAgent: ReturnType<typeof vi.fn>;
   };
+  let treeService: {
+    getTree: ReturnType<typeof vi.fn>;
+  };
 
   beforeEach(() => {
     // Create mock services
@@ -93,6 +97,10 @@ describe("AgentsController", () => {
       resumeAgent: vi.fn().mockResolvedValue(undefined),
     };
 
+    treeService = {
+      getTree: vi.fn().mockResolvedValue([]),
+    };
+
     // Create controller with mocked services
     controller = new AgentsController(
       queueService as unknown as QueueService,
@@ -101,7 +109,8 @@ describe("AgentsController", () => {
       killswitchService as unknown as KillswitchService,
       eventsService as unknown as AgentEventsService,
       messagesService as unknown as AgentMessagesService,
-      controlService as unknown as AgentControlService
+      controlService as unknown as AgentControlService,
+      treeService as unknown as AgentTreeService
     );
   });
 
@@ -113,6 +122,27 @@ describe("AgentsController", () => {
     expect(controller).toBeDefined();
   });
 
+  describe("getAgentTree", () => {
+    it("should return tree entries", async () => {
+      const entries = [
+        {
+          sessionId: "agent-1",
+          parentSessionId: null,
+          status: "running",
+          agentType: "worker",
+          taskSource: "internal",
+          spawnedAt: "2026-03-07T00:00:00.000Z",
+          completedAt: null,
+        },
+      ];
+
+      treeService.getTree.mockResolvedValue(entries);
+
+      await expect(controller.getAgentTree()).resolves.toEqual(entries);
+      expect(treeService.getTree).toHaveBeenCalledTimes(1);
+    });
+  });
+
   describe("listAgents", () => {
     it("should return empty array when no agents exist", () => {
       // Arrange