diff --git a/packages/agent-core-v2/src/agent/tools/agent/agentTool.ts b/packages/agent-core-v2/src/agent/tools/agent/agentTool.ts
index d294993c70..189980f557 100644
--- a/packages/agent-core-v2/src/agent/tools/agent/agentTool.ts
+++ b/packages/agent-core-v2/src/agent/tools/agent/agentTool.ts
@@ -344,15 +344,6 @@ export class SubagentTool implements ISubagentTool {
       });
     }
 
-    const runInBackground = args.run_in_background === true;
-    emitAgentRunSpawned(requester, agentId, {
-      profileName,
-      parentToolCallId: toolCallId,
-      description: args.description,
-      runInBackground,
-      model: displayModel,
-    });
-
     const target = this.lifecycle.findAgentHandle(agentId);
     if (target === undefined) throw new Error(`Agent "${agentId}" does not exist`);
     const run = await this.subagents.run(
diff --git a/packages/agent-core-v2/test/tool/tool.test.ts b/packages/agent-core-v2/test/tool/tool.test.ts
index 9ba5d047bc..babb257794 100644
--- a/packages/agent-core-v2/test/tool/tool.test.ts
+++ b/packages/agent-core-v2/test/tool/tool.test.ts
@@ -1335,6 +1335,29 @@ describe('Agent tool execution contract', () => {
     expect(result.output).toContain('child result');
   });
 
+  it('emits subagent.spawned exactly once, after task registration, carrying the task id', async () => {
+    const lifecycle = createAgentLifecycleStub({
+      createAgentIds: ['agent-child'],
+      runCompletion: async () => ({ summary: 'child result' }),
+    });
+    const context = createAgentToolContext(lifecycle);
+
+    await executeAgentTool(context, {
+      prompt: 'Investigate',
+      description: 'Find cause',
+      subagent_type: 'explore',
+    });
+
+    const spawned = lifecycle.publishedEvents.filter(
+      (event) => event.type === 'subagent.spawned',
+    );
+    expect(spawned).toHaveLength(1);
+    expect(spawned[0]).toMatchObject({
+      subagentId: 'agent-child',
+      taskId: expect.any(String),
+    });
+  });
+
   it('spawns the subagent on the pool default model when the tool call omits model', async () => {
     const lifecycle = createAgentLifecycleStub({ createAgentIds: ['agent-child'] });
     const context = createAgentToolContext(lifecycle, secondaryModelFlags(), {