Test Codex cloud subagent isolation

Exercise the cloud task completion signal and document why child notifications must be filtered before ACP log persistence.

Generated-By: PostHog Code
Task-Id: 971044c5-e622-4f07-b1b5-dca9b06d040c

Author: richardsolomou

packages/agent/README.md

@@ -126,6 +126,8 @@ start()
 
 The two tapping layers are distinct. The inner tap (from `createAcpConnection`) persists to logs. The outer tap (in `AgentServer`) broadcasts to SSE. This means log persistence works for both cloud and local, while SSE broadcast is cloud-only.
 
+Adapters must remove provider notifications that do not belong to the active parent session before writing ACP updates. Persisted ACP updates do not retain enough provider-specific identity to separate a subagent transcript or completion from its parent safely during cloud replay.
+
 ### HTTP endpoints
 
 | Method | Path       | Auth | Description                                              |

packages/agent/src/adapters/codex-app-server/codex-app-server-agent.test.ts

@@ -148,7 +148,10 @@ describe("CodexAppServerAgent", () => {
     });
 
     await agent.initialize(init);
-    await agent.newSession({ cwd: "/repo" } as unknown as NewSessionRequest);
+    await agent.newSession({
+      cwd: "/repo",
+      _meta: { environment: "cloud", taskRunId: "run_1" },
+    } as unknown as NewSessionRequest);
     const promptDone = agent.prompt({
       sessionId: "thr_1",
       prompt: [{ type: "text", text: "delegate this" }],
@@ -227,6 +230,12 @@ describe("CodexAppServerAgent", () => {
     const serializedUpdates = JSON.stringify(sessionUpdates);
     expect(serializedUpdates).toContain("spawn_agent");
     expect(serializedUpdates).toContain("parent response");
+    expect(serializedUpdates).not.toContain("subagent prose");
+    expect(
+      extNotifications.filter(
+        (notification) => notification.method === "_posthog/turn_complete",
+      ),
+    ).toHaveLength(1);
   });
 
   it("includes buffered command output when completion omits aggregatedOutput", async () => {