Codex agents stop returning replies in Buzz 0.5.23 on macOS while standalone Codex works

**Describe the bug**

Codex-backed agents in Buzz stop returning replies to direct messages. The agent can appear running/active, but no response is delivered to the Buzz conversation.

This originally occurred with an existing agent, but I was able to reproduce it with:
- A duplicate of the existing agent
- A brand-new empty Codex agent using harness defaults
- A separate previously working default agent

Standalone Codex on the same Mac responds normally, which appears to isolate the failure to the Buzz/ACP agent path rather than Codex itself.

**Steps to reproduce**

1. Start a Codex-backed agent in Buzz.
2. Send a simple direct message such as: `Reply only with: TEST`
3. The agent shows activity/running state but no reply appears.
4. Stop and restart the agent.
5. Send the same simple message again.
6. No reply is returned.
7. Create a brand-new agent with no custom instructions, using Codex and harness defaults.
8. Send `Reply only with: TEST`.
9. The new agent also fails to return a reply.

As a control, I opened the standalone Codex desktop app on the same Mac and sent a simple runtime-only prompt. Codex immediately returned the expected response.

**Expected behavior**

A running Codex-backed Buzz agent should return its response to the Buzz conversation after processing the message.

**Version and platform**

- Buzz version: 0.5.23 (0.5.23)
- OS: macOS
- Architecture: Apple silicon
- Default harness: Codex
- Default model: gpt-6-astra[low]
- An agent configured with gpt-6-astra was also affected
- No custom environment variables are configured in Agent defaults

**Additional troubleshooting / observations**

- Multiple agents were stopped and restarted without resolving the issue.
- Buzz was fully quit and reopened; the problem persisted.
- A completely new empty Codex agent reproduced the problem.
- A previously working agent subsequently reproduced the same problem.
- Standalone Codex works normally on the same Mac.
- No Buzz or Codex crash reports or spin reports were found in macOS Console.
- During one controlled failed Buzz agent turn, macOS Console logged a TCC/Apple Events message indicating that `xyz.block.buzz.app` was missing the `com.apple.security.automation.apple-events` entitlement while an interaction involving Codex Computer Use was being requested. I do not know whether this is causal.
- Repeating `EXC_GUARD AST` messages associated with `buzz-desktop` were also observed, including while no controlled agent test was running, so I am not assuming those messages are related to the failure.

I have not changed macOS permissions, widened agent permissions, reinstalled Buzz, or modified the Codex installation while troubleshooting.