Claude Code Authentication Issue

**Describe the bug**
I'm getting the following error when I try to use an agent powered by Claude Code:

⚠️ I couldn't process the last request: authentication failed. Please re-authenticate the CLI (e.g. run claude /login or codex login) and then re-send.

I tried sign out and in again in the Claude Desktop and restarting both Claude and Buzz but no success.

**Steps to reproduce**
1. Trigger Agent that's using Claude harness
2. System will throw some errors on agent view
3. Agent will report the error back

**Expected behavior**
It was working until a couple of days ago.

**Version and platform**

- Buzz version: 0.5.11
- OS: MacOS 26.5.2

Start by reproducing the failure from an agent using the Claude harness on Buzz 0.5.11 on macOS, following the listed authentication error and re-authentication steps. Trace the authentication path used when the agent is triggered; done means the agent processes the request successfully after authentication without reporting an error.

Written by the indexing model from the issue text.