Can not start agent with local llm

**Describe the bug**
Can not start agent with local llm

**Steps to reproduce**
1. settings-agents
2. provider choose "OpenAI-compatible"
3. add env "OPENAI_COMPAT_BASE_URL" and other params
4. choose model. model list work ok
5. start agent
6. wait, failed, and no reason

**Version and platform**
Find your version at the bottom of the Settings sidebar. Write "unknown" if you can't determine it.
- Buzz version: v0.4.26
- OS: windows

Start in Settings > Agents by reproducing the failure on Windows with the OpenAI-compatible provider and the reported OPENAI_COMPAT_BASE_URL configuration. Trace the failed agent start and identify why no reason is shown; done means the local model starts successfully or the UI reports an actionable failure reason.

Written by the indexing model from the issue text.