[BUG]: Custom Agents return Error or Unknown agent type on Windows Desktop App #31025

Intro

Just to be clear,
I'm not a programmer, so I used Gemini to help me create the ISSUE:

Description

Custom agents defined in Markdown files are not being recognized or loaded by the system, despite following the official documentation and having a valid configuration. While built-in agents (e.g., @general) work perfectly, any custom agent invoked via @mention or the Task tool results in a generic Error or an Unknown agent type message.

Environment

• OS: Windows 11
• App Version: OpenCode Desktop v1.16.2
• Configuration: Agents stored in C:\Users<User>.config\opencode\agents\

Expected Behavior

The agent should be loaded, and the LLM should respond based on the custom system prompt defined in the .md file.

Actual Behavior

• The system returns a generic Error (via Task tool).
• Or it returns: Unknown agent type: designer is not a valid agent type.

Troubleshooting already performed

• Verified built-in agents: @general works perfectly, confirming that the LLM connection and the Task tool infrastructure are operational.
• Frontmatter Audit: Tested different combinations of mode (primary vs subagent), added required description fields, and tried multiple model IDs.
• Path Testing: Tried both absolute paths in opencode.jsonc and relative paths.
• File System: Recreated the agents directory and files to rule out file locks or encoding issues (UTF-8).
• App Restart: Fully closed and restarted the Desktop application.

Conclusion

Since built-in agents function normally but custom .md agents fail, there seems to be a regression or a bug in the agent loading mechanism specific to the Windows Desktop implementation.

Plugins

No response

OpenCode version

OpenCode Desktop v1.16.2

Steps to reproduce

1. Create a custom agent file (e.g., designer.md) in the global agents directory with valid YAML frontmatter:

(Start of YAML block)

description: UI/UX Designer
mode: subagent
model:

System prompt content...
(End of YAML block)

2. (Optional) Explicitly add the agent to opencode.jsonc:

(Start of JSON block)
"agents": {
"DESIGNER": "C:\Users\\.config\opencode\agents\designer.md"
}
(End of JSON block)

3. Try to invoke the agent in the chat using @designer.

Operating System

Windows 11