Agent .md files with invalid YAML frontmatter are silently skipped without warning

Description

When a custom agent markdown file (for example .opencode/agents/test.md or ~/.config/opencode/agents/test.md) contains invalid YAML frontmatter — such as an indentation error — the file is silently skipped. The user sees no warning, no error, and no indication that the agent failed to load.

This is inconsistent with skill loading, which logs an error and publishes a Session.Event.Error when a skill file fails to parse.

Reproduction steps

1. Create .opencode/agents/test.md with malformed frontmatter indentation:

   ---
    name: test
     description: test agent
   ---
   
   You are a helpful assistant.
   

2. Start OpenCode or run opencode agent list.

3. Observe that test does not appear, and no warning or error is shown.

Root cause

In packages/opencode/src/config/agent.ts, the parse result is swallowed:

const md = await ConfigMarkdown.parse(item).catch(() => undefined)
if (!md) continue

Any FrontmatterError thrown by ConfigMarkdown.parse() is discarded, and the agent is simply omitted.

Expected behavior

At minimum, a warning should be logged so the user knows:

• which file failed
• why it failed
• that the agent was skipped

Ideally, this should behave similarly to skill parse failures: log the error with context and, when possible, surface it to the user.

Related

• #24181 (closed as stale) — described a related problem where invalid YAML caused the agent to load with degraded config.

Environment

• OpenCode version: current dev branch
• Bun 1.3+