Invalid YAML in agent .md frontmatter silently ignored — agent loads with degraded config #24181

Description

Description

When an agent .md file contains invalid YAML frontmatter, OpenCode loads the
agent anyway — but all frontmatter is silently discarded. The agent loads
with its filename-derived name and without its prompt, permissions, or tool
configuration. No error is shown to the user.

## Root cause

gray-matter (the YAML frontmatter parser) does not throw on invalid
YAML by default. When js-yaml fails (e.g., skill:true without space),
gray-matter returns the raw frontmatter as a string in md.data instead
of a parsed object.
This means:

• ConfigMarkdown.parse() never throws → the catch block in loadAgent
  is never reached → no Session.Event.Error is published
• { ...md.data } spreads a string → garbage instead of config
• The explicit name: agentName (from filename) survives, masking the error

Relevant code

packages/opencode/src/config/markdown.ts:71-89

export async function parse(filePath: string) {
    const template = await Filesystem.readText(filePath)
    try {
        const md = matter(template)
        return md   // ← returns with md.data as string on YAML error
    } catch { ... }
}

packages/opencode/src/config/config.ts:219-231

const config = {
    name: agentName,        // ← "my-agent" from filename
    ...md.data,             // ← string spread → garbage, loses frontmatter name
    prompt: md.content.trim(),
}
const parsed = Agent.safeParse(config)
if (parsed.success) {
    result[config.name] = parsed.data   // ← key is still the filename-based name
}

Suggested fix

Validate that md.data is actually parsed structured data, not a raw string
fallback:

const md = matter(template)
if (typeof md.data === "string") {
    // gray-matter returned raw string: YAML parse failed
    throw new FrontmatterError(...)
}

Or pass { language: "yaml", strict: true } to matter() so it throws on
invalid YAML instead of silently returning a raw string.

Plugins

none

OpenCode version

1.14.23

Steps to reproduce

1. Create .opencode/agents/my-agent.md:

   ---
   name: myAgent
   mode: primary
   permission:
     "*": deny
     read: allow
     grep: allow
     skill:true       # ← missing space after colon
   ---
   You are an expert...

2. Start opencode server
3. Run opencode agent list or open the TUI agent picker
4. Agent appears as my-agent (filename-based) instead of myAgent
5. The prompt and permissions from the frontmatter are not applied

Screenshot and/or share link

No response

Operating System

Windows 11

Terminal

windows terminal