Bug: Unknown agent frontmatter fields leak into LLM API request body via options #12964

Description

Unknown YAML frontmatter fields in custom agent .md files (e.g. tts, permissions, voice, tags, metadata) are silently collected into agent.options by the .catchall(z.any()).transform() in config.ts. These then get merged into the LLM API request body via mergeDeep(input.agent.options) in llm.ts:111.

Strict API providers (OpenAI, Vertex AI, OpenRouter/Zen) reject the request with errors like Extra inputs are not permitted, causing agents to silently return empty responses.

Root Cause

In packages/opencode/src/config/config.ts (~line 728-732):

const options: Record<string, unknown> = { ...agent.options }
for (const [key, value] of Object.entries(agent)) {
  if (!knownKeys.has(key)) options[key] = value  // ← unknown fields go into options
}

Then in llm.ts:111, mergeDeep(input.agent.options) sends them to the API.

Steps to Reproduce

1. Create a custom agent .md file with any non-standard frontmatter field:

   ---
   name: my-agent
   model: openai/gpt-4o
   tts: true
   custom_field: "hello"
   ---

2. Spawn this agent via Task tool
3. The API request body will contain tts: true and custom_field: "hello"
4. Strict providers reject the request; the agent returns empty/broken output

Expected Behavior

Only fields explicitly declared under options: in frontmatter should be sent to the LLM API. Unknown fields should be preserved on the agent object (for hooks/plugins) but not merged into API requests.

Related Issues

• Vertex AI: BadRequestError 'instructions: Extra inputs are not permitted' when running agents #4282 — Vertex AI Extra inputs are not permitted (same root cause)
• .opencode/agents/ folder agents are giving the <tool_call> response #12950 — Agents giving raw <tool_call> responses (likely same root cause)

Environment

• OpenCode: dev branch (commit 83853cc)
• Providers affected: Any strict API (OpenAI, Vertex AI, OpenRouter, Zen)