opencode-empty-content-fix

opencode plugin that prevents [System: Empty message content sanitised to satisfy protocol] from appearing in conversations when using an OpenAI-compatible gateway (LiteLLM, Open WebUI, token-plan gateways, ...).

Why it happens

When an assistant turn contains only tool calls, the AI SDK serializes it with content: "" on the wire. OpenAI-compatible gateways sanitize empty content by replacing it with the placeholder text above, then echo it back into the conversation history. opencode's own empty-content filter only covers @ai-sdk/anthropic and @ai-sdk/amazon-bedrock, so proxy-routed providers are affected.

What this plugin does

• experimental.chat.messages.transform — before every request:
  • strips placeholder text parts from the outgoing history, and
  • injects a non-empty text part into assistant turns that carry tool calls but no text, so the wire content is never empty and the gateway has nothing to sanitize.
  • reasoning parts are never touched (they may carry positionally sensitive provider signatures).
• experimental.chat.system.transform — drops empty/whitespace-only system prompt entries.

Already-polluted history stays in the database and is still rendered by the UI; the plugin stops new placeholders from being generated. Start a new session for a clean transcript.

Usage

Enable the plugin in your opencode config (~/.config/opencode/opencode.jsonc for global):

{
  "plugin": [
    "@omsfuk/opencode-empty-content-fix"
  ]
}

opencode installs npm plugins on demand. You can also use a local path or file:// URL for development. Restart opencode after changing the config.

Development

bun install
bun run typecheck
bun test