Cloudflare Workers AI models fail on the first message

Description

Cloudflare Workers AI models can fail on the first message in two ways. Models that report output == context trigger ContextOverflowError before a request is sent because almost the whole context is reserved for output. Models that reach Workers AI can receive HTTP 400 System message must be at the beginning when a system transform produces multiple system messages.

Plugins

Reproduces when a system transform splits the system prompt.

OpenCode version

1.18.25

Steps to reproduce

1. Authenticate cloudflare-workers-ai and set CLOUDFLARE_ACCOUNT_ID.
2. Select a Workers AI model such as @cf/qwen/qwen2.5-coder-32b-instruct or @cf/qwen/qwen3.8-27b.
3. Send the first message.

Screenshot and/or share link

N/A

Operating System

Windows 11

Terminal

Windows Terminal