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Clarify plugin guidance for experimental.chat.system.transform to avoid extra system messages #23660
Description
Description
A lot of memory/context plugins use experimental.chat.system.transform by doing output.system.push(...) for recalled context or status blocks.
That is a natural reading of the current hook type, but it can make those plugins incompatible with many model backends that only accept a single system message at the start of the conversation, especially vLLM-served Qwen models and similar OpenAI-compatible deployments.
The hook itself is useful and does not need a behavior change here. What seems to be missing is guidance for plugin authors: if they are adding supplemental prompt/context, they should usually merge it into the primary system block instead of pushing a new array entry.
Plugins
Memory and context injection plugins using experimental.chat.system.transform
OpenCode version
Current dev branch as of 2026-04-21
Steps to reproduce
- Implement a plugin that injects recalled context with
output.system.push(...)insideexperimental.chat.system.transform - Use that plugin with an OpenAI-compatible backend that only allows a single system message
- Send a request
- The backend rejects the request because multiple system messages were produced
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Operating System
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Terminal
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Activity
github-actions commentedon Apr 21, 2026
This issue might be a duplicate of existing issues. Please check:
experimental.chat.system.transformto push additional system message entries causes Qwen/vLLM-compatible backends (which only accept a single system message at the start) to reject the request with "system message must be at the beginning". The symptoms and affected backends are identical.If your issue is the same, please consider adding your context there. If it's meaningfully different (e.g. you're specifically requesting documentation/guidance for plugin authors rather than reporting a runtime error), please clarify that distinction in this issue.
zhangdw156 commentedon Apr 21, 2026
Related, but narrower: issue-20785 reports the runtime failure itself. This issue is specifically asking for plugin-author guidance on
experimental.chat.system.transformso plugin authors avoid creating extra system-message entries in the first place. No hook behavior change requested here, only clearer guidance/docs for plugin authors.github-actions commentedon Jul 3, 2026
To stay organized issues are automatically closed after 60 days of no activity. If the issue is still relevant please open a new one.