Multiple system prompts break Qwen3.5-* models

Description

As part of investigating what could've caused https://github.com/Opencode-DCP/opencode-dynamic-context-pruning/issues/407 I noticed that the tool was adding another system prompt, which caused for this model to break.

Despite being fixed in the plugin it makes sense to at least have it as a known issue, so this is mostly for documentation purposes and if there are other plugins that could incur such behavior for the qwen3.5 or other models.

Also maybe as a suggestion if there are multiple system prompts to be concatenated into a single one before dispatch to the model, similarly to how it is done here

Plugins

@tarquinen/opencode-dcp

OpenCode version

1.2.12

Steps to reproduce

1. Install @tarquinen/opencode-dcp with version <= 2.1.7
2. Start a session with any of the Qwen3.5 models
3. Send a message and expect to receive error this error

Screenshot and/or share link

No response

Operating System

EndeavourOS

Terminal

Ghostty