bug: Auto-Compact fails consistently, manual compact works

[NilsGoldbach]

Component

CLI

Summary

Compacting conversation history fails with the following error: Unexpected role "user" after role "tool".

Reproduction steps

This happens consistently during automatic compaction while the model is still generating. Manual compaction does not reproduce the issue. The prompt or environment seem to make no difference, it happens on every attempt.

Versions / environment

mistral-vibe 2.19.1, same issue on various OS

Logs & screenshots

Error: API error from vllm (model: cyankiwi/Devstral-Small-2-24B-Instruct-2512-AWQ-4bit): LLM backend error [vllm]
  status: 400 Bad Request
  reason: Bad Request
  request_id: N/A
  model: cyankiwi/Devstral-Small-2-24B-Instruct-2512-AWQ-4bit
  provider_message: Unexpected role 'user' after role 'tool' Unexpected role 'user' after role 'tool'
  body_excerpt: {"error":{"message":"Unexpected role 'user' after role 'tool' Unexpected role 'user' after role 'tool'","type":"BadRequestError","param":null,"code":400}}
  payload_summary: {"model":"cyankiwi/Devstral-Small-2-24B-Instruct-2512-AWQ-4bit","message_count":21,"approx_chars":34960,"temperature":0.2,"has_tools":true,"tool_choice":"auto"}

[juliendenize]

Hi thanks for the feedback. I updated the chat templates of our relatively recent models to better reflect agentic usage.

Could you try to use the novel chat template of devstral small 2
https://huggingface.co/mistralai/Devstral-Small-2-24B-Instruct-2512/blob/main/chat_template.jinja