Fail Tool Calls

[zzyu17]

Describe the bug

When configuring Copilot to use DeepSeek-V4 models (either Flash or Pro), 400 error occurs:

✗ 400 {"error":{"message":"messages.108: `tool_use` ids were found without `tool_result` blocks immediately after: call_8ZMDT1DJ43gofat5AalrxCTn. Each `tool_use` block must have a corresponding `tool_result` block in the next 
  message.","type":"invalid_request_error","param":null,"code":"invalid_request_error"}} 

Affected version

1.0.44

Steps to reproduce the behavior

No response

Expected behavior

No response

Additional context

• OS: WSL2 (Ubuntu 24.04)
• Config:

  export COPILOT_PROVIDER_BASE_URL="https://api.deepseek.com/anthropic"
  export COPILOT_PROVIDER_TYPE="anthropic"
  export COPILOT_MODEL="deepseek-v4-flash"/"deepseek-v4-pro"
  export COPILOT_PROVIDER_MAX_PROMPT_TOKENS="1000000"
  export COPILOT_PROVIDER_MAX_OUTPUT_TOKENS="384000"

[zzyu17]

Also, is there a feature to downgrade/reinstall specific version of Copilot CLI?
I have tried uninstall and reinstall via npm (npm install -g @github/copilot@1.0.42) and download script (curl -fsSL https://gh.io/copilot-install | VERSION="v1.0.42" bash) with specified version (1.0.42), but after reinstalling, Copilot CLI is still at 1.0.44.

[zzyu17]

I seem to find the possible cause and quick workaround:
The fail tool call can be caused by conflicting simultaneous incoming message from user (e.g., when the same session is being resumed in several terminals and prompts come in at the same time). Removing the corresponding entries in .copilot/session-state/<session-id>/events.jsonl can help.