Windows native crash when launching parallel subagents with local BYOK provider

[keylimesoda]

Summary

GitHub Copilot CLI crashed natively on Windows while using a BYOK/local OpenAI-compatible provider and launching multiple general-purpose subagents in parallel.

This was not a handled tool error; Windows Error Reporting recorded a native BEX64 crash in copilot.exe.

Environment

• Copilot CLI version: 1.0.45
• Platform: Windows (win32, x64)
• OS version from CLI log: 10.0.26200
• Node version from CLI log: v24.15.0
• Provider mode: custom/BYOK OpenAI-compatible provider
• Local provider: llama.cpp server at http://localhost:8080/v1
• Model: Qwen_Qwen3.6-35B-A3B-Q4_K_M.gguf
• Wire API: completions
• Prompt/context token limit configured: 120000
• Working directory at the time: a non-git parent directory (D:\Test\repos)

Windows Error Reporting details

From Windows Application event log:

Faulting application name: copilot.exe, version: 1.0.45.0
Faulting module name: copilot.exe, version: 1.0.45.0
Exception code: 0xc0000409
Fault offset: 0x00000000021f2189
Faulting process id: 0x981C
Event Name: BEX64
Report Id: 22008bd5-251d-4655-be0b-bf50b162f35e

Crash-adjacent Copilot log excerpt

The Copilot process log for PID 38940 ended immediately after dispatching three parallel general-purpose subagents:

2026-05-12T00:38:56.756Z [DEBUG] Tool calls count: 3
2026-05-12T00:38:56.757Z [DEBUG] Running tool calls in parallel
2026-05-12T00:38:56.757Z [INFO] Task tool invoked with agent_type: general-purpose, name: Shader creation, description: Create D3D12 Pong shaders
2026-05-12T00:38:56.757Z [DEBUG] Task tool dispatch: agent_type="general-purpose", inputModel="(none)", resolvedModel="(none)", implicitModel="(none)", effectiveModel="(none, will use agent default)", sessionModel="Qwen_Qwen3.6-35B-A3B-Q4_K_M.gguf"
2026-05-12T00:38:56.759Z [INFO] Task tool invoked with agent_type: general-purpose, name: Engine core creation, description: Create D3D12 Pong engine core
2026-05-12T00:38:56.759Z [DEBUG] Task tool dispatch: agent_type="general-purpose", inputModel="(none)", resolvedModel="(none)", implicitModel="(none)", effectiveModel="(none, will use agent default)", sessionModel="Qwen_Qwen3.6-35B-A3B-Q4_K_M.gguf"
2026-05-12T00:38:56.759Z [INFO] Task tool invoked with agent_type: general-purpose, name: Pong game logic, description: Create Pong game logic
2026-05-12T00:38:56.759Z [DEBUG] Task tool dispatch: agent_type="general-purpose", inputModel="(none)", resolvedModel="(none)", implicitModel="(none)", effectiveModel="(none, will use agent default)", sessionModel="Qwen_Qwen3.6-35B-A3B-Q4_K_M.gguf"
2026-05-12T00:38:56.763Z [DEBUG] General-purpose agent: agentModelSetting="capi:Qwen_Qwen3.6-35B-A3B-Q4_K_M.gguf", currentModel="Qwen_Qwen3.6-35B-A3B-Q4_K_M.gguf", modelOverride="(none)", resolvedModel="Qwen_Qwen3.6-35B-A3B-Q4_K_M.gguf"
2026-05-12T00:38:56.764Z [INFO] General-purpose agent invoked with prompt: Create the D3D12 Neon Pong HLSL shader file at `D:\Test\repos\PongGame\shaders\Pong.hlsl`.
2026-05-12T00:38:56.764Z [DEBUG] General-purpose agent: agentModelSetting="capi:Qwen_Qwen3.6-35B-A3B-Q4_K_M.gguf", currentModel="Qwen_Qwen3.6-35B-A3B-Q4_K_M.gguf", modelOverride="(none)", resolvedModel="Qwen_Qwen3.6-35B-A3B-Q4_K_M.gguf"
2026-05-12T00:38:56.764Z [INFO] General-purpose agent invoked with prompt: Create a complete D3D12 engine core for a Neon Pong game at `D:\Test\repos\PongGame\src\`.
2026-05-12T00:38:56.764Z [DEBUG] General-purpose agent: agentModelSetting="capi:Qwen_Qwen3.6-35B-A3B-Q4_K_M.gguf", currentModel="Qwen_Qwen3.6-35B-A3B-Q4_K_M.gguf", modelOverride="(none)", resolvedModel="Qwen_Qwen3.6-35B-A3B-Q4_K_M.gguf"
2026-05-12T00:38:56.764Z [INFO] General-purpose agent invoked with prompt: Create the complete Pong game logic files at `D:\Test\repos\PongGame\src\`.
2026-05-12T00:38:56.839Z [ERROR] Command failed with exit code 128: git rev-parse HEAD
2026-05-12T00:38:56.839Z [INFO] --- End of group ---

No JavaScript exception or handled stack trace appeared in the process log before exit. The Windows crash event followed immediately afterward.

Notes

Before the crash, the local model had produced some malformed Windows path/tool calls in earlier turns, but this crash appears to have happened specifically during parallel subagent startup under custom-provider mode. A failed git rev-parse HEAD in a non-git directory should not crash the CLI.

I can provide the full process log privately if helpful, but I am not attaching it to this public issue because it may include prompts and local paths.