Adapter bootstrap fails with ConnectionRefusedError on WSL2 VirtioProxy or hostAddressLoopback

Start in debugpy/adapter/main.py at the adapter's sock.connect((localhost, args.for_server)) call, then reproduce with the provided uv run command under WSL2. Compare behavior with networkingMode=VirtioProxy and hostAddressLoopback=true enabled or disabled; done means debugpy.listen() starts without ConnectionRefusedError under the affected settings.

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Environment data

• debugpy version: 1.8.21
• OS and version: Windows 11 build 26200.9106, Ubuntu 24.04 on WSL2
• Python version (& distribution if applicable, e.g. Anaconda): CPython 3.14.4, installed/managed by uv
• WSL version: 2.7.12.0
• Using VS Code or Visual Studio: bash only

Actual behavior

debugpy.listen() consistently fails during its internal adapter bootstrap. The adapter immediately fails when connecting back to debugpy's temporary callback listener:

ConnectionRefusedError: [Errno 111] Connection refused

The relevant adapter log lines are:

Sending endpoints info to debug server at localhost:<port>
ConnectionRefusedError: [Errno 111] Connection refused

This occurs before the debuggee starts and without an IDE or debugger client involved.

It occurs deterministically when either networkingMode=VirtioProxy or hostAddressLoopback=true is enabled in %UserProfile%\.wslconfig. Both settings independently trigger the problem.

Adding a time.sleep(0.2) immediately before the following line in debugpy/adapter/__main__.py works around the issue:

sock.connect((localhost, args.for_server))

Expected behavior

debugpy.listen() should start normally under WSL2 with networkingMode=VirtioProxy and/or hostAddressLoopback=true enabled.

Steps to reproduce:

1. In %UserProfile%\.wslconfig, enable either setting:

   [wsl2]
   networkingMode=VirtioProxy
   

   or:

   [experimental]
   hostAddressLoopback=true
   

2. Apply the configuration from Windows PowerShell:

   wsl --shutdown
   

3. Open WSL and run:

   uv run python -Xfrozen_modules=off -m debugpy \
     --listen 127.0.0.1:5678 \
     -c "import time; time.sleep(60)"
   

4. Observe the immediate ConnectionRefusedError from the debugpy adapter.

5. Disable the relevant .wslconfig setting, run wsl --shutdown, and repeat. The command succeeds.