Windows: bash tool fails (WinError 2) and web.fetch timeout can cascade to max_steps_reached

[shawbaiw]

Summary

On Windows, bub can hit two issues in one session:

1. bash tool fails with FileNotFoundError: [WinError 2] when bash is unavailable.
2. web.fetch timeout can surface as repeated tool failures, and the run may end with max_steps_reached=20.

Environment

• OS: Windows (PowerShell)
• Python: 3.14
• uv: 0.10.8
• Project: bubbuild/bub

Reproduction

1. Start CLI:

   uv run bub
   

2. Ask a prompt that includes an URL, e.g.:

   简单介绍一下你自己(https://github.com/bubbuild/bub)
   

Expected

• If web.fetch times out, return a friendly error and continue safely.
• Shell tool should still work on Windows environments without bash.

Actual

• web.fetch may raise timeout tracebacks.
• bash tool tries bash -lc ... only, then fails with WinError 2.
• Model may keep stepping and end with max_steps_reached=20.

Error snippets

web.fetch timeout:

TimeoutError
...
aiohttp.ClientSession(...)
session.get(...)

bash tool error:

FileNotFoundError: [WinError 2] 系统找不到指定的文件。

Suggested fix

• In src/bub/tools/builtin.py:
  • bash tool: choose shell by platform (bash -> pwsh/powershell on Windows -> sh).
  • web.fetch: catch asyncio.TimeoutError and return a readable timeout message.

If useful, I can open a PR with this change.

[glasscatya]

I noticed this issue too, but I thought bub didn't intend to support Windows in the first place.