hermes - 💡(How to fix) Fix PTY stdin write fails: 'bytes' object cannot be converted to 'PyString'

Description

When using terminal(pty=true, background=true) to run interactive CLI tools (e.g. opencode), the process(action="write") and process(action="submit") actions fail with:

argument to_write: bytes object cannot be converted to PyString

This blocks sending any input to PTY-based background processes.

Steps to Reproduce

1. Start a PTY process:

   terminal(command="opencode", background=true, pty=true)

2. Try writing input:

   process(action="write", session_id="proc_xxx", data="test")

3. Observe the error.

Environment

• Hermes Agent: v0.15.1 (2026.5.29)
• OS: Windows 10 (git-bash)
• Python: 3.11.15
• OpenAI SDK: 2.24.0

Notes

The error message references PyString — a Python 2 C API type that was removed in Python 3. This suggests a Python 2/3 compatibility issue in the PTY stdin writing code path. Likely a ctypes or C extension call is using the wrong type for string data on Python 3.11.

Workaround

Use non-PTY mode or tmux as an intermediary for interactive CLI sessions (as documented in the Hermes spawning guide).