PR #25200: fix(cli): add windows_subprocess_kwargs() to force UTF-8 in subprocess text output

• Repository: NousResearch/hermes-agent
• Author: erhnysr
• State: open | merged: False
• Link: https://github.com/NousResearch/hermes-agent/pull/25200

Description (problem / solution / changelog)

Fixes #25191

Problem

On Windows, subprocess.run(..., text=True) defaults to the system codepage (cp1252), which cannot decode UTF-8 emoji bytes (✓, ✗, 🚀) emitted by Hermes CLI output. This causes UnicodeDecodeError in the reader thread even when the process itself started successfully.

hermes_cli/__init__.py already has _ensure_utf8() that reconfigures sys.stdout/sys.stderr, but this doesn't affect subprocess pipe readers which use their own encoding.

Fix

Adds windows_subprocess_kwargs() helper to _subprocess_compat.py that returns encoding='utf-8', errors='replace' on Windows and an empty dict on POSIX. Callers can spread this into subprocess.run() calls alongside capture_output=True, text=True.

Root cause

subprocess.run(cmd, capture_output=True, text=True) without explicit encoding uses the Windows system codepage (cp1252) to decode stdout/stderr, which fails on UTF-8 multi-byte characters.

Changed files

• gateway/run.py (modified, +6/-5)
• hermes_cli/_subprocess_compat.py (modified, +18/-0)