Summary

Fixes UnicodeDecodeError crash in Windows gateway process scanning by adding explicit encoding and error handling to the wmic subprocess.run call.

Root Cause

On Windows systems, especially with non-English locales, the wmic command outputs text in the system's code page (e.g., cp936 for Chinese, cp1252 for Western European), not UTF-8.

The current code in hermes_cli/gateway.py (lines 278-283) calls subprocess.run with text=True, which implicitly uses UTF-8 encoding. When wmic output contains non-UTF-8 bytes:

1. Python's subprocess raises UnicodeDecodeError in the reader thread
2. result.stdout becomes None after decode failure
3. Line 287 crashes with AttributeError: 'NoneType' object has no attribute 'split'

Fix

• Add explicit encoding='utf-8' to subprocess.run call
• Add errors='ignore' to skip undecodable bytes instead of crashing
• Check result.stdout is None before splitting to avoid AttributeError

This allows the setup wizard to continue gracefully on systems where wmic output cannot be fully decoded, returning an empty PID list instead of crashing.

Testing

• Added regression test TestScanGatewayPids::test_handles_wmic_unicode_decode_error_gracefully that simulates decode failure (stdout=None) and verifies empty list is returned
• Existing test test_find_gateway_pids_falls_back_to_pid_file_when_process_scan_fails still passes

Impact

• Fixes crash during hermes setup on Windows with non-English locales
• No functional regression: setup wizard continues with empty PID scan, which falls back to PID file discovery
• Small, focused change: 3 lines in gateway.py, 1 test class

Fixes #17049