Second Windows-specific sandbox bug (WinError 10106 was the first):
after the env-scrub fix let the child start, it immediately failed to
import hermes_tools with:
SyntaxError: (unicode error) 'utf-8' codec can't decode byte 0x97
in position 154: invalid start byte
Root cause: _execute_local wrote the generated hermes_tools.py stub and
the user's script.py via open(path, 'w') without encoding=. On Windows
the default text-mode encoding is cp1252 (system locale), which encodes
em-dashes (used in the stub's docstrings) as 0x97. Python then decodes
source files as UTF-8 (PEP 3120) on import, chokes on 0x97, and the
sandbox dies before any tool call.
Fix: pass encoding='utf-8' to all four file opens in the code_execution
path — the two staging writes in _execute_local (hermes_tools.py +
script.py) and the two RPC file-transport reads/writes in the generated
remote stub. JSON is ASCII-safe for most payloads but tool results
(terminal output, web_extract content) routinely carry non-ASCII.
Tests added (4):
- test_stub_and_script_writes_specify_utf8 — source grep guard
- test_file_rpc_stub_uses_utf8 — generated remote stub check
- test_stub_source_roundtrips_through_utf8 — concrete round-trip
- test_windows_default_encoding_would_have_failed — negative control
(skips on modern Python builds where default is already UTF-8
compatible, but retained for platforms where the regression could
return)
24/25 tests pass on Windows 3.11 (negative control skips because this
Python build handles em-dashes via cp1252 subset — the fix is still
correct, just the corruption path isn't always triggerable).
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