The test's debug "print background log" code opened the file
in text mode with utf-8 encoding. The sloppy.py GUI process writes
Windows console output that includes cp1252-encoded bytes (e.g.,
0x97 in position 1704 in the captured failure). Opening in text
mode raises UnicodeDecodeError on the first non-utf-8 byte.
Fix: open in binary mode and decode with errors='replace' so the
print is best-effort and never crashes the test.
This is a test-only fix. Production code paths unchanged.
ed