Currently any command that uses heredoc format will hang when using exec because of the line here:

script += `  { ${command}; } > >(while IFS= read -r line || [[ -n "$line" ]]; do printf '\\x01\\x01\\x01%s\\n' "$line"; done >> "$log") 2> >(while IFS= read -r line || [[ -n "$line" ]]; do printf '\\x02\\x02\\x02%s\\n' "$line"; done >> "$log")\n`;

I think it's because bash expects the heredoc terminator to be alone on its line and we're putting the user command in a single physical line. So I think a simple fix would be to format the commands to make sure they start/end with new lines?