Simple question: Should I make sure to use Unix line endings for my robots.txt, or does it not matter?
It doesn't matter. According to the spec:
The file consists of one or more records separated by one or more blank lines (terminated by CR,CR/NL, or NL).
- CR = Carriage Return (i.e. \r)
- CR/NL = Carriage Return/New Line (i.e. \r\n)
- NL = New Line (i.e. \n)
This means you can use
\r\n and it will work.