quoted

The `read_refs_snapshot` uses the `parse_oid_hex` function which 
internally uses global variables. Let's instead use

Nit: s/variables/variable

No, that's fine.
It's plural, so ends with 's'.
Unless it should be "uses a global variable"

quoted

Also, while here, fix a missing newline after the functions definition.

Nit: s/functions/function

Maybe.
But it could be "the function's definition" as it could be seen as possessive.

Regards,
Richard.