I apologize -- the parens problem is because it's unbalanced, but, you're right, it's more subtle than what I originally said. The parameter list for an attribute isn't really parsed normally. From attributes:

   An attribute list is a sequence of attribute specifications, separa
+ted
   by whitespace or a colon (with optional whitespace). Each attribute
   specification is a simple name, optionally followed by a parenthesi
+sed
   parameter list. If such a parameter list is present, it is scanned 
+past
   as for the rules for the "q()" operator. (See "Quote and Quote-like
   Operators" in perlop.) The parameter list is passed as it was found
+,
   however, and not as per "q()".

   Some examples of syntactically valid attribute lists:

       switch(10,foo(7,3))  :  expensive
       Ugly('\(") :Bad
       _5x5
       locked method

   Some examples of syntactically invalid attribute lists (with
   annotation):

       switch(10,foo()             # ()-string not balanced
       Ugly('(')                   # ()-string not balanced
       5x5                         # "5x5" not a valid identifier
       Y2::north                   # "Y2::north" not a simple identifi
+er
       foo + bar                   # "+" neither a colon nor whitespac
+e
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Reading between the lines, the difference in the "Ugly" specs above seems to be the use of the backslash on the "(" in the first example. You might try backspacing your inner "(" and see if that helps.

If the parens problem is fixed, you will need the use statement after the package statement because Class::Std exports subroutines that the attributes mechanism looks for in the current package when an attribute is detected. See my post, Re: Class::Std : How does MODIFY_HASH_ATTRIBUTES work? for details.