it looks like @ARGV and $ARGV are stripped of all magic by the manipulation

No, they were never magical in the first place.

>perl -MDevel::Peek -e"Dump($ARGV,1);" 2>&1 | find "MAGIC"

>perl -MDevel::Peek -e"Dump(\@ARGV,1);" 2>&1 | find "MAGIC"

>perl -MDevel::Peek -e"Dump(\%ENV,1);" 2>&1 | find "MAGIC"
    MAGIC = 0x4c7ed8
      MG_TYPE = PERL_MAGIC_env(E)
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They are simply set by reading from the magical file handle ARGV, which is no longer being read from.