parse-feat's paren-open handler stripped the grouping parens and
returned the inner feature, leaving any trailing ident (like `em`)
as a separate top-level feature. After consuming the closing paren,
now checks if the next token is a non-keyword ident or `%` op and
wraps as (string-postfix inner unit), making `(0 + 1) em` → "1em".
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
giles
fee62a20f0