fix(lexer): treat trailing CR as line end so comment text is idempotent

Assisted-by: GLM 5.3 Flash

lexer/lexer.go

@@ -186,15 +186,19 @@ func (l *Lexer) Next() token.Token {
 }
 
 // lineComment consumes a // comment up to, but not including, the newline.  A
-// trailing \r is part of a CRLF line ending rather than comment content:
-// dropping it keeps the formatter's output uniformly LF-terminated.
+// trailing run of \r, spaces and tabs is line-ending whitespace rather than
+// comment content, so it never enters the token text.  Trimming only a \r
+// directly before the token's end would make the text depend on what follows
+// the comment (a newline or the end of the input): "//x\r " would carry the
+// "\r " while "//x\r\n" would not, and a formatter that terminates the line
+// with \n would then re-lex its own output to a shorter comment.
 func (l *Lexer) lineComment(start token.Position) token.Token {
 	var b strings.Builder
 	for !l.atEnd() && l.cur() != '\n' {
 		b.WriteRune(l.cur())
 		l.advance()
 	}
-	return l.make(token.Comment, start, strings.TrimSuffix(b.String(), "\r"))
+	return l.make(token.Comment, start, strings.TrimRight(b.String(), " \t\r"))
 }
 
 // blockComment consumes a /* ... */ comment, tolerating an unterminated one.