StdLexical line comment swallows all text after it

[atennapel]

I have a parser in Scala 3:

object Parser extends StdTokenParsers with PackratParsers:
  type Tokens = StdLexical
  val lexical = Lexer
  lexical.delimiters ++= Seq(
    "\\",
    "λ",
    ".",
    "(",
    ")",
    "{",
    "}",
    ":",
    "=",
    ";",
    "->"
  )
  lexical.reserved ++= Seq("Type", "let", "def")

  type P[+A] = PackratParser[A]

  // more things specific to the language here

  def parseDecls(str: String): ParseResult[Decls] =
    val tokens = new lexical.Scanner(str)
    phrase(decls)(tokens)

  private object Lexer extends StdLexical:
    override def letter = elem("letter", c => c.isLetter && c != 'λ')

However if I try // comment then all text after it is seen as whitespace. Multi-line comments however work.
Full file is here: https://github.com/atennapel/tinka-scala/blob/main/src/main/scala/Parser.scala
(I'm on Windows 11, if that's relevant)

[atennapel]

I found the issue, unrelated to Scala Parser Combinators.