--> is a valid HTML close comment when it appears on the first line of a script (Annex B). Boa rejects it unconditionally with SyntaxError.

Repro (raw script, no preceding newline):

--> this is a comment
throw new EvalError("reached");

Expected: EvalError thrown — the --> line is treated as a comment, execution continues to the next line
Got: SyntaxError

Spec: https://tc39.es/ecma262/#sec-html-like-comments

HTMLCloseComment ::
  WhiteSpaceSequence[opt] SingleLineDelimitedCommentSequence[opt] --> SingleLineCommentChars[opt]

Failing test262: annexB/language/comments/single-line-html-close-first-line-{1,2,3}.js