"""Strict browser decision request contract; values and UI mechanics stay in Node."""
def validate_request(payload):
    if not isinstance(payload,dict) or set(payload)!={'states'}:
        raise ValueError('Expected {"states": [...]}')
    states=payload['states']
    if not isinstance(states,list) or not 1<=len(states)<=32:
        raise ValueError('Expected 1–32 states')
    seen=set();question_count=path_count=0
    for state in states:
        if not isinstance(state,dict) or set(state)!={'id','state','questions'}:
            raise ValueError('Each state requires id, state, questions')
        sid=state['id']
        if not isinstance(sid,str) or not sid.strip() or sid in seen:
            raise ValueError('State IDs must be unique nonempty strings')
        seen.add(sid)
        if not isinstance(state['state'],(str,dict,list)) or not state['state']:
            raise ValueError('State must be nonempty text, object or list')
        questions=state['questions']
        if not isinstance(questions,dict) or not questions:
            raise ValueError('Questions must be a nonempty object')
        for qid,q in questions.items():
            if not isinstance(qid,str) or not qid.strip() or not isinstance(q,dict):
                raise ValueError('Invalid question')
            if set(q)!={'type','instructions','criteria'} or q['type']!='choice':
                raise ValueError('Browser API supports choice questions only')
            if not isinstance(q['instructions'],str) or not q['instructions'].strip():
                raise ValueError('Instructions must be nonempty text')
            criteria=q['criteria']
            if not isinstance(criteria,dict) or not 2<=len(criteria)<=255:
                raise ValueError('Expected 2–255 candidate actions')
            if any(not isinstance(k,str) or not k.strip() or not isinstance(v,str) or not v.strip() for k,v in criteria.items()):
                raise ValueError('Candidate IDs and descriptions must be nonempty text')
            question_count+=1;path_count+=len(criteria)
    if question_count>96 or path_count>256:
        raise ValueError('Request exceeds 96 questions or 256 candidate paths')
    return states