def calculate_employee_bonus(employees: list[dict], metrics: dict) -> list[dict]:
    """
    Calculate employee bonuses based on their base salary, performance rating,
    and company-wide metrics.
    
    employees: list of dicts with 'id', 'role', 'base_salary', 'rating' (1-5)
    metrics: dict with 'company_multiplier' and 'department_multipliers'
    
    Returns a list of dicts with 'id' and 'bonus'.
    """
    results = []
    
    for emp in employees:
        # BUG 1: Division by zero risk if rating is 0 or missing, and type mismatch if salary is string
        base = emp.get('base_salary', 0)
        rating = emp.get('rating', 1)
        
        # BUG 2: Incorrect logic for role based multiplier, using assignment instead of lookup
        role_mult = metrics.get('department_multipliers', {})[emp.get('role')] # will raise KeyError if role not found
        
        # Calculate base bonus
        if rating > 3:
            base_bonus = base * 0.1
        elif rating == 3:
            base_bonus = base * 0.05
        else:
            base_bonus = 0
            
        # BUG 3: Does not apply company multiplier correctly to the total
        total_bonus = base_bonus * role_mult + metrics.get('company_multiplier', 1)
        
        # BUG 4: mutating original dict instead of creating new one
        emp['bonus'] = total_bonus
        results.append(emp)
        
    return results