import datetime
from typing import List, Dict, Optional

class Task:
    def __init__(self, description: str, deadline: Optional[str] = None):
        self.description = description
        self.deadline = deadline
        self.created_at = datetime.datetime.now()
        self.status = "scheduled"

    def to_dict(self) -> Dict:
        return {
            "description": self.description,
            "deadline": self.deadline,
            "created_at": self.created_at.isoformat(),
            "status": self.status
        }

class PlannerScheduler:
    def __init__(self):
        self.tasks: List[Task] = []

    def schedule_task(self, description: str, deadline: Optional[str] = None) -> str:
        task = Task(description, deadline)
        self.tasks.append(task)
        return f"Task '{description}' scheduled."

    def list_tasks(self, status_filter: Optional[str] = None) -> List[Dict]:
        return [t.to_dict() for t in self.tasks if status_filter is None or t.status == status_filter]

    def update_task_status(self, index: int, new_status: str) -> str:
        if 0 <= index < len(self.tasks):
            self.tasks[index].status = new_status
            return f"Task '{self.tasks[index].description}' marked as {new_status}."
        return "Invalid task index."