Minimum Delivery Agents to Fulfill All Orders Within 10-Minute SLA

Question

## Problem

You have `n` delivery orders, each with an `arrivalTime` and a required `deliveryDeadline`. Each agent can handle one order at a time and takes exactly `travelTime` minutes per delivery. Find the **minimum number of agents** needed so that all orders are delivered within their deadline.

## Example
```
orders = [{arrival:0, deadline:10}, {arrival:1, deadline:10}, {arrival:0, deadline:10}]
travelTime = 8
Output: 2
```

## Constraints
- 1 ≤ n ≤ 10^5

## Approach
Greedy interval scheduling — sort by deadline, use a min-heap to track when agents become free.

## Follow-up
Agents have a maximum shift of 4 hours. How does this affect the solution?