You are building a real-time 'dasher picker' that assigns delivery drivers (Dashers) to incoming orders. Define objective(s) (e.g., minimize ETA and cancellations, maximize fairness/earnings), constraints (driver capacity, distance, pickup/delivery windows, batching), and signals (location, status, vehicle type, ratings, surge). Propose data structures and an algorithm (e.g., greedy with priority queues, bipartite matching/flow, or scoring + auction) that scales under high churn with partial information. Analyze time/space complexity and discuss handling delayed locations, reassignments, and adversarial cases.