Simulation-style coding problem with scaling follow-up (mini system design)

Implement a simulation-style program: given an initial state and a sequence of events/operations, update the system state in order and output the final result and/or per-step outputs. Requirements: First, state and justify your assumed input format (initial parameters, event list, fields per event). Clearly define the output. Provide time/space complexity. Follow-up (scale up): if the number of events and data size grow significantly, or the system must support high concurrency/distributed processing, describe how you would evolve the design: Algorithm/data-structure optimizations; Batch vs streaming; Concurrency control and consistency; Sharding, queues, caching, fault tolerance, and observability. Note: since the original prompt is missing, present your solution as a reusable simulation framework with pluggable rule interfaces.