How would you make instant grocery substitution and availability reliable during peak demand?

Problem Statement Description

Blinkit operates in a high-expectation quick-commerce environment where customers expect groceries to arrive within tight delivery windows and with minimal surprises. During peak demand periods, such as evenings, weekends, festivals, rain, or promotional events, item availability can change rapidly inside dark stores, creating mismatches between what customers see in the app and what pickers can actually fulfill.

For this Technical PM problem, focus on how to make the substitution and availability experience reliable when inventory is volatile and operational teams are under pressure. The workflow spans customer product discovery, cart building, checkout, inventory reservation, picker actions, substitution decisions, customer communication, and final delivery.

Assume the target users are premium quick-commerce customers who value speed, accuracy, and trust, as well as internal users such as pickers, store managers, inventory systems, and customer support teams. Your scope should cover both customer-facing experience and backend/platform capabilities needed to support dependable on-time fulfilled orders.

The experience should consider:

- Real-time or near-real-time inventory accuracy across app, warehouse, and picker workflows

- How substitution preferences, customer consent, and unavailable-item handling should work during checkout and fulfillment

- APIs, data flows, and system dependencies between catalog, inventory, order management, picker app, and delivery operations

- Reliability requirements during peak demand, including latency, freshness, fallback behavior, and degraded-mode handling

- Privacy, data quality, and responsible use of customer preferences or past purchase signals

- Operational load on pickers and dark-store staff, especially when many orders require exception handling

- Observability, alerts, metrics, and debugging tools to detect inventory mismatch or substitution failures

- Rollout, experimentation, risk management, and trade-offs between speed, accuracy, customer control, and cost

The goal is to describe how you would define the technical product requirements and operating approach for a reliable substitution and availability system that preserves customer trust while improving on-time fulfilled orders during peak demand.