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A complete system design walkthrough for a verified badge identity-verification program at scale: applicant intake, encrypted evidence storage, asynchronous fan-out pipeline (document forensics, liveness/face-match, deduplication, eligibility, risk scoring), three-lane decision routing (auto-approve / human review / auto-reject), badge issuance, tamper-evident audit log, appeals, and data-minimising retention — with inline SVG…

A complete system design walkthrough for a Try Before You Buy apparel marketplace: saga-coordinated trial orders, card authorisation holds, soft and hard inventory reservation, order and return state machines, automated pickup scheduling, courier anti-corruption adapters, warehouse QC, refund and restock flow, capacity estimation, security, and fraud prevention — illustrated with…

A complete, beginner-to-production system design walkthrough for handling supplier inventory feed delays and failures without ever overselling: circuit breakers, safety stock buffers, Kafka-backed ingestion pipelines, reservation with optimistic locking, reconciliation jobs, and end-to-end monitoring, illustrated with inline architecture and sequence diagrams and Java code.