Lumen is a realtime analytics platform for DTC e-commerce brands — pipeline ingestion from Shopify, BigQuery, and Stripe; cohort analysis; revenue attribution. **Challenge:** The founder had a working MVP but it couldn't handle Black Friday traffic — the Lambda cold starts broke the dashboard, and PostgreSQL aggregations took 30+ seconds. **Approach:** Rebuilt the ingest path on Cloudflare Workers + R2; rewrote aggregations as incremental materialized views on ClickHouse; replaced the dashboard with Next.js + D3. **Outcome:** - 99.95% ingest reliability under 10× Black Friday peak - Dashboard p99 latency 0.9s (was 30s) - $212k ARR in the first 6 months post-launch