Executive Case Study · Layer 1 · 2 min read
Build Market — Compliance-First Construction Infrastructure
How I architected an event-driven construction marketplace, statutory verification engine, and non-custodial M-Pesa escrow platform for Kenya.
The Problem
Construction in Kenya runs on fragile offline trust:
- Unverified practitioners: Credentials across regulatory bodies (NCA, EBK, BORAQS) are claimed on paper rather than verified programmatically.
- Unprotected capital: Homeowners and diaspora investors pay large upfront deposits with zero milestone protection if work stalls.
- Unreliable statutory infrastructure: The government portals that confirm practicing licenses experience frequent downtime, timeouts, and unannounced schema drift.
The Approach
Build Market operates strictly as a technology marketplace intermediary—never a general contractor. It connects property owners, registered professionals across 30+ trades, material suppliers, and independent dispute inspectors under an audit-logged, event-driven architecture.
The Three Hardest Engineering Problems
| Challenge | Architectural Solution | Outcome |
|---|---|---|
| 1. Reliability against flaky regulator portals | 4-stage degradation pipeline: 48h verification cache → sliding-window circuit breaker → 24h NATS JetStream retry stream → two-approver human operator queue (apps/verification-ops). | User onboarding never blocks even when external NCA/EBK portals go offline. |
| 2. Money-movement correctness | Non-custodial bank trust escrow paired with idempotent M-Pesa Daraja 2.0 flows ([merchantRequestId, checkoutRequestId]), deterministic NATS message IDs, and acknowledge-only-after-commit consumers. | Process crashes or network retries can never trigger a double disbursement. |
| 3. Architectural governance on a solo team | 26 ratified ADRs enforced mechanically in CI via AST import-boundary tests, environment contract validators (75 keys), and an automated security drift scanner. | 0 security drift findings across 309 production files; strict Adapter → Service → Repo isolation. |
System Scale at a Glance
- Workspace Topology: Turborepo monorepo with 4 isolated applications (
client,admin,verification-ops,workers) and 8 shared packages (db,verification-domain,nats,resilience,redis,types,ui,enums). - Data Architecture: 114 Prisma models, 120 strict enums, 24 vertical domain slices, and Class A–D field-level data classification for Kenya DPA (2019) & GDPR compliance.
- Event Spine: 6 persistent NATS JetStream streams (
VERIFICATION,USERS,ORDERS,PROJECTS,NOTIFICATIONS,LICENSES) + isolated Node.js 24 BullMQ worker daemons. - Localized Rails: All 47 Kenyan counties, 9 statutory licensing authorities, M-Pesa STK Push / PayBill / B2C, and KRA eTIMS fiscal invoice reconciliation.