Concepts

A concept page explains one idea that several features share, so a feature page can link to it instead of re-explaining it. Each has the same sections: what problem it solves, how it works here, a diagram, gotchas, where in code, and a self-check.

Written now (task V1)

• Testing strategy: the four test layers, what each one proves, how to run them.
• Environments & config: dev and test as they exist today (ports, database roles, env files).
• Logging (Pino): structured logs, request ids, and exactly what is redacted.

Coming

Concept	Written in
Sentry from zero	V3
CI/CD pipeline	V3
Docker & the VPS	V3
Backups	V3
Multi-tenancy & row-level security	V4
Transactions & locking	V4, V9
Authentication & sessions	V5
Authorization	V5
Validation with Zod	V5
Caching & rate limiting	V5
Money & rounding	V8
Dates & time zones	V8
Idempotency & unique constraints	V8
Background jobs & cron	V8
File uploads & signed URLs	V9
PDF generation	V9
Payment gateways & webhooks	V10
Real-time with Socket.io	V11
Notification pipeline (outbox)	V11
Web Push from zero	V11
Data lifecycle & deletion	V15
Security checklist	V16

Concepts marked "from zero" (Sentry, Web Push, and later RLS and the outbox) assume you have never met the idea before.