Technology

A pnpm monorepo: a Next.js 15 app (App Router), shared packages for types, UI, and database access, and Supabase migrations in infra/.

Stack, with reasons

• Next.js 15 + Mantine 8. One UI system, no Tailwind, by decision (ADR-0004). Mixing component systems is how design drift starts.
• Supabase (Postgres, Auth, Storage), cloud-only. No local Docker for day-to-day work (ADR-0003). 101 SQL migrations, schema-first.
• Row-level security with materialised auth columns. The enrollments table stores teacher_auth_uid and student_auth_uid directly, which removed a class of recursive RLS policies. The fix is written up in the repo.
• TanStack Query + Zod. All server state goes through typed query/mutation wrappers; all external input is validated at the boundary by schemas in a shared types package.
• Daily.co for video, Dexie (IndexedDB) for offline-first homework, Capacitor 8 for the native iOS/Android wrap.

The AI layer

• OpenAI GPT-4o for homework generation and lesson synthesis, GPT-4o-mini for classification jobs (document analysis, error tagging, word analysis). Temperature is tuned per task: 0.1 for classification, 0.7 for generation.
• DeepL for translation, plus an out-of-process spaCy service for tokenisation and lemmatisation, because POS tagging is not a job for a chat model.
• Every pipeline output is schema-validated before it touches the database, and usage is tracked for cost monitoring.

Conventions that held up

API routes follow CQRS naming (queries and commands live in separate trees), raw fetch is banned in the client, and a pre-commit hook lints any doc the commit touches.