lila/documentation/decisions.md

Decisions Log

A record of non-obvious technical decisions made during development, with reasoning. Intended to preserve context across sessions.

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Tooling

Monorepo: pnpm workspaces (not Turborepo)

Turborepo adds parallel task running and build caching on top of pnpm workspaces. For a two-app monorepo of this size, plain pnpm workspace commands are sufficient and there is one less tool to configure and maintain.

TypeScript runner: tsx (not ts-node)

tsx is faster, requires no configuration, and uses esbuild under the hood. ts-node is older and more complex to configure. tsx does not do type checking — that is handled separately by tsc and the editor. Installed as a dev dependency in apps/api only.

ORM: Drizzle (not Prisma)

Drizzle is lighter — no binary, no engine. Queries map closely to SQL. Migrations are plain SQL files. Works naturally with Zod for type inference. Prisma would add Docker complexity (engine binary in containers) and abstraction that is not needed for this schema.

WebSocket: ws library (not Socket.io)

For rooms of 2–4 players, Socket.io's room management, transport fallbacks, and reconnection abstractions are unnecessary overhead. The WS protocol is defined explicitly as a Zod discriminated union in packages/shared, giving the same type safety guarantees. Reconnection logic is deferred to Phase 7.

Auth: OpenAuth (not rolling own JWT)

All auth delegated to OpenAuth service at auth.yourdomain.com. Providers: Google, GitHub. The API validates the JWT on every protected request. User rows are created or updated on first login via the sub claim as the primary key.

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Docker

Multi-stage builds for monorepo context

Both apps/web and apps/api use multi-stage Dockerfiles (deps, dev, builder, runner) because:

• The monorepo structure requires copying pnpm-workspace.yaml, root package.json, and cross-dependencies (packages/shared, packages/db) before installing
• node_modules paths differ between host and container due to workspace hoisting
• Stages allow caching pnpm install separately from source code changes

Vite as dev server (not Nginx)

In development, apps/web uses vite dev directly, not Nginx. Reasons:

• Hot Module Replacement (HMR) requires Vite's WebSocket dev server
• Source maps and error overlay need direct Vite integration
• Nginx would add unnecessary proxy complexity for local dev

Production will use Nginx to serve static Vite build output.

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Architecture

Express app structure: factory function pattern

app.ts exports a createApp() factory function. server.ts imports it and calls .listen(). This allows tests to import the app directly without starting a server, keeping tests isolated and fast.

Data model: decks separate from terms (not frequency_rank filtering)

Original approach: Store frequency_rank on terms table and filter by rank range for difficulty.

Problem discovered: WordNet/OMW frequency data is unreliable for language learning. Extraction produced results like:

• Rank 1: "In" → "indio" (chemical symbol: Indium)
• Rank 2: "Be" → "berillio" (chemical symbol: Beryllium)
• Rank 7: "He" → "elio" (chemical symbol: Helium)

These are technically "common" in WordNet (every element is a noun) but useless for vocabulary learning.

Decision:

• terms table stores ALL available OMW synsets (raw data, no frequency filtering)
• decks table stores curated learning lists (A1, A2, B1, "Most Common 1000", etc.)
• deck_terms junction table links terms to decks with position ordering
• rooms.deck_id specifies which vocabulary deck a game uses

Benefits:

• Curricula can come from external sources (CEFR lists, Oxford 3000, SUBTLEX)
• Bad data (chemical symbols, obscure words) excluded at deck level, not schema level
• Users can create custom decks later
• Multiple difficulty levels without schema changes

Multiplayer mechanic: simultaneous answers (not buzz-first)

All players see the same question at the same time and submit independently. The server waits for all answers or a 15-second timeout, then broadcasts the result. This keeps the experience Duolingo-like and symmetric. A buzz-first mechanic was considered and rejected.

Room model: room codes (not matchmaking queue)

Players create rooms and share a human-readable code (e.g. WOLF-42) to invite friends. Auto-matchmaking via a queue is out of scope for MVP. Valkey is included in the stack and can support a queue in a future phase.

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TypeScript Configuration

Base config: no lib, module, or moduleResolution

These are intentionally omitted from tsconfig.base.json because different packages need different values — apps/api uses NodeNext, apps/web uses ESNext/bundler (Vite), and mixing them in the base caused errors. Each package declares its own.

outDir: "./dist" per package

The base config originally had outDir: "dist" which resolved relative to the base file location, pointing to the root dist folder. Overridden in each package with "./dist" to ensure compiled output stays inside the package.

apps/web tsconfig: deferred to Vite scaffold

The web tsconfig was left as a placeholder and filled in after pnpm create vite generated tsconfig.json, tsconfig.app.json, and tsconfig.node.json. The generated files were then trimmed to remove options already covered by the base.

rootDir: "." on apps/api

Set explicitly to allow vitest.config.ts (which lives outside src/) to be included in the TypeScript program. Without it, TypeScript infers rootDir as src/ and rejects any file outside that directory.

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ESLint

Two-config approach for apps/web

The root eslint.config.mjs handles TypeScript linting across all packages. apps/web/eslint.config.js is kept as a local addition for React-specific plugins only: eslint-plugin-react-hooks and eslint-plugin-react-refresh. ESLint flat config merges them automatically by directory proximity — no explicit import between them needed.

Coverage config at root only

Vitest coverage configuration lives in the root vitest.config.ts only. Individual package configs omit it to produce a single aggregated report rather than separate per-package reports.

globals: true with "types": ["vitest/globals"]

Using Vitest globals (describe, it, expect without imports) requires "types": ["vitest/globals"] in each package's tsconfig compilerOptions. Added to apps/api, packages/shared, and packages/db. Added to apps/web/tsconfig.app.json.

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Known Issues / Dev Notes

glossa-web has no healthcheck

The web service in docker-compose.yml has no healthcheck defined. Reason: Vite's dev server (vite dev) has no built-in health endpoint. Unlike the API's /api/health, there's no URL to poll.

Workaround: depends_on uses api healthcheck as proxy. For production (Nginx), add a health endpoint or use TCP port check.

Valkey memory overcommit warning

Valkey logs this on start in development:

WARNING Memory overcommit must be enabled for proper functionality

This is harmless in dev but should be fixed before production. The warning appears because Docker containers don't inherit host sysctl settings by default.

Fix: Add to host /etc/sysctl.conf:

vm.overcommit_memory = 1

Then sudo sysctl -p or restart Docker.

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Data Model

Users: internal UUID + openauth_sub (not sub as PK)

Original approach: Use OpenAuth sub claim directly as users.id (text primary key).

Problem: Embeds auth provider in the primary key (e.g. "google|12345"). If OpenAuth changes format or a second provider is added, the PK cascades through all FKs (rooms.host_id, room_players.user_id).

Decision:

• users.id = internal UUID (stable FK target)
• users.openauth_sub = text UNIQUE (auth provider claim)
• Allows adding multiple auth providers per user later without FK changes

Rooms: updated_at for stale recovery only

Most tables omit updated_at (unnecessary for MVP). rooms.updated_at is kept specifically for stale room recovery—identifying rooms stuck in in_progress status after server crashes.

Translations: UNIQUE (term_id, language_code, text)

Allows multiple synonyms per language per term (e.g. "dog", "hound" for same synset). Prevents exact duplicate rows. Homonyms (e.g. "Lead" metal vs. "Lead" guide) are handled by different term_id values (different synsets), so no constraint conflict.

Decks: pair_id is nullable

decks.pair_id references language_pairs but is nullable. Reasons:

• Single-language decks (e.g. "English Grammar")
• Multi-pair decks (e.g. "Cognates" spanning EN-IT and EN-FR)
• System decks (created by app, not tied to specific user)

Decks separate from terms (not frequency_rank filtering)

Original approach: Store frequency_rank on terms table and filter by rank range for difficulty.

Problem discovered: WordNet/OMW frequency data is unreliable for language learning. Extraction produced results like:

• Rank 1: "In" → "indio" (chemical symbol: Indium)
• Rank 2: "Be" → "berillio" (chemical symbol: Beryllium)
• Rank 7: "He" → "elio" (chemical symbol: Helium)

These are technically "common" in WordNet (every element is a noun) but useless for vocabulary learning.

Decision:

• terms table stores ALL available OMW synsets (raw data, no frequency filtering)
• decks table stores curated learning lists (A1, A2, B1, "Most Common 1000", etc.)
• deck_terms junction table links terms to decks with position ordering
• rooms.deck_id specifies which vocabulary deck a game uses

Benefits:

• Curricula can come from external sources (CEFR lists, Oxford 3000, SUBTLEX)
• Bad data (chemical symbols, obscure words) excluded at deck level, not schema level
• Users can create custom decks later
• Multiple difficulty levels without schema changes

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Current State

Completed checkboxes (Phase 0)

• Initialise pnpm workspace monorepo: apps/web, apps/api, packages/shared, packages/db
• Configure TypeScript project references across packages
• Set up ESLint + Prettier with shared configs in root
• Set up Vitest in api and web and both packages
• Scaffold Express app with GET /api/health
• Scaffold Vite + React app with TanStack Router (single root route)
• Configure Drizzle ORM + connection to local PostgreSQL
• Write first migration (empty — just validates the pipeline works)
• docker-compose.yml for local dev: api, web, postgres, valkey
• .env.example files for apps/api and apps/web
• update decisions.md

Phase 0 is finished with this.

Current checkpoint

• Run scripts/extract_omw.py locally → generates packages/db/src/seed.json