Tech Context

Primary Stack

Frontend: Next.js 15 (App Router) + React 19 + TypeScript, styled with handcrafted CSS for now (Tailwind/shadcn still optional future add-ons).
Backend Worker: Node.js service run with tsx, using youtubei.js for Innertube chat ingestion, fastify + @fastify/cors for REST/SSE transport, and eventemitter3 for internal pub/sub.
Shared Types: Simple TypeScript module in shared/chat.ts, imported via the @shared/* path alias defined in tsconfig.base.json.
Realtime: Server-Sent Events for overlay updates; WebSockets remain a future enhancement option.
Timezone Handling: Browser timezone detection via Intl.DateTimeFormat().resolvedOptions().timeZone with GMT+3 fallback for international users.

Single root package.json; pnpm install manages all deps.
pnpm dev runs backend (tsx backend/src/index.ts) and client (next dev client) concurrently via concurrently.
pnpm build compiles the backend with tsc and builds the Next app; pnpm start:backend / pnpm start:client serve production bundles separately.

Requires YOUTUBE_LIVE_ID (or full URL) to enable real chat ingestion; omitted value triggers mock mode.
Optional overrides for Innertube API keys/version can be supplied through env vars when needed.
better-sqlite3 is included for future persistence work but not yet wired in.

Innertube endpoints may break; keep ingestion module adaptable and plan for a headless-browser fallback.
Project expected to run on the streamer’s machine; dependencies must remain cross-platform and avoid heavyweight native builds where possible.
No separate package boundaries anymore, so TypeScript path aliases and import hygiene are important to prevent tangled relative paths.