Halvyn

The story

Why I built it

With my partner, there was a whole layer of small everyday things (preferences, memories, instincts) that you normally only learn from each other over months, sometimes years. I didn’t want to wait. Halvyn was born from that impatience: turn mutual discovery into a game to create more complicity, faster. A space where every quiz, every mini-game and every conversation adds another brick to what we know about each other.

Structural technical decisions

Progressive dual-backend

A legacy Express server proxying /v1 to a V1 backend in clean architecture (modules / repositories / services / presenters). The monolith moves to a modern API route by route, no big-bang rewrite, no downtime.

React 18 + Capacitor monorepo

A single client codebase that ships native on iOS, Android and Web with more than 95% shared code: one design system, three platforms delivered.

Realtime couples + offline sync

WebSocket with user / couple / session rooms server-side, and an IndexedDB v3 LWW mutation queue client-side. Both partners play simultaneously and offline mutations (moods, bucket-list) replay deterministically on reconnect.

Cloudflare multi-Worker edge

Six Workers in front of the origin (rate-limiter, showcase-cache, media-CDN, cron dispatch, og-renderer, seo-localizer) absorb bursts and public traffic before it ever reaches the API.

The non-trivial challenge

Syncing a real-time quiz session for two

Each partner answers an A/B question independently, reveal only happens when both have answered, match is computed, Love Coins are distributed. And all of that has to survive a mobile disconnect mid-round, a double-answer, a partner quitting the app, or a Worker crashing.

Lesson learned

If I did it again, I would start on the V1 clean architecture from commit one instead of dragging a legacy Express alongside for months: the /v1 proxy cost more in deploy complexity and mental load than a straight rewrite would have.