(HN/ HCM) Senior Fullstack Engineer (AI)

Description
Crossian is a high-growth technology-driven e-commerce business. As a start-up formed in 2020, we have created a fast-paced and dynamic environment, enabling our people to reach a cumulative average growth rate of over 1000% in the last 5 years.
We're forming an elite Fullstack squad that operates differently, working with AI-driven products. No "that's not my ticket" culture. Each engineer owns a feature end-to-end - from data model to UI pixel - and thinks like a Product Owner when scoping, like a Solutions Architect when designing, and like a craftsman when coding.
If you want to work with people like that and become like them, this is the next step.
What you'll do
Feature ownership
Take a feature from kick-off to production: data model, API design, service layer, UI.
Own reliability, performance, and observability of what you ship - not just the happy path.
Turn product goals into concrete technical specs.
System design & architecture
Design full-stack architectures: databases, APIs, queues, caches, frontend rendering strategies.
Apply patterns (Clean Architecture, Event - Driven, etc) where they fit the problem.
Write design docs and lead technical discussions.
Backend
Build well-tested APIs and microservices in [protected info], Go, or Python - whichever fits.
Design and optimize relational and non-relational databases.
Work with event streaming.
Frontend
Build fast, accessible, SEO-friendly storefronts with React / [protected info] (SSR/CSR as appropriate).
Optimize Core Web Vitals, bundle size, lazy loading, and CDN strategy (Cloudflare, AWS S3).
Write maintainable state management (Redux, Zustand, Recoil).
Code quality & collaboration
Write clean, tested, well-structured code; review teammates' code.
Treat unit/integration/e2e testing and CI/CD as standard practice.
Work with Product and Design to shape requirements, not just receive them.
Support junior engineers
Requirements
Education & Experience
Education: Strong academic background in Computer Science, Engineering,...
5+ years of professional engineering with real fullstack work. We value T-shaped engineers who have a clear spike (deep expertise) in either Frontend or Backend, but possess the full-stack capability to own and ship a feature end-to-end when needed
2+ years building products at a product company, fast-growing tech startup, or environments demanding strong product-led delivery.
Built or joined at least one system from scratch: schema, API, service, and UI.
Technical Depth & Domain Knowledge
We don't gate-keep on language, but you should understand the why behind your choices.
Must have at least one stack in depth:
TypeScript / JavaScript: [protected info], React, [protected info] (SSR, API routes, state management),
Node / Go / Java: backend services, goroutines, clean service architecture
Python: API backends, scripting, data-adjacent services
LLM / AI integration in production features
Databases (required):
Relational design: normalization, indexing, query optimization, transactions (PostgreSQL preferred)
At least one NoSQL store in production (Redis, MongoDB, Elasticsearch)
Able to diagnose and fix a slow query
System-level:
Async systems: queues, events, background workers
Judgment on when caching helps vs. when it creates problems
Monolith and Microservice trade offs
Nice to have:
eCommerce: checkout flows, inventory, pricing engines, ad integrations
Docker, Kubernetes basics, CI/CD pipeline ownership
Benefits
Ownership: Direct ownership of real work streams from day 1 with a clear trajectory toward product leadership roles.
AI Implementation: Hands-on experience deploying cutting-edge AI solutions to solve high-scale business problems.
High-performance Team: Work with a data-driven team that values autonomy, speed, and outcomes.
Compensation: Competitive total compensation package (13 months guarantee + attractive bonus).
Health & Leave: 15 paid leave days + global health insurance.
Learning Budget: Dedicated L&D budget to support your professional development.