Contract Principal Software Engineer (Java Spring)

About the Company: Stable Kernel is a technology services firm and custom software developer building scalable software solutions for cutting-edge, innovative enterprises to move their business forward. We are headquartered in Atlanta, GA. We’re a privately held, Great Place to Work Certified Company™ with a multi-award-winning culture and an impressive 10-plus-year trajectory of sustainable growth. At Stable Kernel, we support our employees in ways that help them do some of the best work of their lives. About the Role: As a Stable Kernel Contract Principal Software Engineer , you play an essential role in setting our portfolio of world-class clients up for success through the development and delivery of their most innovative, transformational initiatives. You will collaborate daily with other engineers and product team members, make decisions that influence the path of a product roadmap, leverage software development best practices, and become a more well-rounded engineer as you learn new technologies. Your knowledgeable practice, reliability, and consultative nature make you an engineer that stakeholders and teammates trust. Core Responsibilities Include: Technical Impact: Design and implement loyalty engine services in Java using the Spring framework, including transaction processing, tier calculation, reward accrual, and benefit eligibility. Design and implement RESTful API services in Java using the Spring framework, following contract-first development practices, with a focus on aggregation patterns, caching strategies, circuit breaking, and graceful degradation for latency-sensitive flows. Modern Java (17+) and familiarity with current Spring Boot conventions, including reactive patterns where appropriate. Cloud platform experience (AWS, GCP, or Azure), including service deployment, networking fundamentals, and managed services such as queues, caches, and databases. Identity and access management protocols such as OAuth 2.0, OIDC, and SAML, including integration with enterprise identity providers and directory services. Establishing and evolving service architecture, including domain modeling, rules evaluation patterns, event-driven state management, auditability, API versioning, and backward-compatibility standards that support independent mobile release cadences. Defining integration contracts with upstream enterprise platforms (POS, CRM, commerce, identity providers) and downstream consumers (BFF, analytics, finance), including data normalization, error mapping, and retry logic. Building and maintaining integrations that pull transaction data from multiple channels and apply consistent earning logic regardless of source. Authentication and session management patterns, including token refresh, device trust, and silent re-authentication for long-lived mobile sessions. Implementing cross-cutting concerns such as idempotency, correlation IDs, observability, and audit event emission. Implementing robust state management for account-level aggregations, provisional and finalized reward states, and period-based accrual tracking. Designing test strategies for complex business rules, including edge cases around split-tier earning, return adjustments, forward offsets, delegate activity aggregation, and high system reliability. Implementing security and audit concerns: role-based access, 2FA for redemption flows, full audit trails for all state changes. Designing and involving yourself in CI/CD and automated testing for high system reliability. Providing expert feedback that improves the overall delivery of work and ensuring a high standard of quality across the project. Using AI-assisted development tools such as Claude Code or Cursor to accelerate delivery while maintaining code quality and architectural standards. Business Alignment: Clarifying strategic outcomes and influencing roadmaps and projects. Identifying, suggesting, and driving improvements in your customers' end-to-end experience. Aiding in estimating work for new…