Core trait for all computation nodes in the fact-graph engine. Defines an Expression/Operator hierarchy (Add, Sum, Maximum, Switch, Placeholder, Match, etc.) that models tax logic as a directed acyclic graph of derived and writable facts. Each node is typed with domain-specific wrappers (Dollar, Day, Tin, Ein, IpPin) and supports lazy evaluation, cycle detection, and serialization. This pattern is reusable for any declarative business rule system where rules need to be shared between server and browser (compiled to JS via Scala.js).

A generic, versioned message router for SQS/SNS queue messages. Maintains a Map<MessageVersion, Handler> and routes incoming JSON payloads to the appropriate handler based on a version header, with an UnsupportedMessageVersionHandler fallback. This pattern is replicated across submission confirmation, dispatch, email, and pending submission routers, demonstrating a clean, maintainable approach to handling evolving message contracts in a microservices environment. Could be extracted as a library for any system using versioned async messages.

An abstraction over different I/O locations for reading/writing resources (classpath, filesystem directory, S3-like document store, in-memory). The IOLocation interface provides a uniform API (read, write, list, delete) with configurable location types via StorageLocationBuilder. This decouples services from specific storage backends, enabling easy switching between local development (DirectoryIOLocation, MemoryIOLocation) and production (DocumentStoreIOLocation backed by S3). The pattern is directly reusable for any application needing flexible file storage without hardcoding providers.

A centralized audit logging service using MDC (Mapped Diagnostic Context) with structured event properties. The @Auditable annotation on methods triggers automatic audit log creation with principal, event type, and custom properties. The AuditLogElement is a JSON-serializable record. This pattern ensures consistent, searchable audit trails across all services without scattering logging code. Reusable for any application requiring compliance-grade audit logging with minimal intrusion.

A React component that renders rich text content from i18n keys, supporting embedded links (internal, external, modal triggers, images) via a custom link renderer. It separates content structure (translation keys with HTML-like tags) from presentation (allowed tags, link behavior). This is a polished, reusable solution for applications that need to display dynamically translated content with safe HTML rendering and custom link handling, especially in multi-language contexts.