Add spring-outbox-kt — Transactional Outbox for Spring Boot

[BK202503]

Adds BK202503/bk-spring-outbox under category(\"Libraries/Frameworks\") { subcategory(\"Web\") { ... } } in Libraries.awesome.kts, alongside the existing run of Spring-microservice entries.

What it is

Transactional Outbox for Spring Boot as a single OutboxPublisher injection inside @Transactional:

@Transactional
fun createOrder(req: CreateOrderRequest): Order {
    val order = orderRepo.save(req.toOrder())
    outbox.publish(
        topic = \"orders\",
        aggregateType = \"Order\",
        aggregateId = order.id,
        eventType = \"OrderCreated\",
        payload = mapper.writeValueAsBytes(OrderCreated(order)),
    )
    return order
}

• Same DB transaction wraps the business write and the outbox row → atomic.
• Coroutine-based relay polls the table after commit and forwards each event to Kafka.
• PostgreSQL uses SELECT … FOR UPDATE SKIP LOCKED so multiple relay replicas don't double-publish.
• Kafka records carry outbox_event_id for downstream dedupe and aggregateId as the record key for strict per-aggregate ordering.

Project signals

• Apache-2.0 license
• Public on GitHub, v0.1.0 released 2026-06-06
• JitPack v0.1.0 builds green
• CI runs the full suite including PostgreSQL via testcontainers
• README with motivation, install, comparison, observability section, pairing recipe with spring-saga-kt

Why it fits this list

There is no Kotlin-native, Spring Boot autoconfigure-driven Transactional Outbox library in the ecosystem today. Existing options (Eventuate Tram, Debezium CDC pipelines) are Java-first or require a separate runtime. This sits naturally next to the existing Spring-microservice entries.

Checklist

• OSI-approved license (Apache-2.0)
• Public GitHub release (v0.1.0)
• Added in the matching subcategory next to similar Spring entries
• Description under 200 chars, follows the surrounding format
• Tags consistent with neighbors

Repo: https://github.com/BK202503/bk-spring-outbox
Release: https://github.com/BK202503/bk-spring-outbox/releases/tag/v0.1.0