Saga Framework Foundation

Implement the core saga framework that enables crash-recoverable multi-step operations with guaranteed compensation.

Scope

Build pkg/saga package with:

Core Interfaces:

• Action, ActionInputs, ActionFactory - stateless action pattern
• SagaDefinition, SagaExecution - saga structure and runtime state
• SagaRegistry - holds definitions and action factories registered at boot
• SagaStorage - persistence interface (entity-based implementation)

Executor:

• SagaExecutor with Execute/Compensate/Resume logic
• Durable logging after each action
• Reverse-order compensation on failure
• Recovery mechanism (query incomplete sagas, resume or compensate)

Progress Infrastructure:

• Framework-level progress callbacks via ActionInputs.Progress()
• Gracefully noop during recovery
• Route to application-provided callbacks during execution

Storage:

• SagaEntity schema (kind: saga, indexed by status)
• EntitySagaStorage implementation
• Support for querying incomplete sagas (status IN running, compensating)

Testing:

• Unit tests for executor logic (success, failure, compensation)
• Recovery scenario tests (crash simulation)
• Mock storage for fast testing

Why Foundation First

This is the framework that Issues #2 and #3 will build on. Can't meaningfully split it without creating circular dependencies.

Reference

RFD 0035: Saga Pattern for Distributed Operations Phase 1 from Migration Strategy