Milestone: Backends and Persistence

[niteshpurohit]

Summary

Implement the shared backend contract and the concrete backend support needed for Karya to run consistently across its supported persistence options.

Scope

• implement the shared backend interface, backend selection model, capability reporting, and parity boundaries
• deliver the supported backend implementations and bring InMemory into parity with the final shared backend contract
• implement and validate persistence parity for schedules, workflows, audit-relevant data, and backend-specific failure behavior
• publish backend comparison and selection guidance grounded in the implemented backend model

Child Work

• shared backend contract and selection model
• backend implementations and InMemory parity
• persistence parity and backend-specific validation
• backend comparison and support guidance

Acceptance Criteria

• backend integrations implement one shared contract rather than diverging per adapter
• supported backends are runnable, validated, and explicit about parity guarantees and exceptions
• framework, operator, workflow, and governance work can rely on documented backend capabilities instead of implicit assumptions