Unified logical-plan IR, optimizer, and parser-plugin registry.

kyma-plan's [LogicalPlan][logical_plan::LogicalPlan] is the frontend-neutral IR that every [kyma_core::query_frontend::QueryFrontend] produces and that kyma-exec lowers to DataFusion.

Module map

• [logical_plan] — the unified plan enum (frontend-neutral).
• [optimizer] — rewrite rules (telemetry-specific + generic).
• [query_frontend_registry] — routes queries by Content-Type to the right registered frontend and unpacks its opaque plan.