Public SPI for WoGu: the WorkflowValidator contract, the Rule/RuleCategory metadata WoGu is organized around, and the immutable model types (ValidationContext, RuleResult, ValidatorRunOutcome, ValidationSummary, Violation, CallPathFrame, Severity) that every workflow-engine integration (Temporal, and future Conductor/ Camunda/Airflow modules) is built against. This module has zero dependency on any workflow engine, parser, or build tool.