Enforce durable D&D evidence ranges

internal/modules/dnd/codec/sourcerange/sourcerange.go

@@ -0,0 +1,24 @@
+// Package sourcerange validates durable D&D source-reference ranges.
+package sourcerange
+
+import (
+	"fmt"
+
+	"gitea.maximumdirect.net/eric/notarius/internal/core/source"
+)
+
+// Validate checks the source-independent numeric constraints of a durable
+// source reference. Source membership and extraction-chunk coverage require
+// source context and remain the responsibility of source-aware validators.
+func Validate(ref source.SourceRef) error {
+	if ref.StartUnitID <= 0 {
+		return fmt.Errorf("start_unit_id must be positive")
+	}
+	if ref.EndUnitID <= 0 {
+		return fmt.Errorf("end_unit_id must be positive")
+	}
+	if ref.StartUnitID > ref.EndUnitID {
+		return fmt.Errorf("start_unit_id must not exceed end_unit_id")
+	}
+	return nil
+}