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
+}

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

@@ -0,0 +1,31 @@
+package sourcerange
+
+import (
+	"strings"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/notarius/internal/core/source"
+)
+
+func TestValidateChecksOnlyDurableNumericRange(t *testing.T) {
+	for _, test := range []struct {
+		name string
+		ref  source.SourceRef
+		want string
+	}{
+		{name: "valid without source ID", ref: source.SourceRef{StartUnitID: 1, EndUnitID: 2}},
+		{name: "nonpositive start", ref: source.SourceRef{StartUnitID: 0, EndUnitID: 1}, want: "start_unit_id"},
+		{name: "nonpositive end", ref: source.SourceRef{StartUnitID: 1, EndUnitID: 0}, want: "end_unit_id"},
+		{name: "reversed", ref: source.SourceRef{StartUnitID: 2, EndUnitID: 1}, want: "must not exceed"},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			err := Validate(test.ref)
+			if test.want == "" && err != nil {
+				t.Fatalf("Validate() error = %v, want nil", err)
+			}
+			if test.want != "" && (err == nil || !strings.Contains(err.Error(), test.want)) {
+				t.Fatalf("Validate() error = %v, want %q", err, test.want)
+			}
+		})
+	}
+}