diff --git a/internal/modules/dnd/shared/citations.go b/internal/modules/dnd/shared/citations.go
index 97e80e6..f8b129f 100644
--- a/internal/modules/dnd/shared/citations.go
+++ b/internal/modules/dnd/shared/citations.go
@@ -7,27 +7,37 @@ import (
 	"gitea.maximumdirect.net/eric/notarius/internal/core/source"
 )
 
+// CitationResolver resolves cited ranges against one source document.
+type CitationResolver struct {
+	doc   *source.SourceDocument
+	index source.DocumentIndex
+}
+
+// NewCitationResolver prepares citation resolution for doc.
+func NewCitationResolver(doc *source.SourceDocument) (*CitationResolver, error) {
+	if doc == nil {
+		return nil, fmt.Errorf("source document must not be nil")
+	}
+	return &CitationResolver{doc: doc, index: source.NewDocumentIndex(doc)}, nil
+}
+
 // CitedText resolves cited source ranges in document order, including each
 // source unit once, and joins the resulting text with newlines.
-func CitedText(doc *source.SourceDocument, refs []source.SourceRef) (string, error) {
-	if doc == nil {
-		return "", fmt.Errorf("source document must not be nil")
-	}
-
-	included := make([]bool, len(doc.Units))
+func (r *CitationResolver) CitedText(refs []source.SourceRef) (string, error) {
+	included := make([]bool, len(r.doc.Units))
 	for _, ref := range refs {
-		if err := source.ValidateRef(doc, ref); err != nil {
+		if err := r.index.ValidateRef(ref); err != nil {
 			return "", fmt.Errorf("resolve cited source range: %w", err)
 		}
-		start, _ := source.UnitIndex(doc, ref.StartUnitID)
-		end, _ := source.UnitIndex(doc, ref.EndUnitID)
+		start, _ := r.index.Position(ref.StartUnitID)
+		end, _ := r.index.Position(ref.EndUnitID)
 		for index := start; index <= end; index++ {
 			included[index] = true
 		}
 	}
 
-	parts := make([]string, 0, len(doc.Units))
-	for index, unit := range doc.Units {
+	parts := make([]string, 0, len(r.doc.Units))
+	for index, unit := range r.doc.Units {
 		if included[index] {
 			parts = append(parts, unit.Text)
 		}
diff --git a/internal/modules/dnd/shared/citations_test.go b/internal/modules/dnd/shared/citations_test.go
index cf41b6a..7a090de 100644
--- a/internal/modules/dnd/shared/citations_test.go
+++ b/internal/modules/dnd/shared/citations_test.go
@@ -7,8 +7,12 @@ import (
 	"gitea.maximumdirect.net/eric/notarius/internal/core/source"
 )
 
-func TestCitedText(t *testing.T) {
+func TestCitationResolver(t *testing.T) {
 	doc := citationDocument()
+	resolver, err := NewCitationResolver(doc)
+	if err != nil {
+		t.Fatalf("NewCitationResolver() error = %v", err)
+	}
 	tests := []struct {
 		name    string
 		refs    []source.SourceRef
@@ -51,7 +55,7 @@ func TestCitedText(t *testing.T) {
 		t.Run(test.name, func(t *testing.T) {
 			beforeUnits := append([]source.SourceUnit(nil), doc.Units...)
 			refs := append([]source.SourceRef(nil), test.refs...)
-			got, err := CitedText(doc, refs)
+			got, err := resolver.CitedText(refs)
 			if (err != nil) != test.wantErr {
 				t.Fatalf("CitedText() error = %v, want error = %t", err, test.wantErr)
 			}
@@ -65,9 +69,9 @@ func TestCitedText(t *testing.T) {
 	}
 }
 
-func TestCitedTextRejectsNilDocument(t *testing.T) {
-	if _, err := CitedText(nil, nil); err == nil {
-		t.Fatal("CitedText() error = nil, want nil-document error")
+func TestNewCitationResolverRejectsNilDocument(t *testing.T) {
+	if _, err := NewCitationResolver(nil); err == nil {
+		t.Fatal("NewCitationResolver() error = nil, want nil-document error")
 	}
 }
 
diff --git a/internal/modules/dnd/validate/combatturns/source_relatedness/validator.go b/internal/modules/dnd/validate/combatturns/source_relatedness/validator.go
index e9848a9..8f4a461 100644
--- a/internal/modules/dnd/validate/combatturns/source_relatedness/validator.go
+++ b/internal/modules/dnd/validate/combatturns/source_relatedness/validator.go
@@ -37,10 +37,14 @@ func (v *Validator) Validate(_ context.Context, req contracts.TypedValidationReq
 	if combatshape.Validate(req.Value) != nil {
 		return contracts.ValidationResult{Approved: true}, nil
 	}
+	resolver, err := shared.NewCitationResolver(req.Source)
+	if err != nil {
+		return contracts.ValidationResult{Approved: true}, nil
+	}
 
 	citedTexts := make([]string, len(req.Value.CombatTurns))
 	for turnIndex, turn := range req.Value.CombatTurns {
-		citedText, err := shared.CitedText(req.Source, turn.SourceRefs)
+		citedText, err := resolver.CitedText(turn.SourceRefs)
 		if err != nil {
 			return contracts.ValidationResult{Approved: true}, nil
 		}
diff --git a/internal/modules/dnd/validate/npcinteractions/source_relatedness/validator.go b/internal/modules/dnd/validate/npcinteractions/source_relatedness/validator.go
index 02d6fdf..a5b8465 100644
--- a/internal/modules/dnd/validate/npcinteractions/source_relatedness/validator.go
+++ b/internal/modules/dnd/validate/npcinteractions/source_relatedness/validator.go
@@ -39,9 +39,13 @@ func (v *Validator) Validate(_ context.Context, req contracts.TypedValidationReq
 	if interactionshape.Validate(req.Value) != nil {
 		return contracts.ValidationResult{Approved: true}, nil
 	}
+	resolver, err := shared.NewCitationResolver(req.Source)
+	if err != nil {
+		return contracts.ValidationResult{Approved: true}, nil
+	}
 	citedTexts := make([]string, len(req.Value.Interactions))
 	for index, interaction := range req.Value.Interactions {
-		citedText, err := shared.CitedText(req.Source, interaction.SourceRefs)
+		citedText, err := resolver.CitedText(interaction.SourceRefs)
 		if err != nil {
 			return contracts.ValidationResult{Approved: true}, nil
 		}
diff --git a/internal/modules/dnd/validate/npcs/source_relatedness/validator.go b/internal/modules/dnd/validate/npcs/source_relatedness/validator.go
index 339d195..6ceb258 100644
--- a/internal/modules/dnd/validate/npcs/source_relatedness/validator.go
+++ b/internal/modules/dnd/validate/npcs/source_relatedness/validator.go
@@ -37,9 +37,13 @@ func (v *Validator) Validate(_ context.Context, req contracts.TypedValidationReq
 	if err := npcshape.Validate(req.Value); err != nil {
 		return contracts.ValidationResult{Approved: true}, nil
 	}
+	resolver, err := shared.NewCitationResolver(req.Source)
+	if err != nil {
+		return contracts.ValidationResult{Approved: true}, nil
+	}
 	citedTexts := make([]string, len(req.Value.NPCs))
 	for npcIndex, npc := range req.Value.NPCs {
-		citedText, err := shared.CitedText(req.Source, npc.SourceRefs)
+		citedText, err := resolver.CitedText(npc.SourceRefs)
 		if err != nil {
 			return contracts.ValidationResult{Approved: true}, nil
 		}
diff --git a/internal/modules/dnd/validate/scenedescriptions/source_relatedness/validator.go b/internal/modules/dnd/validate/scenedescriptions/source_relatedness/validator.go
index e2d23ac..29b28b9 100644
--- a/internal/modules/dnd/validate/scenedescriptions/source_relatedness/validator.go
+++ b/internal/modules/dnd/validate/scenedescriptions/source_relatedness/validator.go
@@ -48,9 +48,13 @@ func (v *Validator) Validate(_ context.Context, req contracts.TypedValidationReq
 	if shape.Validate(req.Value) != nil || !sourceRefsValid(req.Source, req.Value) {
 		return contracts.ValidationResult{Approved: true}, nil
 	}
+	resolver, err := shared.NewCitationResolver(req.Source)
+	if err != nil {
+		return contracts.ValidationResult{Approved: true}, nil
+	}
 	warnings := make([]contracts.Warning, 0)
 	for index, scene := range req.Value.Scenes {
-		citedText, err := shared.CitedText(req.Source, []source.SourceRef{scene.SourceRef})
+		citedText, err := resolver.CitedText([]source.SourceRef{scene.SourceRef})
 		if err != nil {
 			return contracts.ValidationResult{Approved: true}, nil
 		}
diff --git a/internal/modules/dnd/validate/spells/source_relatedness/validator.go b/internal/modules/dnd/validate/spells/source_relatedness/validator.go
index aafa0d9..96eded7 100644
--- a/internal/modules/dnd/validate/spells/source_relatedness/validator.go
+++ b/internal/modules/dnd/validate/spells/source_relatedness/validator.go
@@ -36,9 +36,13 @@ func (v *Validator) Validate(_ context.Context, req contracts.TypedValidationReq
 	if err := spellshape.Validate(req.Value); err != nil {
 		return contracts.ValidationResult{Approved: true}, nil
 	}
+	resolver, err := shared.NewCitationResolver(req.Source)
+	if err != nil {
+		return contracts.ValidationResult{Approved: true}, nil
+	}
 	citedTexts := make([]string, len(req.Value.SpellCasts))
 	for spellIndex, spell := range req.Value.SpellCasts {
-		citedText, err := shared.CitedText(req.Source, spell.SourceRefs)
+		citedText, err := resolver.CitedText(spell.SourceRefs)
 		if err != nil {
 			return contracts.ValidationResult{Approved: true}, nil
 		}