diff --git a/docs/roadmap/implementation.md b/docs/roadmap/implementation.md
index f5ee3fc..7eb38db 100644
--- a/docs/roadmap/implementation.md
+++ b/docs/roadmap/implementation.md
@@ -371,7 +371,7 @@ Roadmap candidate 7. Owners: engine metadata, metadata cloning, inheritance hist
 Validate: `go test ./internal/engine -run 'Inheritance|Inherited|History|Metadata|Independent'`,
 engine race tests, and the everyday check.
 
-## Stage 15: Reuse frozen inspection mapping lookups
+## Stage 15: Reuse frozen inspection mapping lookups — Complete
 
 Roadmap candidate 7. Owners: publication, inspection, document/snapshot/history helpers.
 
diff --git a/internal/engine/document_lookup.go b/internal/engine/document_lookup.go
index 7036c2b..dec4d4e 100644
--- a/internal/engine/document_lookup.go
+++ b/internal/engine/document_lookup.go
@@ -7,7 +7,7 @@ type documentLookup struct {
 	byNode map[*document.Node]map[string]int
 }
 
-func buildDocumentLookup(root *document.Node) *documentLookup {
+func buildDocumentLookup(roots ...*document.Node) *documentLookup {
 	lookup := &documentLookup{byNode: make(map[*document.Node]map[string]int)}
 	visited := make(map[*document.Node]struct{})
 	var visit func(*document.Node)
@@ -35,7 +35,9 @@ func buildDocumentLookup(root *document.Node) *documentLookup {
 			}
 		}
 	}
-	visit(root)
+	for _, root := range roots {
+		visit(root)
+	}
 	return lookup
 }
 
diff --git a/internal/engine/explain.go b/internal/engine/explain.go
index 282a0cf..b350106 100644
--- a/internal/engine/explain.go
+++ b/internal/engine/explain.go
@@ -40,7 +40,7 @@ func (r *Inspection) Explain(path Path) (Explanation, bool) {
 	if r == nil || r.final == nil || r.baseline == nil || !r.metadata.hasHistoricalPath(path) {
 		return Explanation{}, false
 	}
-	explanation := Explanation{Path: path.clone(), Effective: valueSnapshot(r.final, path, r.secrets)}
+	explanation := Explanation{Path: path.clone(), Effective: valueSnapshotWithLookup(r.final, path, r.secrets, r.immutableLookup)}
 	if info, ok := r.metadata.Lookup(path); ok {
 		explanation.Origin = cloneOrigin(info.Origin)
 	}
@@ -53,7 +53,7 @@ func (r *Inspection) Explain(path Path) (Explanation, bool) {
 	}
 	replayIndex := new(mappingIndex)
 	for _, application := range r.applications {
-		operationPath, relevant := applicationOperationPath(application, path)
+		operationPath, relevant := applicationOperationPath(application, path, r.immutableLookup)
 		var before ValueSnapshot
 		if relevant {
 			before = valueSnapshot(working, path, r.secrets)
@@ -69,7 +69,7 @@ func (r *Inspection) Explain(path Path) (Explanation, bool) {
 		explanation.History = append(explanation.History, ValueChange{
 			Before: before,
 			After:  after,
-			Origin: historyApplicationOrigin(application, operationPath),
+			Origin: historyApplicationOrigin(application, operationPath, r.immutableLookup),
 		})
 	}
 	appendInheritanceExplanation(&explanation, &working, path, r.inheritance, r.secrets)
@@ -78,13 +78,13 @@ func (r *Inspection) Explain(path Path) (Explanation, bool) {
 	// decoding applies them to the final input tree. Show that reconciliation
 	// explicitly, including canonical scalar conversions, before domain changes.
 	replayed, _ := documentAtPath(working, path)
-	decoded, _ := documentAtPath(r.input, path)
+	decoded, _ := documentAtPathWithLookup(r.input, path, r.immutableLookup)
 	if !configurationValuesEqual(replayed, decoded) {
 		origin := cloneOrigin(r.inputOrigins[path.String()])
 		origin.Operation = ChangeDecoding
 		explanation.History = append(explanation.History, ValueChange{
 			Before:  valueSnapshot(working, path, r.secrets),
-			After:   valueSnapshot(r.input, path, r.secrets),
+			After:   valueSnapshotWithLookup(r.input, path, r.secrets, r.immutableLookup),
 			Origin:  origin,
 			Reasons: []string{"applied retained defaults and canonical typed decoding"},
 		})
diff --git a/internal/engine/explain_test.go b/internal/engine/explain_test.go
index 4cd9c27..5b80204 100644
--- a/internal/engine/explain_test.go
+++ b/internal/engine/explain_test.go
@@ -10,6 +10,7 @@ import (
 	"path/filepath"
 	"reflect"
 	"strings"
+	"sync"
 	"testing"
 
 	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
@@ -566,3 +567,49 @@ func TestExplanationReplayDescriptorsRemainDetachedAcrossQueries(t *testing.T) {
 	}
 	t.Fatalf("resolution change missing from repeated explanation: %#v", second.History)
 }
+
+func TestConcurrentReadOnlyInspectionQueries(t *testing.T) {
+	type config struct {
+		Group struct {
+			Value string `yaml:"value"`
+		} `yaml:"group"`
+	}
+	result, err := testLoad(Bytes("concurrent-inspection.yml", []byte("group: {value: input}\n")), Options[config]{
+		Definition: Definition[config]{Resolve: func(value *config, resolution *Resolution) error {
+			value.Group.Value = "resolved"
+			resolution.Record(Keys("group", "value"), ChangeNormalization, "normalized", Keys("group", "value"))
+			return nil
+		}},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	paths := []Path{Keys("group"), Keys("group", "value")}
+	var wait sync.WaitGroup
+	errors := make(chan string, 8)
+	for worker := 0; worker < cap(errors); worker++ {
+		wait.Add(1)
+		go func() {
+			defer wait.Done()
+			for iteration := 0; iteration < 8; iteration++ {
+				for _, path := range paths {
+					explanation, found := result.Explain(path)
+					if !found || !explanation.Effective.Present {
+						errors <- "missing effective explanation for " + path.String()
+						return
+					}
+					metadata := result.Metadata()
+					if _, found := metadata.Lookup(path); !found || len(metadata.History(path)) == 0 {
+						errors <- "missing metadata for " + path.String()
+						return
+					}
+				}
+			}
+		}()
+	}
+	wait.Wait()
+	close(errors)
+	for message := range errors {
+		t.Error(message)
+	}
+}
diff --git a/internal/engine/history.go b/internal/engine/history.go
index a72c526..546d407 100644
--- a/internal/engine/history.go
+++ b/internal/engine/history.go
@@ -65,7 +65,7 @@ func cloneHistoryApplications(values []historyApplication) []historyApplication
 	return cloned
 }
 
-func applicationOperationPath(application historyApplication, query Path) (Path, bool) {
+func applicationOperationPath(application historyApplication, query Path, lookup *documentLookup) (Path, bool) {
 	if !application.path.valid() || application.value == nil {
 		return Path{}, false
 	}
@@ -80,7 +80,7 @@ func applicationOperationPath(application historyApplication, query Path) (Path,
 	}
 	for length := 1; length <= len(query.segments); length++ {
 		prefix := Path{segments: clonePathSegments(query.segments[:length], 0)}
-		node, present := documentAtPath(application.value, prefix)
+		node, present := documentAtPathWithLookup(application.value, prefix, lookup)
 		if !present {
 			return Path{}, false
 		}
@@ -91,7 +91,7 @@ func applicationOperationPath(application historyApplication, query Path) (Path,
 	return Path{}, false
 }
 
-func historyApplicationOrigin(application historyApplication, operationPath Path) Origin {
+func historyApplicationOrigin(application historyApplication, operationPath Path, lookup *documentLookup) Origin {
 	if application.origin.Layer != "" {
 		return cloneOrigin(application.origin)
 	}
@@ -100,7 +100,7 @@ func historyApplicationOrigin(application historyApplication, operationPath Path
 	if !ok {
 		return origin
 	}
-	if node, present := documentAtPath(application.value, relative); present {
+	if node, present := documentAtPathWithLookup(application.value, relative, lookup); present {
 		origin.Locations = []Location{publicLocation(node.Location)}
 	}
 	return origin
diff --git a/internal/engine/load.go b/internal/engine/load.go
index 9c2fa0d..582a006 100644
--- a/internal/engine/load.go
+++ b/internal/engine/load.go
@@ -84,6 +84,7 @@ type Inspection struct {
 	input            *document.Node
 	inputOrigins     map[string]Origin
 	final            *document.Node
+	immutableLookup  *documentLookup
 	resolution       []resolutionSnapshot
 	resolutionReplay []resolutionSnapshot
 	applications     []historyApplication
diff --git a/internal/engine/load_result.go b/internal/engine/load_result.go
index 091a697..135452b 100644
--- a/internal/engine/load_result.go
+++ b/internal/engine/load_result.go
@@ -98,6 +98,11 @@ func publishLoadResult[T any](schema *schemaDescriptor, definition Definition[T]
 	final, applications, resolutionSnapshots := resolved.final, resolved.applications, resolved.snapshots
 	finalizeMetadataPaths(&metadata, final, applications, decoded.baseline, decoded.final)
 	secrets := classifySecretPaths(schema, definition.Secret, metadata, final, applications, decoded.baseline, decoded.final)
+	retainedTrees := make([]*document.Node, 0, len(applications)+2)
+	retainedTrees = append(retainedTrees, decoded.final, final)
+	for _, application := range applications {
+		retainedTrees = append(retainedTrees, application.value)
+	}
 	inspection := &Inspection{
 		metadata:         metadata,
 		sources:          cloneSourceInfos(accumulator.sources),
@@ -107,6 +112,7 @@ func publishLoadResult[T any](schema *schemaDescriptor, definition Definition[T]
 		input:            decoded.final,
 		inputOrigins:     cloneOriginIndex(decoded.origins),
 		final:            final,
+		immutableLookup:  buildDocumentLookup(retainedTrees...),
 		resolution:       resolutionSnapshots,
 		resolutionReplay: coalescedResolutionSnapshots(resolutionSnapshots),
 		applications:     applications,
diff --git a/internal/engine/resolution_index_test.go b/internal/engine/resolution_index_test.go
index a205e6e..701c1f8 100644
--- a/internal/engine/resolution_index_test.go
+++ b/internal/engine/resolution_index_test.go
@@ -102,7 +102,11 @@ func TestDocumentLookupMatchesPathScan(t *testing.T) {
 		{Key: "01", Value: &document.Node{Kind: document.String, Text: "leading zero key"}},
 		{Key: "items", Value: sequence},
 	}}
-	lookup := buildDocumentLookup(root)
+	applicationRoot := &document.Node{Kind: document.Mapping, Mapping: []document.Entry{
+		{Key: "shared", Value: sequence},
+		{Key: "application", Value: &document.Node{Kind: document.Mapping, Mapping: []document.Entry{{Key: "value", Value: &document.Node{Kind: document.String, Text: "application"}}}}},
+	}}
+	lookup := buildDocumentLookup(root, applicationRoot)
 	paths := []Path{
 		Path{},
 		Keys("0"),
@@ -123,6 +127,13 @@ func TestDocumentLookupMatchesPathScan(t *testing.T) {
 			t.Errorf("indexed lookup %s = (%p, %v), want (%p, %v)", path.String(), gotNode, gotFound, wantNode, wantFound)
 		}
 	}
+	for _, path := range []Path{Path{}, Keys("shared"), Keys("shared").Index(1).Key("name"), Keys("application", "value")} {
+		wantNode, wantFound := documentAtPath(applicationRoot, path)
+		gotNode, gotFound := documentAtPathWithLookup(applicationRoot, path, lookup)
+		if gotNode != wantNode || gotFound != wantFound {
+			t.Errorf("indexed application lookup %s = (%p, %v), want (%p, %v)", path.String(), gotNode, gotFound, wantNode, wantFound)
+		}
+	}
 }
 
 func TestApplyResolutionMetadataPreservesOverlappingDeltaOrder(t *testing.T) {
diff --git a/internal/engine/snapshot.go b/internal/engine/snapshot.go
index 7a97c9f..488b953 100644
--- a/internal/engine/snapshot.go
+++ b/internal/engine/snapshot.go
@@ -12,7 +12,11 @@ import (
 // Snapshot projection is the shared redaction boundary for effective YAML
 // and explanation values. It borrows frozen trees and returns a detached tree.
 func valueSnapshot(root *document.Node, path Path, secrets map[string]bool) ValueSnapshot {
-	node, present := documentAtPath(root, path)
+	return valueSnapshotWithLookup(root, path, secrets, nil)
+}
+
+func valueSnapshotWithLookup(root *document.Node, path Path, secrets map[string]bool, lookup *documentLookup) ValueSnapshot {
+	node, present := documentAtPathWithLookup(root, path, lookup)
 	if !present {
 		return ValueSnapshot{}
 	}