diff --git a/docs/roadmap/implementation.md b/docs/roadmap/implementation.md
index 56171dc..014fb93 100644
--- a/docs/roadmap/implementation.md
+++ b/docs/roadmap/implementation.md
@@ -414,7 +414,7 @@ Roadmap candidate 8. Owner: engine `inheritance_origin.go`.
 Validate: `go test ./internal/engine -run 'Inheritance|Inherited|Metadata|Provenance|History'`
 and the everyday check. Complex contributor-trace equality stays unchanged.
 
-## Stage 17: Index simple resolution and origin membership
+## Stage 17: Index simple resolution and origin membership — Complete
 
 Roadmap candidate 8. Owners: engine `resolution.go` and `load_metadata.go`.
 
diff --git a/internal/engine/inheritance_origin_test.go b/internal/engine/inheritance_origin_test.go
index 2f872c4..bec8a98 100644
--- a/internal/engine/inheritance_origin_test.go
+++ b/internal/engine/inheritance_origin_test.go
@@ -87,6 +87,51 @@ func TestInheritedOriginsKeepSourcePathsPresenceAndIndependentReplacement(t *tes
 	}
 }
 
+func TestOriginMembershipPreservesLocationAndSourceCoverageRules(t *testing.T) {
+	location := Location{SourceID: "source", Line: 4, Column: 2}
+	otherCoordinates := location
+	otherCoordinates.Line++
+
+	container := Origin{
+		Layer:     LayerOverlay,
+		Operation: ChangeNormalization,
+		Locations: []Location{location},
+	}
+	if !originContainedBy(container, container) {
+		t.Fatal("identical location evidence was not contained")
+	}
+	coordinateDifference := container
+	coordinateDifference.Locations = []Location{otherCoordinates}
+	if originContainedBy(coordinateDifference, container) {
+		t.Fatal("location containment ignored differing coordinates")
+	}
+
+	parent := Keys("parent")
+	child := parent.Key("child")
+	change := Change{Path: parent, Origin: container}
+	descendantOrigin := Origin{
+		Layer:     container.Layer,
+		Operation: container.Operation,
+		Locations: []Location{otherCoordinates},
+	}
+	if !originRepresentedByChange(child, descendantOrigin, change) {
+		t.Fatal("descendant source coverage rejected matching SourceID with different coordinates")
+	}
+	descendantOrigin.Locations[0].SourceID = "another-source"
+	if originRepresentedByChange(child, descendantOrigin, change) {
+		t.Fatal("descendant source coverage accepted an unrecorded SourceID")
+	}
+
+	withContributor := container
+	withContributor.contributors = []inheritanceContributor{{source: parent, location: location}}
+	if originContainedBy(withContributor, container) {
+		t.Fatal("exact location containment ignored the contributor-empty mismatch")
+	}
+	if !originRepresentedByChange(child, withContributor, change) {
+		t.Fatal("descendant source coverage was conflated with contributor containment")
+	}
+}
+
 func TestProjectedInheritanceStepsMatchScanAndRetainOwnership(t *testing.T) {
 	sourcePath := Keys("source", "a/b", "01")
 	firstLocations := []Location{{SourceID: "first;:source", Line: -1, Column: 2}}
diff --git a/internal/engine/load_metadata.go b/internal/engine/load_metadata.go
index 2a8bf8a..8bc936c 100644
--- a/internal/engine/load_metadata.go
+++ b/internal/engine/load_metadata.go
@@ -157,15 +157,12 @@ func originRepresentedByChange(path Path, origin Origin, change Change) bool {
 	// A subtree replacement already records its descendants' contributions.
 	// Their coordinates differ from the container's, but their sources must be
 	// covered by the operation; matching only the precedence role is insufficient.
+	recordedSources := make(map[string]struct{}, len(change.Origin.Locations))
+	for _, recorded := range change.Origin.Locations {
+		recordedSources[recorded.SourceID] = struct{}{}
+	}
 	for _, location := range origin.Locations {
-		found := false
-		for _, recorded := range change.Origin.Locations {
-			if location.SourceID == recorded.SourceID {
-				found = true
-				break
-			}
-		}
-		if !found {
+		if _, found := recordedSources[location.SourceID]; !found {
 			return false
 		}
 	}
@@ -189,15 +186,12 @@ func originContainedBy(candidate, container Origin) bool {
 	if candidate.Layer != container.Layer || candidate.Operation != container.Operation {
 		return false
 	}
+	availableLocations := make(map[Location]struct{}, len(container.Locations))
+	for _, location := range container.Locations {
+		availableLocations[location] = struct{}{}
+	}
 	for _, location := range candidate.Locations {
-		found := false
-		for _, available := range container.Locations {
-			if location == available {
-				found = true
-				break
-			}
-		}
-		if !found {
+		if _, found := availableLocations[location]; !found {
 			return false
 		}
 	}
diff --git a/internal/engine/resolution.go b/internal/engine/resolution.go
index 9075916..b11c520 100644
--- a/internal/engine/resolution.go
+++ b/internal/engine/resolution.go
@@ -26,6 +26,37 @@ type resolutionRecord struct {
 	reasons        []string
 	dependencies   []Path
 	helperExpected *document.Node
+	reasonSet      map[string]struct{}
+	dependencySet  map[string]struct{}
+}
+
+func (record *resolutionRecord) addReason(reason string) {
+	if record.reasonSet == nil {
+		record.reasonSet = make(map[string]struct{}, len(record.reasons)+1)
+		for _, existing := range record.reasons {
+			record.reasonSet[existing] = struct{}{}
+		}
+	}
+	if _, found := record.reasonSet[reason]; found {
+		return
+	}
+	record.reasonSet[reason] = struct{}{}
+	record.reasons = append(record.reasons, reason)
+}
+
+func (record *resolutionRecord) addDependency(path Path) {
+	pointer := path.String()
+	if record.dependencySet == nil {
+		record.dependencySet = make(map[string]struct{}, len(record.dependencies)+1)
+		for _, existing := range record.dependencies {
+			record.dependencySet[existing.String()] = struct{}{}
+		}
+	}
+	if _, found := record.dependencySet[pointer]; found {
+		return
+	}
+	record.dependencySet[pointer] = struct{}{}
+	record.dependencies = append(record.dependencies, path.clone())
 }
 
 type resolutionSnapshot struct {
@@ -207,9 +238,9 @@ func (state *resolutionState) addRecord(path Path, kind ChangeKind, reason strin
 	if kind == ChangeNormalization {
 		record.kind = ChangeNormalization
 	}
-	record.reasons = appendUniqueString(record.reasons, reason)
+	record.addReason(reason)
 	for _, dependency := range dependencies {
-		record.dependencies = appendUniquePath(record.dependencies, dependency)
+		record.addDependency(dependency)
 	}
 	if expected != nil {
 		record.helperExpected = document.Clone(expected)
diff --git a/internal/engine/resolution_test.go b/internal/engine/resolution_test.go
index 19bef35..bb60576 100644
--- a/internal/engine/resolution_test.go
+++ b/internal/engine/resolution_test.go
@@ -122,6 +122,11 @@ func TestResolutionPreservesExplicitNullAndZeroWhileReplacingAbsentBaseline(t *t
 func TestResolutionCoalescesEqualAndRepeatedHelperIntent(t *testing.T) {
 	t.Parallel()
 
+	parsedOther, err := ParsePath("/other")
+	if err != nil {
+		t.Fatal(err)
+	}
+
 	type config struct {
 		Value int `yaml:"value"`
 		Other int `yaml:"other"`
@@ -130,8 +135,9 @@ func TestResolutionCoalescesEqualAndRepeatedHelperIntent(t *testing.T) {
 		Defaults: func() config { return config{Value: 5} },
 		Resolve: func(configuration *config, resolution *Resolution) error {
 			Default(resolution, Keys("value"), &configuration.Value, 5, "equal derived intent", Keys("other"))
-			Default(resolution, Keys("value"), &configuration.Value, 7, "updated derived intent", Keys("other"))
+			Default(resolution, Keys("value"), &configuration.Value, 7, "updated derived intent", parsedOther)
 			Normalize(resolution, Keys("value"), &configuration.Value, 7, "canonicalized value", Keys("other"))
+			Normalize(resolution, Keys("value"), &configuration.Value, 7, "updated derived intent", parsedOther)
 			return nil
 		},
 	}})