diff --git a/docs/roadmap/implementation.md b/docs/roadmap/implementation.md
index 9a8b33c..ad1b7e8 100644
--- a/docs/roadmap/implementation.md
+++ b/docs/roadmap/implementation.md
@@ -271,6 +271,13 @@ Scope: backend/profile field capture, normalization, and defaulting in
 Validation: owning tests demonstrate explicit zeros/nulls, backend completion,
 and recorded normalization at the correct list entries. No new readiness rule.
 
+Completion: backend and profile presence capture and resolution now use list
+indexes and mutate the effective slice elements while retaining full-ID state
+keys. Converted focused normalization, null/default, profile-presence, and
+same-ID replacement fixtures. Their execution remains deferred: the package
+still does not compile until the subsequent indexing, validation, and prompt
+list migrations. Formatting and `git diff --check` passed.
+
 ## Stage 5: Validate Final Records And Build Execution Indexes
 
 Scope: `validateEffective`, `indexedBackends`, `indexedProfiles`, and
diff --git a/internal/configuration/load.go b/internal/configuration/load.go
index aa9727d..9faba13 100644
--- a/internal/configuration/load.go
+++ b/internal/configuration/load.go
@@ -247,8 +247,8 @@ func load(main configkit.Input, underlays []configkit.Underlay) (*loaded, error)
 			Sensitive: secretProviderPath,
 			Resolve: func(config *document, resolution *configkit.Resolution) error {
 				for _, resources := range resourceSets(config) {
-					captureFields(resources.backends, resources.bases.backends, resources.namespace, backendFields, resolution, state.backends)
-					captureFields(resources.profiles, resources.bases.profiles, resources.namespace, profileFields, resolution, state.profiles)
+					captureFields(resources.backends, func(v backendConfig) string { return v.ID }, resources.bases.backends, resources.namespace, backendFields, resolution, state.backends)
+					captureFields(resources.profiles, func(v profileConfig) string { return v.ID }, resources.bases.profiles, resources.namespace, profileFields, resolution, state.profiles)
 					capturePromptMetadata(resources.prompts, resources.bases.prompts, resources.namespace, resolution, state.promptMetadata)
 					resolveBackends(resources.backends, resources.bases.backends, resolution)
 					resolveProfiles(resources.profiles, resources.bases.profiles, resolution)
@@ -351,11 +351,11 @@ func captureFieldState(path configkit.Path, resolution *configkit.Resolution) fi
 	}
 }
 
-func captureFields[T any](entries map[string]T, basePath configkit.Path, namespace string, fields []string, resolution *configkit.Resolution, destination map[string]map[string]fieldState) {
-	for id := range entries {
+func captureFields[T any](entries []T, identity func(T) string, basePath configkit.Path, namespace string, fields []string, resolution *configkit.Resolution, destination map[string]map[string]fieldState) {
+	for index, entry := range entries {
 		states := make(map[string]fieldState, len(fields))
 		for _, field := range fields {
-			info, exists := resolution.EntryInfo(basePath.Key(id).Key(field))
+			info, exists := resolution.EntryInfo(basePath.Index(index).Key(field))
 			switch {
 			case !exists || !info.Explicit:
 				states[field] = fieldAbsent
@@ -365,7 +365,7 @@ func captureFields[T any](entries map[string]T, basePath configkit.Path, namespa
 				states[field] = fieldValue
 			}
 		}
-		destination[indexedResourceID(namespace, id)] = states
+		destination[indexedResourceID(namespace, identity(entry))] = states
 	}
 }
 
@@ -386,10 +386,10 @@ func normalizeString(value **string, path configkit.Path, resolution *configkit.
 	return false
 }
 
-func resolveBackends(backends map[string]backendConfig, basePath configkit.Path, resolution *configkit.Resolution) {
-	for _, id := range sortedKeys(backends) {
-		backend := backends[id]
-		base := basePath.Key(id)
+func resolveBackends(backends []backendConfig, basePath configkit.Path, resolution *configkit.Resolution) {
+	for index := range backends {
+		backend := &backends[index]
+		base := basePath.Index(index)
 		if backend.Endpoint != nil {
 			endpoint, err := domain.NormalizeOpenAICompatibleBaseEndpoint(*backend.Endpoint)
 			if err != nil {
@@ -424,7 +424,6 @@ func resolveBackends(backends map[string]backendConfig, basePath configkit.Path,
 				configkit.Default(resolution, base.Key("queue_capacity"), &backend.QueueCapacity, &capacity, "select default queue capacity")
 			}
 		}
-		backends[id] = backend
 	}
 }
 
@@ -443,10 +442,10 @@ func normalizeDiagnosticEndpoint(value **string, path configkit.Path, resolution
 	normalizeString(value, path, resolution, normalized)
 }
 
-func resolveProfiles(profiles map[string]profileConfig, basePath configkit.Path, resolution *configkit.Resolution) {
-	for _, id := range sortedKeys(profiles) {
-		profile := profiles[id]
-		base := basePath.Key(id)
+func resolveProfiles(profiles []profileConfig, basePath configkit.Path, resolution *configkit.Resolution) {
+	for index := range profiles {
+		profile := &profiles[index]
+		base := basePath.Index(index)
 		if profile.Endpoint != nil && *profile.Endpoint != "" {
 			endpoint, err := domain.NormalizeOpenAICompatibleBaseEndpoint(*profile.Endpoint)
 			if err != nil {
@@ -467,7 +466,6 @@ func resolveProfiles(profiles map[string]profileConfig, basePath configkit.Path,
 				normalizeString(field.value, base.Key(field.name), resolution, strings.TrimSpace(**field.value))
 			}
 		}
-		profiles[id] = profile
 	}
 }
 
diff --git a/internal/configuration/load_test.go b/internal/configuration/load_test.go
index 382a58c..e7e3edb 100644
--- a/internal/configuration/load_test.go
+++ b/internal/configuration/load_test.go
@@ -230,14 +230,14 @@ func TestLoadRejectsInvalidCollectionAndResourceKeys(t *testing.T) {
 }
 
 func TestLoadRecordsBackendNormalizationAndNullDefault(t *testing.T) {
-	loaded, err := load(mapping("backend", map[string]any{"backends": map[string]any{
-		"local": map[string]any{"endpoint": " HTTP://localhost:8080/v1 ", "api_key_env": " TOKEN_NAME ",
+	loaded, err := load(mapping("backend", map[string]any{"backends": []any{
+		map[string]any{"id": "local", "endpoint": " HTTP://localhost:8080/v1 ", "api_key_env": " TOKEN_NAME ",
 			"concurrency_limit": 2, "queue_capacity": nil},
 	}}), nil)
 	if err != nil {
 		t.Fatal(err)
 	}
-	backend := loaded.result.Config.Backends["local"]
+	backend := loaded.result.Config.Backends[0]
 	if backend.Endpoint == nil || *backend.Endpoint != "http://localhost:8080/v1" ||
 		backend.APIKeyEnv == nil || *backend.APIKeyEnv != "TOKEN_NAME" ||
 		backend.QueueCapacity == nil || *backend.QueueCapacity != 1024 {
@@ -246,6 +246,10 @@ func TestLoadRecordsBackendNormalizationAndNullDefault(t *testing.T) {
 	if loaded.backends["local"]["queue_capacity"] != fieldNull {
 		t.Fatalf("explicit null was not retained: %+v", loaded.backends["local"])
 	}
+	field, found := loaded.result.Metadata().Lookup(configkit.Keys("backends").Index(0).Key("endpoint"))
+	if !found || field.Origin.Operation != configkit.ChangeNormalization {
+		t.Fatalf("endpoint normalization was not recorded at the list entry: %+v", field)
+	}
 }
 
 func TestLoadBackendSmokeTestsOmissionAndNull(t *testing.T) {
@@ -402,15 +406,35 @@ func TestLoadRejectsInvalidFinalBackendSmokeTests(t *testing.T) {
 }
 
 func TestLoadDefaultsAbsentQueueCapacity(t *testing.T) {
-	loaded, err := load(mapping("backend", map[string]any{"backends": map[string]any{
-		"local": map[string]any{"endpoint": "http://localhost:8080/v1", "concurrency_limit": 1},
+	underlay := mapping("defaults", map[string]any{"backends": []any{
+		map[string]any{"id": "local", "endpoint": "http://localhost:8080/v1", "api_key_env": "OLD_KEY"},
+	}})
+	loaded, err := load(mapping("backend", map[string]any{"backends": []any{
+		map[string]any{"id": "local", "endpoint": "http://localhost:8080/v1", "concurrency_limit": 1},
+	}}), []configkit.Underlay{{Inputs: []configkit.Input{underlay}}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	backend := loaded.result.Config.Backends[0]
+	if backend.APIKeyEnv != nil || backend.QueueCapacity == nil || *backend.QueueCapacity != 1024 || loaded.backends["local"]["queue_capacity"] != fieldAbsent {
+		t.Fatalf("absent queue capacity did not receive its default: %+v", backend)
+	}
+}
+
+func TestLoadCapturesProfilePresence(t *testing.T) {
+	loaded, err := load(mapping("profile", map[string]any{"profiles": []any{
+		map[string]any{"id": "local", "temperature": 0, "top_p": nil, "api_key_required": false},
 	}}), nil)
 	if err != nil {
 		t.Fatal(err)
 	}
-	backend := loaded.result.Config.Backends["local"]
-	if backend.QueueCapacity == nil || *backend.QueueCapacity != 1024 || loaded.backends["local"]["queue_capacity"] != fieldAbsent {
-		t.Fatalf("absent queue capacity did not receive its default: %+v", backend)
+	profile := loaded.result.Config.Profiles[0]
+	if profile.Temperature == nil || *profile.Temperature != 0 || profile.TopP != nil || profile.APIKeyRequired == nil || *profile.APIKeyRequired {
+		t.Fatalf("profile values were not preserved: %+v", profile)
+	}
+	fields := loaded.profiles["local"]
+	if fields["temperature"] != fieldValue || fields["top_p"] != fieldNull || fields["api_key_required"] != fieldValue || fields["model"] != fieldAbsent {
+		t.Fatalf("profile presence was not preserved: %+v", fields)
 	}
 }