diff --git a/configuration_inspection_contract_test.go b/configuration_inspection_contract_test.go
index 774ff09..302e8f2 100644
--- a/configuration_inspection_contract_test.go
+++ b/configuration_inspection_contract_test.go
@@ -23,13 +23,19 @@ func TestConfigurationInspectionReportsLiteralKeysAndRedactedHistory(t *testing.
 					"endpoint": "https://example.invalid/v1", "api_key_env": "OPTIONAL_KEY",
 					"extra_params": map[string]any{"token": "private-sentinel", "visible": "public-value"},
 				}},
-				"profiles": map[string]any{
-					"base.v1":    map[string]any{"backend": "local", "model": "default-model"},
-					"literal/id": map[string]any{"extends": "base.v1"},
-				},
+				"collections": map[string]any{"literal": map[string]any{
+					"backends": map[string]any{"local": map[string]any{
+						"endpoint":     "https://example.invalid/v1",
+						"extra_params": map[string]any{"token": "namespaced-private-sentinel"},
+					}},
+					"profiles": map[string]any{
+						"base.v1": map[string]any{"backend": "local", "model": "default-model"},
+						"id":      map[string]any{"extends": "base.v1"},
+					},
+				}},
 			})}}},
 			{Inputs: []configkit.Input{{Source: configkit.Mapping("operator", map[string]any{
-				"profiles": map[string]any{"base.v1": map[string]any{"model": "operator-model"}},
+				"collections": map[string]any{"literal": map[string]any{"profiles": map[string]any{"base.v1": map[string]any{"model": "operator-model"}}}},
 			})}}},
 		},
 	}})
@@ -40,17 +46,17 @@ func TestConfigurationInspectionReportsLiteralKeysAndRedactedHistory(t *testing.
 	if err != nil {
 		t.Fatalf("inspect configuration: %v", err)
 	}
-	modelPath := configkit.Keys("profiles", "base.v1", "model")
+	modelPath := configkit.Keys("collections", "literal", "profiles", "base.v1", "model")
 	model, found := view.Explain(modelPath)
 	if !found || !strings.Contains(model.Effective.YAML, "operator-model") || len(model.History) < 2 {
 		t.Fatalf("layered model explanation = (%+v, %t)", model, found)
 	}
-	inheritedPath := configkit.Keys("profiles", "literal/id", "model")
+	inheritedPath := configkit.Keys("collections", "literal", "profiles", "id", "model")
 	inherited, found := view.Explain(inheritedPath)
 	if !found || !strings.Contains(inherited.Effective.YAML, "operator-model") || len(inherited.History) == 0 || !view.Metadata().IsExplicit(inheritedPath) {
 		t.Fatalf("literal-key inheritance explanation = (%+v, %t)", inherited, found)
 	}
-	if inheritedPath.String() != "/profiles/literal~1id/model" {
+	if inheritedPath.String() != "/collections/literal/profiles/id/model" {
 		t.Fatalf("literal-key path = %q", inheritedPath)
 	}
 	secretPath := configkit.Keys("backends", "local", "extra_params", "token")
@@ -58,6 +64,11 @@ func TestConfigurationInspectionReportsLiteralKeysAndRedactedHistory(t *testing.
 	if !found || !secret.Effective.Redacted || strings.Contains(secret.Effective.YAML, "private-sentinel") {
 		t.Fatalf("credential-shaped provider value was not redacted: (%+v, %t)", secret, found)
 	}
+	namespacedSecretPath := configkit.Keys("collections", "literal", "backends", "local", "extra_params", "token")
+	namespacedSecret, found := view.Explain(namespacedSecretPath)
+	if !found || !namespacedSecret.Effective.Redacted || strings.Contains(namespacedSecret.Effective.YAML, "namespaced-private-sentinel") {
+		t.Fatalf("namespaced provider value was not redacted: (%+v, %t)", namespacedSecret, found)
+	}
 	var effective bytes.Buffer
 	if err := view.WriteEffective(&effective); err != nil {
 		t.Fatalf("write effective configuration: %v", err)
@@ -66,7 +77,7 @@ func TestConfigurationInspectionReportsLiteralKeysAndRedactedHistory(t *testing.
 		t.Fatalf("unexpected effective report: %s", effective.String())
 	}
 	var explanation bytes.Buffer
-	if err := view.WriteExplanation(&explanation, secretPath); err != nil || strings.Contains(explanation.String(), "private-sentinel") {
+	if err := view.WriteExplanation(&explanation, namespacedSecretPath); err != nil || strings.Contains(explanation.String(), "namespaced-private-sentinel") {
 		t.Fatalf("secret explanation = (%q, %v)", explanation.String(), err)
 	}
 
diff --git a/docs/roadmap/implementation.md b/docs/roadmap/implementation.md
index 514cbcf..25815b3 100644
--- a/docs/roadmap/implementation.md
+++ b/docs/roadmap/implementation.md
@@ -508,6 +508,14 @@ release metadata, sibling inheritance, headerless collection fragments, resource
 named `version` in nested mappings, and header/declaration distinctions.
 Run `GOWORK=off go test ./internal/configuration .`.
 
+Completion: final root and collection resources are interpreted from their
+effective ConfigKit paths and indexed under full runtime IDs without re-keying
+the retained result. Collection namespaces and local keys are validated;
+collection release labels, sibling inheritance, inherited relative content,
+presence/null handling, and namespaced secret redaction are covered. Capacity
+and profile snapshots use full backend identities. Validation passed:
+`GOWORK=off go test ./...`, `GOWORK=off go vet ./...`, and `git diff --check`.
+
 ## Stage 9: Make Application Tests Independent Of Bundled Catalogs
 
 Scope: owned fixtures and examples that currently assume automatic provider data.
diff --git a/internal/configuration/inspection.go b/internal/configuration/inspection.go
index 80148cd..dfd0c18 100644
--- a/internal/configuration/inspection.go
+++ b/internal/configuration/inspection.go
@@ -66,6 +66,11 @@ func secretProviderPath(path configkit.Path) bool {
 }
 
 func providerExtraParamsPath(parts []string) bool {
-	return len(parts) >= 4 && parts[1] != "" &&
-		(parts[0] == "backends" || parts[0] == "profiles") && parts[2] == "extra_params"
+	if len(parts) >= 4 && parts[1] != "" &&
+		(parts[0] == "backends" || parts[0] == "profiles") && parts[2] == "extra_params" {
+		return true
+	}
+	return len(parts) >= 6 && parts[0] == "collections" && parts[1] != "" &&
+		(parts[2] == "backends" || parts[2] == "profiles") &&
+		parts[3] != "" && parts[4] == "extra_params"
 }
diff --git a/internal/configuration/inspection_test.go b/internal/configuration/inspection_test.go
index b872a12..6d00588 100644
--- a/internal/configuration/inspection_test.go
+++ b/internal/configuration/inspection_test.go
@@ -14,8 +14,11 @@ func TestSecretProviderPathRecognizesResourceExtraParams(t *testing.T) {
 	}{
 		{name: "backend nested secret", path: configkit.Keys("backends", "provider", "extra_params", "nested", "Token"), want: true},
 		{name: "profile nested secret", path: configkit.Keys("profiles", "assistant", "extra_params", "authorization"), want: true},
+		{name: "collection backend nested secret", path: configkit.Keys("collections", "provider", "backends", "default", "extra_params", "nested", "Token"), want: true},
+		{name: "collection profile secret", path: configkit.Keys("collections", "assistant", "profiles", "model", "extra_params", "authorization"), want: true},
 		{name: "unrelated nested mapping", path: configkit.Keys("application", "backends", "provider", "extra_params", "token"), want: false},
 		{name: "extra params outside resource map", path: configkit.Keys("backends", "provider", "options", "extra_params", "token"), want: false},
+		{name: "collection extra params outside resource map", path: configkit.Keys("collections", "provider", "settings", "backends", "default", "extra_params", "token"), want: false},
 		{name: "missing resource key", path: configkit.Keys("backends", "", "extra_params", "token"), want: false},
 		{name: "ordinary provider value", path: configkit.Keys("profiles", "assistant", "extra_params", "provider", "mode"), want: false},
 	}
diff --git a/internal/configuration/listing_test.go b/internal/configuration/listing_test.go
index 3e5cf7b..5fd1631 100644
--- a/internal/configuration/listing_test.go
+++ b/internal/configuration/listing_test.go
@@ -15,16 +15,11 @@ func TestLoadedListsSortedEffectiveIdentities(t *testing.T) {
 		"backends": map[string]any{
 			"local": map[string]any{"endpoint": "http://localhost:8080/v1"},
 		},
-		"profiles": map[string]any{
-			"z/profile":       map[string]any{"backend": "local", "model": "z-model"},
-			"partial/profile": map[string]any{"backend": "local"},
-			"a/profile":       map[string]any{"backend": "local", "model": "a-model"},
-			" z/profile ":     map[string]any{"backend": "local", "model": "spaced-model"},
-		},
-		"prompts": map[string]any{
-			"z/prompt":   listingPromptDefinition(),
-			"a/prompt":   listingPromptDefinition(),
-			" z/prompt ": listingPromptDefinition(),
+		"collections": map[string]any{
+			"z":       map[string]any{"profiles": map[string]any{"profile": map[string]any{"backend": "local", "model": "z-model"}}, "prompts": map[string]any{"prompt": listingPromptDefinition()}},
+			"partial": map[string]any{"profiles": map[string]any{"profile": map[string]any{"backend": "local"}}},
+			"a":       map[string]any{"profiles": map[string]any{"profile": map[string]any{"backend": "local", "model": "a-model"}}, "prompts": map[string]any{"prompt": listingPromptDefinition()}},
+			" z":      map[string]any{"profiles": map[string]any{"profile ": map[string]any{"backend": "local", "model": "spaced-model"}}, "prompts": map[string]any{"prompt ": listingPromptDefinition()}},
 		},
 	}), nil)
 	if err != nil {
diff --git a/internal/configuration/load.go b/internal/configuration/load.go
index 1e60149..a95a7bb 100644
--- a/internal/configuration/load.go
+++ b/internal/configuration/load.go
@@ -17,10 +17,18 @@ import (
 )
 
 type document struct {
-	Version  *string                  `yaml:"version"`
-	Backends map[string]backendConfig `yaml:"backends"`
-	Profiles map[string]profileConfig `yaml:"profiles"`
-	Prompts  map[string]promptConfig  `yaml:"prompts"`
+	Version     *string                     `yaml:"version"`
+	Backends    map[string]backendConfig    `yaml:"backends"`
+	Profiles    map[string]profileConfig    `yaml:"profiles"`
+	Prompts     map[string]promptConfig     `yaml:"prompts"`
+	Collections map[string]collectionConfig `yaml:"collections"`
+}
+
+type collectionConfig struct {
+	ReleaseVersion *string                  `yaml:"release_version"`
+	Backends       map[string]backendConfig `yaml:"backends"`
+	Profiles       map[string]profileConfig `yaml:"profiles"`
+	Prompts        map[string]promptConfig  `yaml:"prompts"`
 }
 
 type backendConfig struct {
@@ -126,6 +134,15 @@ type resourceBases struct {
 	prompts  configkit.Path
 }
 
+type resourceSet struct {
+	isCollection bool
+	namespace    string
+	bases        resourceBases
+	backends     map[string]backendConfig
+	profiles     map[string]profileConfig
+	prompts      map[string]promptConfig
+}
+
 func rootResourceBases() resourceBases {
 	return resourceBases{
 		backends: configkit.Keys("backends"),
@@ -134,6 +151,61 @@ func rootResourceBases() resourceBases {
 	}
 }
 
+func resourceSets(config *document) []resourceSet {
+	sets := make([]resourceSet, 0, len(config.Collections)+1)
+	sets = append(sets, resourceSet{
+		bases: rootResourceBases(), backends: config.Backends, profiles: config.Profiles, prompts: config.Prompts,
+	})
+	for _, namespace := range sortedKeys(config.Collections) {
+		collection := config.Collections[namespace]
+		base := configkit.Keys("collections", namespace)
+		sets = append(sets, resourceSet{
+			isCollection: true,
+			namespace:    namespace,
+			bases: resourceBases{
+				backends: base.Key("backends"),
+				profiles: base.Key("profiles"),
+				prompts:  base.Key("prompts"),
+			},
+			backends: collection.Backends,
+			profiles: collection.Profiles,
+			prompts:  collection.Prompts,
+		})
+	}
+	return sets
+}
+
+func indexedResourceID(namespace, localKey string) string {
+	qualified, valid := domain.QualifyLocalResourceID(namespace, localKey)
+	if valid {
+		return qualified
+	}
+	if namespace == "" {
+		return localKey
+	}
+	return namespace + "/" + localKey
+}
+
+func indexedBackends(config *document) map[string]backendConfig {
+	backends := make(map[string]backendConfig)
+	for _, resources := range resourceSets(config) {
+		for localKey, definition := range resources.backends {
+			backends[indexedResourceID(resources.namespace, localKey)] = definition
+		}
+	}
+	return backends
+}
+
+func indexedProfiles(config *document) map[string]profileConfig {
+	profiles := make(map[string]profileConfig)
+	for _, resources := range resourceSets(config) {
+		for localKey, definition := range resources.profiles {
+			profiles[indexedResourceID(resources.namespace, localKey)] = definition
+		}
+	}
+	return profiles
+}
+
 var envName = regexp.MustCompile(`^[A-Za-z_][A-Za-z0-9_]*$`)
 
 var backendFields = []string{"endpoint", "api_key_env", "concurrency_limit", "queue_capacity", "extra_params", "smoke_tests"}
@@ -146,7 +218,6 @@ func Load(main configkit.Input, underlays []configkit.Underlay) (*loaded, error)
 
 // load performs one ConfigKit lifecycle over the selected source tiers.
 func load(main configkit.Input, underlays []configkit.Underlay) (*loaded, error) {
-	bases := rootResourceBases()
 	state := &loaded{
 		backends:       make(map[string]map[string]fieldState),
 		profiles:       make(map[string]map[string]fieldState),
@@ -162,16 +233,18 @@ func load(main configkit.Input, underlays []configkit.Underlay) (*loaded, error)
 			},
 			Secret: secretProviderPath,
 			Resolve: func(config *document, resolution *configkit.Resolution) error {
-				captureFields(config.Backends, bases.backends, backendFields, resolution, state.backends)
-				captureFields(config.Profiles, bases.profiles, profileFields, resolution, state.profiles)
-				capturePromptMetadata(config.Prompts, bases.prompts, resolution, state.promptMetadata)
-				resolveBackends(config.Backends, bases.backends, resolution)
-				resolveProfiles(config.Profiles, bases.profiles, resolution)
-				resolvePrompts(config.Prompts, bases.prompts, resolution)
+				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)
+					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)
+					resolvePrompts(resources.prompts, resources.bases.prompts, resolution)
+				}
 				return nil
 			},
 			Validate: func(config *document, validation *configkit.Validation) {
-				validateEffective(config, bases, validation)
+				validateEffective(config, validation)
 			},
 		},
 	})
@@ -179,8 +252,10 @@ func load(main configkit.Input, underlays []configkit.Underlay) (*loaded, error)
 		return nil, fmt.Errorf("load configuration: %w", err)
 	}
 	state.result = result
-	if err := state.materializePrompts(result.Config.Prompts, bases.prompts); err != nil {
-		return nil, fmt.Errorf("load configuration: %w", err)
+	for _, resources := range resourceSets(&result.Config) {
+		if err := state.materializePrompts(resources.prompts, resources.bases.prompts, resources.namespace); err != nil {
+			return nil, fmt.Errorf("load configuration: %w", err)
+		}
 	}
 	if err := state.buildExecutionProfiles(); err != nil {
 		return nil, fmt.Errorf("load configuration: %w", err)
@@ -207,7 +282,7 @@ type promptInputPresence struct {
 	description fieldState
 }
 
-func capturePromptMetadata(prompts map[string]promptConfig, basePath configkit.Path, resolution *configkit.Resolution, destination map[string][]promptInputPresence) {
+func capturePromptMetadata(prompts map[string]promptConfig, basePath configkit.Path, namespace string, resolution *configkit.Resolution, destination map[string][]promptInputPresence) {
 	for _, id := range sortedKeys(prompts) {
 		inputs := prompts[id].Inputs
 		states := make([]promptInputPresence, len(inputs))
@@ -219,7 +294,7 @@ func capturePromptMetadata(prompts map[string]promptConfig, basePath configkit.P
 				description: captureFieldState(path.Key("description"), resolution),
 			}
 		}
-		destination[id] = states
+		destination[indexedResourceID(namespace, id)] = states
 	}
 }
 
@@ -235,7 +310,7 @@ func captureFieldState(path configkit.Path, resolution *configkit.Resolution) fi
 	}
 }
 
-func captureFields[T any](entries map[string]T, basePath configkit.Path, fields []string, resolution *configkit.Resolution, destination map[string]map[string]fieldState) {
+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 {
 		states := make(map[string]fieldState, len(fields))
 		for _, field := range fields {
@@ -249,7 +324,7 @@ func captureFields[T any](entries map[string]T, basePath configkit.Path, fields
 				states[field] = fieldValue
 			}
 		}
-		destination[id] = states
+		destination[indexedResourceID(namespace, id)] = states
 	}
 }
 
@@ -355,83 +430,111 @@ func resolveProfiles(profiles map[string]profileConfig, basePath configkit.Path,
 	}
 }
 
-func validateEffective(config *document, bases resourceBases, validation *configkit.Validation) {
-	for _, id := range sortedKeys(config.Backends) {
-		backend := config.Backends[id]
-		base := bases.backends.Key(id)
-		if strings.TrimSpace(id) == "" {
-			validation.Error(base, "backend ID must not be blank")
+func validateEffective(config *document, validation *configkit.Validation) {
+	sets := resourceSets(config)
+	backendIDs := make(map[string]struct{})
+	for _, resources := range sets {
+		if resources.isCollection && !domain.IsValidResourceNamespace(resources.namespace) {
+			validation.Error(configkit.Keys("collections", resources.namespace), "collection namespace must be nonblank and contain no slash")
 		}
-		if backend.Endpoint == nil || *backend.Endpoint == "" {
-			validation.Error(base.Key("endpoint"), "endpoint is required")
+		for localKey := range resources.backends {
+			backendIDs[indexedResourceID(resources.namespace, localKey)] = struct{}{}
 		}
-		if backend.APIKeyEnv != nil && *backend.APIKeyEnv != "" && !envName.MatchString(*backend.APIKeyEnv) {
-			validation.Error(base.Key("api_key_env"), "environment variable name is invalid")
-		}
-		if backend.ConcurrencyLimit != nil && *backend.ConcurrencyLimit < 0 {
-			validation.Error(base.Key("concurrency_limit"), "concurrency limit must not be negative")
-		}
-		if backend.QueueCapacity != nil {
-			if *backend.QueueCapacity < 0 {
-				validation.Error(base.Key("queue_capacity"), "queue capacity must not be negative")
+	}
+	for _, resources := range sets {
+		for _, id := range sortedKeys(resources.backends) {
+			backend := resources.backends[id]
+			base := resources.bases.backends.Key(id)
+			if !domain.IsValidLocalResourceKey(id) {
+				validation.Error(base, "backend key must be a nonblank local key without a slash")
 			}
-			if backend.ConcurrencyLimit == nil || *backend.ConcurrencyLimit <= 0 {
-				validation.Error(base.Key("queue_capacity"), "queue capacity requires a positive concurrency limit")
-			} else if *backend.QueueCapacity > int(^uint(0)>>1)-*backend.ConcurrencyLimit {
-				validation.Error(base.Key("queue_capacity"), "total capacity overflows int")
+			if backend.Endpoint == nil || *backend.Endpoint == "" {
+				validation.Error(base.Key("endpoint"), "endpoint is required")
 			}
-		}
-		validateExtraParams(backend.ExtraParams, base.Key("extra_params"), true, validation)
-		if smokeTests := backend.SmokeTests; smokeTests != nil {
-			smokePath := base.Key("smoke_tests")
-			if smokeTests.DefaultProfile != nil && strings.TrimSpace(*smokeTests.DefaultProfile) == "" {
-				validation.Error(smokePath.Key("default_profile"), "default profile must not be blank")
+			if backend.APIKeyEnv != nil && *backend.APIKeyEnv != "" && !envName.MatchString(*backend.APIKeyEnv) {
+				validation.Error(base.Key("api_key_env"), "environment variable name is invalid")
 			}
-			if authentication := smokeTests.Authentication; authentication != nil {
-				kindPath := smokePath.Key("authentication").Key("kind")
-				if authentication.Kind == nil {
-					validation.Error(kindPath, "authentication kind is required")
-				} else if *authentication.Kind != "none" && *authentication.Kind != "openrouter_key" {
-					validation.Error(kindPath, "authentication kind must be none or openrouter_key")
+			if backend.ConcurrencyLimit != nil && *backend.ConcurrencyLimit < 0 {
+				validation.Error(base.Key("concurrency_limit"), "concurrency limit must not be negative")
+			}
+			if backend.QueueCapacity != nil {
+				if *backend.QueueCapacity < 0 {
+					validation.Error(base.Key("queue_capacity"), "queue capacity must not be negative")
+				}
+				if backend.ConcurrencyLimit == nil || *backend.ConcurrencyLimit <= 0 {
+					validation.Error(base.Key("queue_capacity"), "queue capacity requires a positive concurrency limit")
+				} else if *backend.QueueCapacity > int(^uint(0)>>1)-*backend.ConcurrencyLimit {
+					validation.Error(base.Key("queue_capacity"), "total capacity overflows int")
+				}
+			}
+			validateExtraParams(backend.ExtraParams, base.Key("extra_params"), true, validation)
+			if smokeTests := backend.SmokeTests; smokeTests != nil {
+				smokePath := base.Key("smoke_tests")
+				if smokeTests.DefaultProfile != nil {
+					if strings.TrimSpace(*smokeTests.DefaultProfile) == "" {
+						validation.Error(smokePath.Key("default_profile"), "default profile must not be blank")
+					} else if !domain.IsValidResourceID(*smokeTests.DefaultProfile) {
+						validation.Error(smokePath.Key("default_profile"), "default profile reference is malformed")
+					}
+				}
+				if authentication := smokeTests.Authentication; authentication != nil {
+					kindPath := smokePath.Key("authentication").Key("kind")
+					if authentication.Kind == nil {
+						validation.Error(kindPath, "authentication kind is required")
+					} else if *authentication.Kind != "none" && *authentication.Kind != "openrouter_key" {
+						validation.Error(kindPath, "authentication kind must be none or openrouter_key")
+					}
 				}
 			}
 		}
-	}
-	for _, id := range sortedKeys(config.Profiles) {
-		profile := config.Profiles[id]
-		base := bases.profiles.Key(id)
-		if strings.TrimSpace(id) == "" {
-			validation.Error(base, "profile ID must not be blank")
+		for _, id := range sortedKeys(resources.profiles) {
+			profile := resources.profiles[id]
+			base := resources.bases.profiles.Key(id)
+			if !domain.IsValidLocalResourceKey(id) {
+				validation.Error(base, "profile key must be a nonblank local key without a slash")
+			}
+			if profile.Backend != nil && *profile.Backend != "" {
+				if !domain.IsValidResourceID(*profile.Backend) {
+					validation.Error(base.Key("backend"), "backend reference is malformed")
+				} else if _, exists := backendIDs[*profile.Backend]; !exists {
+					validation.Error(base.Key("backend"), "backend is not defined")
+				}
+			}
+			if profile.Model != nil && *profile.Model != "" && strings.TrimSpace(*profile.Model) == "" {
+				validation.Error(base.Key("model"), "model must not be blank")
+			}
+			if profile.Temperature != nil {
+				if err := domain.ValidateExecutionTargetSettings(domain.ExecutionTarget{Temperature: *profile.Temperature}); err != nil {
+					validation.Error(base.Key("temperature"), err.Error())
+				}
+			}
+			if profile.TopP != nil {
+				if err := domain.ValidateExecutionTargetSettings(domain.ExecutionTarget{TopP: *profile.TopP}); err != nil {
+					validation.Error(base.Key("top_p"), err.Error())
+				}
+			}
+			if profile.MaxTokens != nil {
+				if err := domain.ValidateExecutionTargetSettings(domain.ExecutionTarget{MaxTokens: *profile.MaxTokens}); err != nil {
+					validation.Error(base.Key("max_tokens"), err.Error())
+				}
+			}
+			if profile.TimeoutSeconds != nil {
+				if err := domain.ValidateExecutionTargetSettings(domain.ExecutionTarget{TimeoutSeconds: *profile.TimeoutSeconds}); err != nil {
+					validation.Error(base.Key("timeout_seconds"), err.Error())
+				}
+			}
+			validateExtraParams(profile.ExtraParams, base.Key("extra_params"), false, validation)
 		}
-		if profile.Backend != nil && *profile.Backend != "" {
-			if _, exists := config.Backends[*profile.Backend]; !exists {
-				validation.Error(base.Key("backend"), "backend is not defined")
+		for _, id := range sortedKeys(resources.prompts) {
+			prompt := resources.prompts[id]
+			base := resources.bases.prompts.Key(id)
+			if !domain.IsValidLocalResourceKey(id) {
+				validation.Error(base, "prompt key must be a nonblank local key without a slash")
+			}
+			if prompt.DefaultProfile != nil && *prompt.DefaultProfile != "" && !domain.IsValidResourceID(*prompt.DefaultProfile) {
+				validation.Error(base.Key("default_profile"), "default profile reference is malformed")
 			}
 		}
-		if profile.Model != nil && *profile.Model != "" && strings.TrimSpace(*profile.Model) == "" {
-			validation.Error(base.Key("model"), "model must not be blank")
-		}
-		if profile.Temperature != nil {
-			if err := domain.ValidateExecutionTargetSettings(domain.ExecutionTarget{Temperature: *profile.Temperature}); err != nil {
-				validation.Error(base.Key("temperature"), err.Error())
-			}
-		}
-		if profile.TopP != nil {
-			if err := domain.ValidateExecutionTargetSettings(domain.ExecutionTarget{TopP: *profile.TopP}); err != nil {
-				validation.Error(base.Key("top_p"), err.Error())
-			}
-		}
-		if profile.MaxTokens != nil {
-			if err := domain.ValidateExecutionTargetSettings(domain.ExecutionTarget{MaxTokens: *profile.MaxTokens}); err != nil {
-				validation.Error(base.Key("max_tokens"), err.Error())
-			}
-		}
-		if profile.TimeoutSeconds != nil {
-			if err := domain.ValidateExecutionTargetSettings(domain.ExecutionTarget{TimeoutSeconds: *profile.TimeoutSeconds}); err != nil {
-				validation.Error(base.Key("timeout_seconds"), err.Error())
-			}
-		}
-		validateExtraParams(profile.ExtraParams, base.Key("extra_params"), false, validation)
 	}
 }
 
diff --git a/internal/configuration/load_test.go b/internal/configuration/load_test.go
index 51b5149..7efe42d 100644
--- a/internal/configuration/load_test.go
+++ b/internal/configuration/load_test.go
@@ -85,39 +85,55 @@ func TestLoadConsumesAcceptedUnderlayVersionAndValidatesHeaderlessPayload(t *tes
 
 func TestLoadComposesLiteralKeysAndEffectivePresence(t *testing.T) {
 	base := mapping("defaults", map[string]any{
+		"version": int64(1),
 		"backends": map[string]any{
 			"local.v1": map[string]any{"endpoint": "http://localhost:8080/v1", "concurrency_limit": 2},
 		},
-		"profiles": map[string]any{
-			"base/one": map[string]any{"backend": "local.v1", "temperature": 0.8, "top_p": 0.9, "api_key_required": true,
-				"extra_params": map[string]any{"provider": map[string]any{"first": 1, "second": 2}}},
-			"child.v1": map[string]any{"extends": "base/one"},
-		},
-		"prompts": map[string]any{"invoice/summary": map[string]any{
-			"version":  "v1.0",
-			"messages": []any{map[string]any{"role": "user", "content": "Summarize."}},
-			"output":   map[string]any{"format": "text", "validation_mode": "basic"},
+		"collections": map[string]any{"base": map[string]any{
+			"release_version": "",
+			"backends": map[string]any{
+				"local.v1": map[string]any{"endpoint": "http://localhost:8080/v1", "concurrency_limit": 3},
+			},
+			"profiles": map[string]any{
+				"one": map[string]any{"backend": "local.v1", "temperature": 0.8, "top_p": 0.9, "api_key_required": true,
+					"extra_params": map[string]any{"provider": map[string]any{"first": 1, "second": 2}}},
+				"child.v1":   map[string]any{"extends": "one"},
+				"namespaced": map[string]any{"backend": "base/local.v1", "model": "collection-model"},
+			},
+		}, "invoice": map[string]any{
+			"release_version": "r7",
+			"prompts": map[string]any{
+				"summary": map[string]any{
+					"version":  "v1.0",
+					"messages": []any{map[string]any{"role": "user", "content": "Summarize."}},
+					"output":   map[string]any{"format": "text", "validation_mode": "basic"},
+				},
+				"version": map[string]any{
+					"messages": []any{map[string]any{"role": "user", "content": "Nested ID."}},
+					"output":   map[string]any{"format": "text", "validation_mode": "basic"},
+				},
+			},
 		}},
 	})
 	overlay := mapping("operator", map[string]any{
 		"backends": map[string]any{"local.v1": map[string]any{"queue_capacity": 0}},
-		"profiles": map[string]any{"child.v1": map[string]any{
+		"collections": map[string]any{"base": map[string]any{"profiles": map[string]any{"child.v1": map[string]any{
 			"temperature": 0, "top_p": nil, "api_key_required": false,
 			"extra_params": map[string]any{"provider": map[string]any{"second": 3}},
-		}},
+		}}}},
 	})
-	loaded, err := load(configkit.Input{Source: configkit.NoSource()}, []configkit.Underlay{
+	loaded, err := load(mapping("main", map[string]any{"version": "1"}), []configkit.Underlay{
 		{Inputs: []configkit.Input{base}}, {Inputs: []configkit.Input{overlay}},
 	})
 	if err != nil {
 		t.Fatal(err)
 	}
-	profile := loaded.result.Config.Profiles["child.v1"]
+	profile := loaded.result.Config.Collections["base"].Profiles["child.v1"]
 	if profile.Temperature == nil || *profile.Temperature != 0 || profile.TopP != nil || profile.APIKeyRequired == nil || *profile.APIKeyRequired {
 		t.Fatalf("effective values were not retained: %+v", profile)
 	}
-	if loaded.profiles["child.v1"]["temperature"] != fieldValue || loaded.profiles["child.v1"]["top_p"] != fieldNull || loaded.profiles["child.v1"]["api_key_required"] != fieldValue {
-		t.Fatalf("effective presence was lost: %+v", loaded.profiles["child.v1"])
+	if loaded.profiles["base/child.v1"]["temperature"] != fieldValue || loaded.profiles["base/child.v1"]["top_p"] != fieldNull || loaded.profiles["base/child.v1"]["api_key_required"] != fieldValue {
+		t.Fatalf("effective presence was lost: %+v", loaded.profiles["base/child.v1"])
 	}
 	provider := profile.ExtraParams["provider"].(map[string]any)
 	if provider["first"] != int64(1) || provider["second"] != int64(3) {
@@ -127,9 +143,69 @@ func TestLoadComposesLiteralKeysAndEffectivePresence(t *testing.T) {
 	if backend.QueueCapacity == nil || *backend.QueueCapacity != 0 || loaded.backends["local.v1"]["queue_capacity"] != fieldValue {
 		t.Fatalf("explicit zero queue capacity was lost: %+v", backend)
 	}
-	if loaded.result.Config.Prompts["invoice/summary"].Messages[0].Content == nil || loaded.result.Config.Prompts["invoice/summary"].Version == nil || *loaded.result.Config.Prompts["invoice/summary"].Version != "v1.0" {
+	if _, err := loaded.registry.GetBackend("base/local.v1"); err != nil {
+		t.Fatalf("collection backend was not indexed by its full ID: %v", err)
+	}
+	collectionProfile, exists := loaded.indexedProfiles["base/namespaced"]
+	if !exists || collectionProfile.ID != "base/namespaced" || collectionProfile.ResolvedTarget == nil || collectionProfile.ResolvedTarget.BackendID != "base/local.v1" {
+		t.Fatalf("collection profile snapshot = %+v, exists %t", collectionProfile, exists)
+	}
+	if loaded.result.Config.Collections["invoice"].Prompts["summary"].Messages[0].Content == nil || loaded.result.Config.Collections["invoice"].Prompts["summary"].Version == nil || *loaded.result.Config.Collections["invoice"].Prompts["summary"].Version != "v1.0" {
 		t.Fatal("literal prompt ID and version were not decoded")
 	}
+	if loaded.result.Config.Version == nil || *loaded.result.Config.Version != "1" ||
+		loaded.result.Config.Collections["base"].ReleaseVersion == nil || *loaded.result.Config.Collections["base"].ReleaseVersion != "" ||
+		loaded.result.Config.Collections["invoice"].ReleaseVersion == nil || *loaded.result.Config.Collections["invoice"].ReleaseVersion != "r7" {
+		t.Fatalf("root or collection version metadata was not retained: %+v", loaded.result.Config)
+	}
+	if _, _, err := loaded.prompt("invoice/version"); err != nil {
+		t.Fatalf("resource named version was not indexed under its qualified identity: %v", err)
+	}
+}
+
+func TestLoadRejectsInvalidCollectionAndResourceKeys(t *testing.T) {
+	for _, test := range []struct {
+		name    string
+		values  map[string]any
+		message string
+	}{
+		{
+			name:    "namespace with separator",
+			values:  map[string]any{"collections": map[string]any{"bad/name": map[string]any{}}},
+			message: "collection namespace must be nonblank and contain no slash",
+		},
+		{
+			name: "root resource with separator",
+			values: map[string]any{"backends": map[string]any{
+				"bad/name": map[string]any{"endpoint": "https://example.test/v1"},
+			}},
+			message: "backend key must be a nonblank local key without a slash",
+		},
+		{
+			name: "collection resource with separator",
+			values: map[string]any{"collections": map[string]any{"good": map[string]any{
+				"prompts": map[string]any{"bad/name": map[string]any{
+					"messages": []any{map[string]any{"role": "user", "content": "Hello."}},
+					"output":   map[string]any{"format": "text", "validation_mode": "basic"},
+				}},
+			}}},
+			message: "prompt key must be a nonblank local key without a slash",
+		},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			_, err := load(mapping("invalid names", test.values), nil)
+			var loadErr *configkit.LoadError
+			if err == nil || !errors.As(err, &loadErr) {
+				t.Fatalf("load error = %v, want ConfigKit validation error", err)
+			}
+			for _, diagnostic := range loadErr.Diagnostics() {
+				if diagnostic.Message == test.message {
+					return
+				}
+			}
+			t.Fatalf("load diagnostics = %+v, want message %q", loadErr.Diagnostics(), test.message)
+		})
+	}
 }
 
 func TestLoadRecordsBackendNormalizationAndNullDefault(t *testing.T) {
diff --git a/internal/configuration/prompts.go b/internal/configuration/prompts.go
index 0ff01e2..5162b94 100644
--- a/internal/configuration/prompts.go
+++ b/internal/configuration/prompts.go
@@ -81,8 +81,10 @@ func resolvePrompts(prompts map[string]promptConfig, basePath configkit.Path, re
 	}
 }
 
-func (state *loaded) materializePrompts(prompts map[string]promptConfig, basePath configkit.Path) error {
-	state.prompts = make(map[string]*promptEntry, len(prompts))
+func (state *loaded) materializePrompts(prompts map[string]promptConfig, basePath configkit.Path, namespace string) error {
+	if state.prompts == nil {
+		state.prompts = make(map[string]*promptEntry)
+	}
 	var metadata *configkit.Metadata
 	lookupOrigin := func(path configkit.Path) (configkit.FieldInfo, bool) {
 		if metadata == nil {
@@ -96,11 +98,12 @@ func (state *loaded) materializePrompts(prompts map[string]promptConfig, basePat
 		if strings.TrimSpace(id) == "" {
 			return fmt.Errorf("%s: prompt ID must not be blank", promptBase)
 		}
-		entry, err := state.materializePrompt(id, prompts[id].Version, prompts[id], promptBase, lookupOrigin)
+		fullID := indexedResourceID(namespace, id)
+		entry, err := state.materializePrompt(fullID, prompts[id].Version, prompts[id], promptBase, lookupOrigin)
 		if err != nil {
 			return err
 		}
-		state.prompts[id] = entry
+		state.prompts[fullID] = entry
 	}
 	return nil
 }
diff --git a/internal/configuration/prompts_test.go b/internal/configuration/prompts_test.go
index 1820163..3e14290 100644
--- a/internal/configuration/prompts_test.go
+++ b/internal/configuration/prompts_test.go
@@ -16,8 +16,8 @@ import (
 
 func TestLoadCapturesInheritedImportedContent(t *testing.T) {
 	files := fstest.MapFS{
-		"app/main.yaml":     {Data: []byte("configkit:\n  imports:\n    - path: ../catalog/base.yaml\nprompts:\n  child:\n    extends: base\n")},
-		"catalog/base.yaml": {Data: []byte("prompts:\n  base:\n    version: \"v1\"\n    messages:\n      - role: ' USER '\n        cache_control:\n          type: ' ephemeral '\n          ttl: ' 1h '\n        content_file: ./body.md\n    output:\n      format: text\n      validation_mode: basic\n")},
+		"app/main.yaml":     {Data: []byte("configkit:\n  imports:\n    - path: ../catalog/base.yaml\ncollections:\n  docs:\n    prompts:\n      child:\n        extends: base\n")},
+		"catalog/base.yaml": {Data: []byte("collections:\n  docs:\n    release_version: r1\n    prompts:\n      base:\n        version: \"v1\"\n        messages:\n          - role: ' USER '\n            cache_control:\n              type: ' ephemeral '\n              ttl: ' 1h '\n            content_file: ./body.md\n        output:\n          format: text\n          validation_mode: basic\n")},
 		"catalog/body.md":   {Data: []byte("Captured {{.name}}")},
 	}
 	namespace := configkit.NewFilesystem("embedded", files)
@@ -32,7 +32,7 @@ func TestLoadCapturesInheritedImportedContent(t *testing.T) {
 		}
 		t.Fatal(err)
 	}
-	definition, inspection, err := state.prompt("child")
+	definition, inspection, err := state.prompt("docs/child")
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -43,7 +43,7 @@ func TestLoadCapturesInheritedImportedContent(t *testing.T) {
 	if message.Role != "user" || message.CacheControl == nil || message.CacheControl.Type != "ephemeral" || message.CacheControl.TTL != "1h" {
 		t.Fatalf("message metadata was not normalized: %+v", message)
 	}
-	field, ok := state.result.Metadata().Lookup(configkit.Keys("prompts", "child", "messages").Index(0).Key("content_file"))
+	field, ok := state.result.Metadata().Lookup(configkit.Keys("collections", "docs", "prompts", "child", "messages").Index(0).Key("content_file"))
 	if !ok || len(field.Origin.Locations) != 1 {
 		t.Fatalf("content origin was lost during normalization: %+v", field)
 	}
@@ -57,12 +57,12 @@ func TestLoadCapturesInheritedImportedContent(t *testing.T) {
 		t.Fatalf("content origin = %q, want catalog/base.yaml", originPath)
 	}
 	files["catalog/body.md"].Data = []byte("Changed")
-	again, againInspection, err := state.prompt("child")
+	again, againInspection, err := state.prompt("docs/child")
 	if err != nil || again.Templates[0].Content != "Captured {{.name}}" || againInspection.PromptHash != inspection.PromptHash {
 		t.Fatalf("captured definition changed after source mutation: %+v, %+v, %v", again, againInspection, err)
 	}
 	definition.Templates[0].Content = "caller mutation"
-	third, _, err := state.prompt("child")
+	third, _, err := state.prompt("docs/child")
 	if err != nil || third.Templates[0].Content != "Captured {{.name}}" {
 		t.Fatalf("caller mutation escaped into index: %+v, %v", third, err)
 	}
diff --git a/internal/configuration/targets.go b/internal/configuration/targets.go
index d7fd6ad..771d295 100644
--- a/internal/configuration/targets.go
+++ b/internal/configuration/targets.go
@@ -12,9 +12,11 @@ import (
 )
 
 func (state *loaded) buildExecutionProfiles() error {
-	definitions := make(map[string]domain.Backend, len(state.result.Config.Backends))
-	for _, id := range sortedKeys(state.result.Config.Backends) {
-		config := state.result.Config.Backends[id]
+	backendConfigs := indexedBackends(&state.result.Config)
+	profileConfigs := indexedProfiles(&state.result.Config)
+	definitions := make(map[string]domain.Backend, len(backendConfigs))
+	for _, id := range sortedKeys(backendConfigs) {
+		config := backendConfigs[id]
 		definition := domain.Backend{ID: id, ExtraParams: config.ExtraParams}
 		if config.SmokeTests != nil {
 			smokeTests := &domain.BackendSmokeTestConfig{DefaultProfile: config.SmokeTests.DefaultProfile}
@@ -49,9 +51,9 @@ func (state *loaded) buildExecutionProfiles() error {
 		return err
 	}
 	state.registry = registry
-	state.indexedProfiles = make(map[string]domain.ExecutionProfile, len(state.result.Config.Profiles))
-	for _, id := range sortedKeys(state.result.Config.Profiles) {
-		config := state.result.Config.Profiles[id]
+	state.indexedProfiles = make(map[string]domain.ExecutionProfile, len(profileConfigs))
+	for _, id := range sortedKeys(profileConfigs) {
+		config := profileConfigs[id]
 		fields := state.profiles[id]
 		target := defaults.ExecutionTargetDefault()
 		if config.Backend != nil && *config.Backend != "" {
diff --git a/internal/domain/resource_identity.go b/internal/domain/resource_identity.go
index d9078a9..2bb66ba 100644
--- a/internal/domain/resource_identity.go
+++ b/internal/domain/resource_identity.go
@@ -38,3 +38,27 @@ func resourceNamespaceFromID(id string) (string, bool) {
 	namespace, _, _ := strings.Cut(id, "/")
 	return namespace, true
 }
+
+// IsValidResourceID reports whether id is an unqualified resource ID or one
+// valid namespace/local-ID pair.
+func IsValidResourceID(id string) bool { return validResourceID(id) }
+
+// IsValidResourceNamespace reports whether namespace is nonblank and contains
+// no namespace separator.
+func IsValidResourceNamespace(namespace string) bool { return validResourceNamespace(namespace) }
+
+// IsValidLocalResourceKey reports whether key is a nonblank key for a
+// namespace-local resource mapping.
+func IsValidLocalResourceKey(key string) bool { return validLocalResourceKey(key) }
+
+// QualifyLocalResourceID combines a validated namespace and local mapping key.
+// An empty namespace leaves a valid unqualified key unchanged.
+func QualifyLocalResourceID(namespace, key string) (string, bool) {
+	if !validLocalResourceKey(key) || (namespace != "" && !validResourceNamespace(namespace)) {
+		return "", false
+	}
+	if namespace == "" {
+		return key, true
+	}
+	return namespace + "/" + key, true
+}
diff --git a/listing_contract_test.go b/listing_contract_test.go
index d38fe35..97e445f 100644
--- a/listing_contract_test.go
+++ b/listing_contract_test.go
@@ -111,23 +111,26 @@ func TestListIdentitiesPreserveContextErrorsWithoutPartialResults(t *testing.T)
 
 func TestListIdentitiesUseEffectiveLayeredMembership(t *testing.T) {
 	underlay := configkit.Input{Source: configkit.Mapping("consumer defaults", map[string]any{
-		"profiles": map[string]any{
-			"base/profile":    map[string]any{"endpoint": "https://example.test/v1", "model": "base-model"},
-			"child/profile":   map[string]any{"extends": "base/profile"},
-			"overlay/profile": map[string]any{"endpoint": "https://example.test/v1", "model": "old-model"},
-		},
+		"collections": map[string]any{"shared": map[string]any{
+			"profiles": map[string]any{
+				"base":    map[string]any{"endpoint": "https://example.test/v1", "model": "base-model"},
+				"child":   map[string]any{"extends": "base"},
+				"overlay": map[string]any{"endpoint": "https://example.test/v1", "model": "old-model"},
+			},
+			"prompts": map[string]any{
+				"prompt": promptDefinitionWithVersion("v1", listingContractPrompt()),
+			},
+		}},
 		"prompts": map[string]any{
-			"shared/prompt": promptDefinitionWithVersion("v1", listingContractPrompt()),
 			"underlay-only": promptDefinitionWithVersion("v1", listingContractPrompt()),
 		},
 	})}
 	main := configkit.Input{Source: configkit.Mapping("application overlay", map[string]any{
-		"profiles": map[string]any{
-			"overlay/profile": map[string]any{"model": "effective-model"},
-		},
+		"collections": map[string]any{"shared": map[string]any{"profiles": map[string]any{
+			"overlay": map[string]any{"model": "effective-model"},
+		}}},
 		"prompts": map[string]any{
-			"shared/prompt": promptDefinitionWithVersion("v2", listingContractPrompt()),
-			"main-only":     promptDefinitionWithVersion("v3", listingContractPrompt()),
+			"main-only": promptDefinitionWithVersion("v3", listingContractPrompt()),
 		},
 	})}
 	engine, err := promptkit.NewEngine(promptkit.Config{Sources: promptkit.ConfigurationSources{
@@ -143,24 +146,24 @@ func TestListIdentitiesUseEffectiveLayeredMembership(t *testing.T) {
 		t.Fatal(err)
 	}
 	for _, id := range []string{
-		"base/profile", "child/profile", "overlay/profile",
+		"shared/base", "shared/child", "shared/overlay",
 		"promptkit-openrouter-standard", "promptkit-openrouter-auto",
 	} {
 		if !containsListingProfile(profiles, id) {
 			t.Errorf("profile listing %#v does not include %q", profiles, id)
 		}
 	}
-	for _, id := range []string{"base/profile", "child/profile", "overlay/profile"} {
+	for _, id := range []string{"shared/base", "shared/child", "shared/overlay"} {
 		if got := countListingProfile(profiles, id); got != 1 {
 			t.Errorf("profile %q appears %d times, want 1", id, got)
 		}
 	}
 
-	overlay, err := engine.InspectProfile(context.Background(), "overlay/profile")
+	overlay, err := engine.InspectProfile(context.Background(), "shared/overlay")
 	if err != nil || overlay == nil || overlay.EffectiveModelParams.Model != "effective-model" {
 		t.Fatalf("overlay profile did not resolve to its effective definition: (%+v, %v)", overlay, err)
 	}
-	child, err := engine.InspectProfile(context.Background(), "child/profile")
+	child, err := engine.InspectProfile(context.Background(), "shared/child")
 	if err != nil || child == nil || child.EffectiveModelParams.Model != "base-model" {
 		t.Fatalf("inherited child profile did not resolve its effective definition: (%+v, %v)", child, err)
 	}
@@ -171,13 +174,13 @@ func TestListIdentitiesUseEffectiveLayeredMembership(t *testing.T) {
 	}
 	wantPrompts := []promptkit.PromptIdentity{
 		{ID: "main-only", Version: stringPointerForTest("v3")},
-		{ID: "shared/prompt", Version: stringPointerForTest("v2")},
+		{ID: "shared/prompt", Version: stringPointerForTest("v1")},
 		{ID: "underlay-only", Version: stringPointerForTest("v1")},
 	}
 	if !reflect.DeepEqual(prompts, wantPrompts) {
 		t.Fatalf("effective prompt identities = %#v, want %#v", prompts, wantPrompts)
 	}
-	if got := countListingPrompt(prompts, "shared/prompt", "v2"); got != 1 {
+	if got := countListingPrompt(prompts, "shared/prompt", "v1"); got != 1 {
 		t.Fatalf("overlaid prompt identity appears %d times, want 1", got)
 	}
 }