diff --git a/docs/config.md b/docs/config.md
index 8f09570..ea4999b 100644
--- a/docs/config.md
+++ b/docs/config.md
@@ -846,12 +846,21 @@ source acquisition. Unused and root registrations are allowed and have no effect
 Registration controls strict composition and supplies identity fields for parent
 lookup when surviving records in that sequence use `extends`. Dynamic selectors
 apply at strict-composition and inheritance destinations without requiring the
-application to enumerate mapping keys. Each underlay group
-and the main tier has independent duplicate-identity state. Precedence assembly
-is unchanged: a present higher-priority sequence replaces the lower sequence as
-one value, including at a registered path. Registration does not add a final
-identity check to defaults, application resolution, or the published typed
-configuration. The accepted rationale is recorded in
+application to enumerate mapping keys. Each underlay group and the main tier has
+independent duplicate-identity state. Precedence assembly is unchanged: a present
+higher-priority sequence replaces the lower sequence as one value, including at a
+registered path.
+
+After effective secret lookup, the shared load lifecycle validates every matching
+sequence in the final typed projection before application semantic validation.
+This catches identities introduced by typed defaults, CLI assignment, or recorded
+resolution, in both ordinary and layered loads. Only actual sequences are checked;
+absent paths and other shapes remain the schema or application validator's concern.
+Identity fields are read from effective typed payload regardless of authored
+presence. Diagnostics use concrete collection and item paths and available source
+locations, and never include identity or credential values. The guarantee ends at
+successful publication; later caller mutations are outside it. The accepted
+rationale is recorded in
 [ADR 0014](adr/0014-sequence-placement-and-composition.md).
 The [maintained prompt catalog](consumers/README.md#identified-prompt-sequences)
 shows item path and glob imports, helper-supplied identity, and main-tier
diff --git a/docs/roadmap/implementation.md b/docs/roadmap/implementation.md
index 951f175..9b00077 100644
--- a/docs/roadmap/implementation.md
+++ b/docs/roadmap/implementation.md
@@ -1,6 +1,6 @@
 # Sequence Identity And Combination Implementation Plan
 
-Status: implementation in progress; Stages 1–26 complete.
+Status: implementation in progress; Stages 1–27 complete.
 
 Audience: a Luna coding agent implementing one numbered stage per prompt, in
 order. This plan starts at commit
@@ -913,6 +913,15 @@ Scope: the final-result guarantee, not another combination or inheritance phase.
 Validation: final identity, selector, facade, defaults/resolution/override, and
 secret tests plus the everyday check.
 
+**Completion:** Added shared final identity validation to the ordinary and layered
+load lifecycle after effective secret lookup and before application validation.
+It traverses the final typed projection with compiled selectors and reports
+concrete paths and available locations without exposing identity or credential
+values. Added facade and lifecycle coverage for late defaults, CLI, resolution,
+dynamic namespaces, typed numeric equality, ignored unmatched shapes, and nil
+results on failure. Updated registration comments and the configuration contract.
+Verified focused facade and engine tests plus `./scripts/check.sh`.
+
 ## Stage 28 — Exercise Representative Consumer Workflows
 
 Scope: a small number of meaningful integrations, not a Cartesian test matrix.
diff --git a/facade_final_sequence_identity_test.go b/facade_final_sequence_identity_test.go
new file mode 100644
index 0000000..124e462
--- /dev/null
+++ b/facade_final_sequence_identity_test.go
@@ -0,0 +1,201 @@
+package configkit_test
+
+import (
+	"strings"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/ConfigKit"
+)
+
+func TestFinalSequenceIdentityValidatesLateValues(t *testing.T) {
+	identity := configkit.SequenceIdentityAt(configkit.Keys("items"), "id")
+	for _, source := range []string{"defaults", "CLI", "resolution"} {
+		for _, shape := range []string{"duplicate", "missing", "non-scalar"} {
+			t.Run(source+"/"+shape, func(t *testing.T) {
+				items := finalIdentityRecords(shape)
+				definition := configkit.Definition[map[string]any]{
+					SequenceIdentities: []configkit.SequenceIdentity{identity},
+					Defaults: func() map[string]any {
+						if source == "defaults" {
+							return map[string]any{"items": items}
+						}
+						return map[string]any{}
+					},
+				}
+				options := configkit.Options[map[string]any]{Definition: definition}
+				switch source {
+				case "CLI":
+					options.Overrides = []configkit.Override{{Path: configkit.Keys("items"), Value: items, Flag: "--items"}}
+				case "resolution":
+					options.Definition.Resolve = func(value *map[string]any, resolution *configkit.Resolution) error {
+						(*value)["items"] = items
+						resolution.Record(configkit.Keys("items"), configkit.ChangeNormalization, "create effective records")
+						return nil
+					}
+				}
+				result, err := configkit.Load(configkit.NoSource(), options)
+				if result != nil {
+					t.Fatalf("invalid final identities returned a result: %#v", result.Config)
+				}
+				loadErr := requireFacadeLoadError(t, err)
+				if len(loadErr.Diagnostics()) != 1 {
+					t.Fatalf("diagnostics = %#v", loadErr.Diagnostics())
+				}
+				diagnostic := loadErr.Diagnostics()[0]
+				wantCode, wantPath := configkit.CodeSequenceInvalid, "/items/0/id"
+				if shape == "duplicate" {
+					wantCode, wantPath = configkit.CodeSequenceConflict, "/items"
+				}
+				if diagnostic.Code != wantCode || diagnostic.Path.String() != wantPath {
+					t.Fatalf("diagnostic = %#v, want %s at %s", diagnostic, wantCode, wantPath)
+				}
+				if source == "CLI" && (diagnostic.Primary == nil || diagnostic.Primary.SourceID != "source-1") {
+					t.Fatalf("CLI identity diagnostic lost its source: %#v", diagnostic)
+				}
+			})
+		}
+	}
+}
+
+func TestFinalSequenceIdentityMatchesLateDynamicNamespaces(t *testing.T) {
+	selector := configkit.SequenceSelector{
+		configkit.SequenceLiteralKey("collections"),
+		configkit.SequenceAnyMappingKey(),
+		configkit.SequenceLiteralKey("items"),
+	}
+	for _, source := range []string{"defaults", "CLI", "resolution"} {
+		t.Run(source, func(t *testing.T) {
+			name := map[string]string{"defaults": "team", "CLI": "cloud", "resolution": "orbit"}[source]
+			path := configkit.Keys("collections", name, "items")
+			items := finalIdentityRecords("duplicate")
+			definition := configkit.Definition[map[string]any]{
+				SequenceIdentities: []configkit.SequenceIdentity{
+					configkit.SequenceIdentityMatching(selector, "id"),
+				},
+				Defaults: func() map[string]any {
+					if source == "defaults" {
+						return map[string]any{"collections": map[string]any{name: map[string]any{"items": items}}}
+					}
+					return map[string]any{}
+				},
+			}
+			options := configkit.Options[map[string]any]{Definition: definition}
+			switch source {
+			case "CLI":
+				options.Overrides = []configkit.Override{{Path: path, Value: items, Flag: "--items"}}
+			case "resolution":
+				options.Definition.Resolve = func(value *map[string]any, resolution *configkit.Resolution) error {
+					(*value)["collections"] = map[string]any{name: map[string]any{"items": items}}
+					resolution.Record(configkit.Keys("collections"), configkit.ChangeNormalization, "create namespaced records")
+					return nil
+				}
+			}
+			result, err := configkit.Load(configkit.NoSource(), options)
+			if result != nil {
+				t.Fatalf("invalid dynamic identity returned a result: %#v", result.Config)
+			}
+			loadErr := requireFacadeLoadError(t, err)
+			if diagnostics := loadErr.Diagnostics(); len(diagnostics) != 1 || diagnostics[0].Code != configkit.CodeSequenceConflict || diagnostics[0].Path.String() != path.String() {
+				t.Fatalf("dynamic identity diagnostics = %#v", diagnostics)
+			}
+		})
+	}
+}
+
+func TestFinalSequenceIdentityAppliesToLayeredLoads(t *testing.T) {
+	definition := configkit.Definition[map[string]any]{
+		SequenceIdentities: []configkit.SequenceIdentity{configkit.SequenceIdentityAt(configkit.Keys("items"), "id")},
+		Defaults: func() map[string]any {
+			return map[string]any{"items": finalIdentityRecords("duplicate")}
+		},
+	}
+	result, err := configkit.LoadLayered(configkit.Input{Source: configkit.NoSource()}, configkit.LayeredOptions[map[string]any]{Definition: definition})
+	if result != nil {
+		t.Fatalf("invalid layered final identities returned a result: %#v", result.Config)
+	}
+	loadErr := requireFacadeLoadError(t, err)
+	if diagnostics := loadErr.Diagnostics(); len(diagnostics) != 1 || diagnostics[0].Code != configkit.CodeSequenceConflict {
+		t.Fatalf("layered identity diagnostics = %#v", diagnostics)
+	}
+}
+
+func TestFinalSequenceIdentityUsesTypedNumbersAndIgnoresUnmatchedShapes(t *testing.T) {
+	definition := configkit.Definition[map[string]any]{
+		SequenceIdentities: []configkit.SequenceIdentity{
+			configkit.SequenceIdentityAt(configkit.Keys("items"), "id"),
+			configkit.SequenceIdentityAt(configkit.Keys("unmatched"), "id"),
+		},
+	}
+	_, err := configkit.Load(configkit.NoSource(), configkit.Options[map[string]any]{
+		Definition: configkit.Definition[map[string]any]{
+			SequenceIdentities: definition.SequenceIdentities,
+			Defaults: func() map[string]any {
+				return map[string]any{"items": []any{
+					map[string]any{"id": int64(1)}, map[string]any{"id": float64(1)},
+				}}
+			},
+		},
+	})
+	loadErr := requireFacadeLoadError(t, err)
+	if diagnostics := loadErr.Diagnostics(); len(diagnostics) != 1 || diagnostics[0].Code != configkit.CodeSequenceConflict {
+		t.Fatalf("typed numeric identity diagnostics = %#v", diagnostics)
+	}
+
+	valid, err := configkit.Load(configkit.Mapping("valid", map[string]any{
+		"items": []any{
+			map[string]any{"id": nil}, map[string]any{"id": true},
+			map[string]any{"id": int64(1)}, map[string]any{"id": "one"},
+		},
+		"other": []any{map[string]any{"id": "same"}, map[string]any{"id": "same"}},
+	}), configkit.Options[map[string]any]{Definition: definition})
+	if err != nil || valid == nil {
+		t.Fatalf("valid scalar identities and unmatched duplicate sequence = %#v, %v", valid, err)
+	}
+	if _, err := configkit.Load(configkit.Mapping("other-shapes", map[string]any{"items": nil}), configkit.Options[map[string]any]{Definition: definition}); err != nil {
+		t.Fatalf("null at a registered path was validated as an identity sequence: %v", err)
+	}
+}
+
+func TestFinalSequenceIdentityDiagnosticDoesNotRevealResolvedSecrets(t *testing.T) {
+	const canary = "FINAL-IDENTITY-CREDENTIAL-CANARY"
+	const secretName = "CONFIGKIT_FINAL_IDENTITY_SECRET"
+	t.Setenv(secretName, canary)
+	type item struct {
+		ID    string           `yaml:"id"`
+		Token configkit.Secret `yaml:"token"`
+	}
+	type config struct {
+		Items []item `yaml:"items"`
+	}
+	definition := configkit.Definition[config]{
+		SequenceIdentities: []configkit.SequenceIdentity{configkit.SequenceIdentityAt(configkit.Keys("items"), "id")},
+		Defaults: func() config {
+			return config{Items: []item{
+				{ID: "duplicate", Token: configkit.SecretEnv(secretName)},
+				{ID: "duplicate", Token: configkit.SecretEnv(secretName)},
+			}}
+		},
+	}
+	result, err := configkit.Load(configkit.NoSource(), configkit.Options[config]{Definition: definition})
+	if result != nil {
+		t.Fatalf("duplicate identity returned a result: %#v", result.Config)
+	}
+	if err == nil || strings.Contains(err.Error(), canary) {
+		t.Fatalf("identity diagnostic leaked a resolved secret: %v", err)
+	}
+	loadErr := requireFacadeLoadError(t, err)
+	if diagnostics := loadErr.Diagnostics(); len(diagnostics) != 1 || diagnostics[0].Code != configkit.CodeSequenceConflict {
+		t.Fatalf("secret-bearing identity diagnostics = %#v", diagnostics)
+	}
+}
+
+func finalIdentityRecords(shape string) []any {
+	switch shape {
+	case "duplicate":
+		return []any{map[string]any{"id": "same"}, map[string]any{"id": "same"}}
+	case "missing":
+		return []any{map[string]any{"other": "value"}}
+	default:
+		return []any{map[string]any{"id": map[string]any{"nested": "value"}}}
+	}
+}
diff --git a/internal/engine/final_identity.go b/internal/engine/final_identity.go
new file mode 100644
index 0000000..64012cb
--- /dev/null
+++ b/internal/engine/final_identity.go
@@ -0,0 +1,51 @@
+package engine
+
+import "gitea.maximumdirect.net/eric/ConfigKit/internal/document"
+
+func validateFinalSequenceIdentities(root *document.Node, policy sequencePolicy) []Diagnostic {
+	if root == nil || policy.selectorTrie == nil {
+		return nil
+	}
+	var diagnostics []Diagnostic
+	var visit func(*document.Node, Path, []*sequenceSelectorTrie)
+	visit = func(node *document.Node, path Path, states []*sequenceSelectorTrie) {
+		if node == nil {
+			return
+		}
+		if node.Kind == document.Sequence {
+			var fields []string
+			for _, state := range states {
+				if state.terminal {
+					fields = state.fields
+					break
+				}
+			}
+			if fields != nil {
+				_, issues := validateNormalizedSequenceIdentityFrom(node, path, fields, sequenceIdentityDiagnosticCodes{
+					invalid: CodeSequenceInvalid, conflict: CodeSequenceConflict,
+				}, 0)
+				diagnostics = append(diagnostics, issues...)
+			}
+			return
+		}
+		if node.Kind != document.Mapping {
+			return
+		}
+		for _, entry := range node.Mapping {
+			next := make([]*sequenceSelectorTrie, 0, len(states)*2)
+			for _, state := range states {
+				if literal := state.literals[entry.Key]; literal != nil {
+					next = append(next, literal)
+				}
+				if state.wildcard != nil {
+					next = append(next, state.wildcard)
+				}
+			}
+			if len(next) != 0 {
+				visit(entry.Value, path.Key(entry.Key), next)
+			}
+		}
+	}
+	visit(root, Path{}, []*sequenceSelectorTrie{policy.selectorTrie})
+	return canonicalDiagnostics(diagnostics)
+}
diff --git a/internal/engine/load.go b/internal/engine/load.go
index d1a531f..d868293 100644
--- a/internal/engine/load.go
+++ b/internal/engine/load.go
@@ -331,6 +331,11 @@ func executeLoadRequest[T any](request loadRequest[T], secrets SecretBinding, lo
 	if hasErrors(secretResolution.diagnostics) {
 		return nil, accumulator.loadError()
 	}
+	identityDiagnostics := validateFinalSequenceIdentities(resolved.referenceInput, request.sequencePolicy)
+	accumulator.add(identityDiagnostics...)
+	if hasErrors(identityDiagnostics) {
+		return nil, accumulator.loadError()
+	}
 	if request.definition.Validate != nil {
 		diagnostics = runValidation(&configuration, request.definition.Validate, schema, resolved.final, resolved.referenceInput, secretResolution.lookups)
 		accumulator.add(diagnostics...)
diff --git a/internal/engine/sequence_registration_test.go b/internal/engine/sequence_registration_test.go
index 04b345a..ebfbec2 100644
--- a/internal/engine/sequence_registration_test.go
+++ b/internal/engine/sequence_registration_test.go
@@ -388,7 +388,7 @@ func TestRegisteredSequencePolicyAcrossLoadingLifecycle(t *testing.T) {
 		}
 	})
 
-	t.Run("replacement overlay validates identities and CLI may introduce duplicates", func(t *testing.T) {
+	t.Run("replacement overlay and CLI validate final identities", func(t *testing.T) {
 		directory := t.TempDir()
 		mainPath := writeImportFile(t, directory, "main.yml", "items: [{id: base}]\n")
 		writeImportFile(t, directory, "overlays/testing.yml", "items: [{id: duplicate}, {id: duplicate}]\n")
@@ -401,8 +401,8 @@ func TestRegisteredSequencePolicyAcrossLoadingLifecycle(t *testing.T) {
 			Definition: definition,
 			Overrides:  []Override{{Path: Keys("items"), Flag: "--items", Value: []any{map[string]any{"id": "duplicate"}, map[string]any{"id": "duplicate"}}}},
 		})
-		if err != nil || len(result.Config.Items) != 2 {
-			t.Fatalf("replacement CLI value = %#v, %v", result, err)
+		if result != nil || loadCode(t, err) != CodeSequenceConflict {
+			t.Fatalf("duplicate CLI value = %#v, %v", result, err)
 		}
 
 		resolved := definition
@@ -412,31 +412,23 @@ func TestRegisteredSequencePolicyAcrossLoadingLifecycle(t *testing.T) {
 			return nil
 		}
 		result, err = testLoad[config](Bytes("main", []byte("items: [{id: first}, {id: second}]\n")), Options[config]{Definition: resolved})
-		if err != nil {
-			t.Fatalf("resolver replacement error code = %s", loadCode(t, err))
-		}
-		if len(result.Config.Items) != 2 {
-			t.Fatalf("resolver replacement = %#v, %v", result, err)
+		if result != nil || loadCode(t, err) != CodeSequenceConflict {
+			t.Fatalf("resolver duplicate = %#v, %v", result, err)
 		}
 	})
 
-	t.Run("application validation can reject replacement duplicates", func(t *testing.T) {
+	t.Run("final identity validation precedes application validation", func(t *testing.T) {
 		checked := definition
+		validated := false
 		checked.Validate = func(value *config, validation *Validation) {
-			seen := make(map[string]bool)
-			for index, entry := range value.Items {
-				if seen[entry.ID] {
-					validation.Error(Keys("items").Index(index).Key("id"), "identity must be unique")
-				}
-				seen[entry.ID] = true
-			}
+			validated = true
 		}
 		_, err := testLoad[config](Bytes("main", []byte("items: [{id: base}]\n")), Options[config]{
 			Definition: checked,
 			Overrides:  []Override{{Path: Keys("items"), Flag: "--items", Value: []any{map[string]any{"id": "duplicate"}, map[string]any{"id": "duplicate"}}}},
 		})
-		if got := loadCode(t, err); got != CodeValidateError {
-			t.Fatalf("application validation error = %s", got)
+		if got := loadCode(t, err); got != CodeSequenceConflict || validated {
+			t.Fatalf("duplicate identity result = %s, validation callback invoked %v", got, validated)
 		}
 	})
 }
diff --git a/sequence_identity.go b/sequence_identity.go
index 49ab258..cc72d3d 100644
--- a/sequence_identity.go
+++ b/sequence_identity.go
@@ -25,8 +25,8 @@ func SequenceAnyMappingKey() SequenceSelectorSegment {
 }
 
 // SequenceIdentity records the identity fields used for strict sequence
-// composition and identified-record parent lookup. It does not add final-result
-// identity validation; that check remains the application's responsibility.
+// composition, identified-record parent lookup, and final typed-result
+// validation during loading.
 type SequenceIdentity struct {
 	exactPath      bool
 	path           Path
@@ -34,9 +34,9 @@ type SequenceIdentity struct {
 	identityFields []string
 }
 
-// SequenceIdentityAt registers identity fields at an exact mapping path. The
-// path and fields are copied; invalid paths and empty field sets are reported
-// during load validation.
+// SequenceIdentityAt registers an exact mapping path for strict-composition,
+// inheritance, and final typed-result identity checks. The path and fields are
+// copied; invalid paths and empty field sets are reported during load validation.
 func SequenceIdentityAt(path Path, fields ...string) SequenceIdentity {
 	return SequenceIdentity{
 		exactPath:      true,
@@ -46,8 +46,9 @@ func SequenceIdentityAt(path Path, fields ...string) SequenceIdentity {
 }
 
 // SequenceIdentityMatching registers identity fields at destinations matched by
-// selector. Literal and wildcard selector segments are copied. Empty field sets
-// are reported during load validation.
+// selector for strict composition, inheritance, and final typed-result checks.
+// Literal and wildcard selector segments are copied. Empty field sets are
+// reported during load validation.
 func SequenceIdentityMatching(selector SequenceSelector, fields ...string) SequenceIdentity {
 	return SequenceIdentity{
 		selector:       append(SequenceSelector(nil), selector...),