diff --git a/docs/consumers/pkg-promptkit.md b/docs/consumers/pkg-promptkit.md
index 7b5e93d..61b13a7 100644
--- a/docs/consumers/pkg-promptkit.md
+++ b/docs/consumers/pkg-promptkit.md
@@ -884,6 +884,12 @@ secret-handling policies.
 
 ## Extension Interfaces
 
+JSON Schema validation and native structured output use a self-contained root
+document. Internal references are supported; references to other files or
+network resources fail during preparation. `WithSchemaFile` selects one root
+file, while `WithSchemaFS` and `SchemaDir` select a root source. Prepared
+executions retain their captured schema even if the source later changes.
+
 Inject an [`LLMClient` or `ArtifactReader`](../../types.go) when the built-in
 behavior does not fit the application. Their GoDoc defines concurrent use,
 context handling, ownership of copied values, nil responses, and preservation
diff --git a/docs/formats.md b/docs/formats.md
index ad7f38e..c173467 100644
--- a/docs/formats.md
+++ b/docs/formats.md
@@ -418,8 +418,9 @@ generic inheritance and layer mechanics, consult
 ## Schemas
 
 Schemas are JSON documents selected by a prompt or request `schema_path`.
-Directory and `fs.FS` schema paths resolve within the configured root;
-referenced nested schemas resolve relative to the owning schema document.
+Directory and `fs.FS` schema paths resolve within the configured root. Each
+schema must be self-contained: in-document references, IDs, and anchors are
+supported, but references requiring another file or network resource fail.
 `WithSchemaFile` exposes one schema under its base name. An unreadable,
 invalid, or unresolvable schema causes an operational validation error.
 Valid JSON that fails the schema instead yields a failed validation result.
diff --git a/docs/internal/sources.md b/docs/internal/sources.md
index ead6dbf..0e8f060 100644
--- a/docs/internal/sources.md
+++ b/docs/internal/sources.md
@@ -216,10 +216,10 @@ instead of first making a response-sized string copy.
 
 Every preparation operation creates one operation-local validation plan. None,
 basic, and JSON modes retain the effective output contract without source
-access. JSON Schema mode loads the root document once, resolves and compiles
-each transitive reference, and retains the compiled validator. Schema compiler
-resources use canonical escaped file or private-scheme URLs; loaders decode
-their paths once and enforce the configured source boundary. The
+access. JSON Schema mode loads the root document once, compiles its declared
+schema locations, and retains the compiled root validator. External resources
+are rejected without file or network loading; in-document references remain
+supported. Root resources use canonical escaped file or private-scheme URLs. The
 provider-facing structured-output metadata uses the root document captured by
 the same plan.
 
diff --git a/docs/roadmap/implementation.md b/docs/roadmap/implementation.md
index 16c638f..cb915b0 100644
--- a/docs/roadmap/implementation.md
+++ b/docs/roadmap/implementation.md
@@ -375,6 +375,10 @@ recursive/dynamic references, embedded dialects, and independent instances.
 validate/engine tests finish the schema transition. No local-only mode, bundler,
 new dialect, or release/publication prerequisite is introduced.
 
+Completion: schema-file option, frozen preparation, native submission, and
+external-reference rejection are covered through public APIs. Root, validation,
+and engine tests pass on Go 1.27.3; current schema guidance is aligned.
+
 ## Stage 14: Merge Provider Maps Into One Owned Lower Copy
 
 **Catalog:** 19. **Files:** configuration targets and focused overlay tests.
diff --git a/engine.go b/engine.go
index a8e5649..4f57a74 100644
--- a/engine.go
+++ b/engine.go
@@ -213,7 +213,8 @@ func WithSchemaFS(fsys fs.FS, root string) Option {
 //
 // Prompt schema_path values refer to the file's base name. path must name an
 // existing non-directory file when NewEngine applies the option. This option
-// replaces Config.SchemaDir and earlier schema-source options.
+// replaces Config.SchemaDir and earlier schema-source options. The selected
+// schema must be self-contained; external resources are not loaded.
 func WithSchemaFile(path string) Option {
 	return optionFunc(func(options *engineOptions) error {
 		return options.internal.SetSchemaFile(path)
diff --git a/internal/engine/engine.go b/internal/engine/engine.go
index 3369564..a6e2a70 100644
--- a/internal/engine/engine.go
+++ b/internal/engine/engine.go
@@ -73,7 +73,7 @@ func (o *Options) SetSchemaFS(fsys fs.FS, root string) error {
 
 // SetSchemaFile selects a single schema file.
 func (o *Options) SetSchemaFile(path string) error {
-	fsys, root, _, err := fileSource(path)
+	fsys, root, err := fileSource(path)
 	if err != nil {
 		return err
 	}
@@ -208,23 +208,23 @@ func validateSourceFS(fsys fs.FS, root string) error {
 	return nil
 }
 
-func fileSource(name string) (fs.FS, string, string, error) {
+func fileSource(name string) (fs.FS, string, error) {
 	if strings.TrimSpace(name) == "" {
-		return nil, "", "", fmt.Errorf("source path is required")
+		return nil, "", fmt.Errorf("source path is required")
 	}
 	directory := filepath.Dir(name)
 	base := filepath.Base(name)
 	if base == "." || base == string(filepath.Separator) {
-		return nil, "", "", fmt.Errorf("source path must name a file")
+		return nil, "", fmt.Errorf("source path must name a file")
 	}
 	info, err := os.Stat(name)
 	if err != nil {
-		return nil, "", "", fmt.Errorf("failed to access source file %q: %w", name, err)
+		return nil, "", fmt.Errorf("failed to access source file %q: %w", name, err)
 	}
 	if info.IsDir() {
-		return nil, "", "", fmt.Errorf("source path %q must be a file", name)
+		return nil, "", fmt.Errorf("source path %q must be a file", name)
 	}
-	return os.DirFS(directory), filepath.ToSlash(base), directory, nil
+	return os.DirFS(directory), filepath.ToSlash(base), nil
 }
 
 func (e *Engine) InspectPrompt(ctx context.Context, id string) (*domain.PromptInspection, error) {
diff --git a/prepared_execution_contract_test.go b/prepared_execution_contract_test.go
index fc53369..70ff4cd 100644
--- a/prepared_execution_contract_test.go
+++ b/prepared_execution_contract_test.go
@@ -813,8 +813,9 @@ func preparedSchemaSource() fstest.MapFS {
   "title": "original root",
   "type": "object",
   "required": ["value"],
+  "$defs": {"value": {"type":"integer", "minimum":2}},
   "properties": {
-    "value": {"$ref": "value.json"}
+    "value": {"$ref": "#/$defs/value"}
   }
 }`)},
 		"value.json": &fstest.MapFile{Data: []byte(`{
diff --git a/schema_file_contract_test.go b/schema_file_contract_test.go
new file mode 100644
index 0000000..c221918
--- /dev/null
+++ b/schema_file_contract_test.go
@@ -0,0 +1,90 @@
+package promptkit_test
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"io"
+	"net/http"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"go.maximumdirect.net/configkit"
+	"go.maximumdirect.net/promptkit"
+)
+
+func TestSchemaFilePreparationAndNativeSubmission(t *testing.T) {
+	firstDir, secondDir := t.TempDir(), t.TempDir()
+	first, second := filepath.Join(firstDir, "schema.json"), filepath.Join(secondDir, "schema.json")
+	if err := os.WriteFile(first, []byte(`{"type":"string"}`), 0600); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(second, []byte(`{"$defs":{"value":{"type":"integer"}},"$ref":"#/$defs/value"}`), 0600); err != nil {
+		t.Fatal(err)
+	}
+	input := configkit.Input{Source: configkit.Mapping("schema test", map[string]any{
+		"profiles": []any{map[string]any{"id": "profile", "endpoint": "https://example.invalid/v1", "model": "model"}},
+		"prompts":  []any{map[string]any{"id": "prompt", "default_profile": "profile", "messages": []any{map[string]any{"role": "user", "content": "hello"}}, "output": map[string]any{"format": "json", "validation_mode": "json_schema", "schema_path": "schema.json"}}},
+	})}
+	var payload map[string]any
+	client := &http.Client{Transport: roundTripFunc(func(request *http.Request) (*http.Response, error) {
+		if err := json.NewDecoder(request.Body).Decode(&payload); err != nil {
+			t.Fatal(err)
+		}
+		return &http.Response{StatusCode: 200, Header: make(http.Header), Body: io.NopCloser(strings.NewReader(`{"choices":[{"message":{"content":"3"}}]}`))}, nil
+	})}
+	engine, err := promptkit.NewEngine(promptkit.Config{HTTPClient: client, Sources: promptkit.ConfigurationSources{Main: &input}}, promptkit.WithSchemaFile(first), promptkit.WithSchemaFile(second))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := engine.ValidateRequest(context.Background(), promptkit.RunRequest{PromptID: "prompt"}); err != nil {
+		t.Fatalf("validate request: %v", err)
+	}
+	prepared, err := engine.PrepareExecution(context.Background(), promptkit.RunRequest{PromptID: "prompt"})
+	if err != nil || prepared.Details().StructuredOutput == nil {
+		t.Fatalf("prepared = %+v, %v", prepared, err)
+	}
+	if err := os.Remove(second); err != nil {
+		t.Fatal(err)
+	}
+	result, err := engine.RunPrepared(context.Background(), prepared)
+	if err != nil || result.Validation.Status != promptkit.ValidationPassed {
+		t.Fatalf("run = %+v, %v", result, err)
+	}
+	encoded, err := json.Marshal(payload["response_format"])
+	if err != nil || !strings.Contains(string(encoded), `"$defs"`) || !strings.Contains(string(encoded), `#/$defs/value`) {
+		t.Fatalf("wire schema = %s, %v", encoded, err)
+	}
+	if _, err := engine.PrepareExecution(context.Background(), promptkit.RunRequest{PromptID: "prompt"}); !errors.Is(err, promptkit.ErrValidation) {
+		t.Fatalf("missing root error = %v", err)
+	}
+}
+
+func TestSchemaFileRejectsInvalidSourcesAndExternalReferences(t *testing.T) {
+	dir := t.TempDir()
+	for _, name := range []string{filepath.Join(dir, "missing.json"), dir} {
+		if _, err := promptkit.NewEngine(promptkit.Config{}, promptkit.WithSchemaFile(name)); !errors.Is(err, promptkit.ErrInvalidConfig) {
+			t.Fatalf("source %q = %v", name, err)
+		}
+	}
+	root := filepath.Join(dir, "schema.json")
+	if err := os.WriteFile(root, []byte(`{"$defs":{"unused":{"$ref":"other.json"}}}`), 0600); err != nil {
+		t.Fatal(err)
+	}
+	input := configkit.Input{Source: configkit.Mapping("schema test", map[string]any{
+		"profiles": []any{map[string]any{"id": "profile", "endpoint": "https://example.invalid/v1", "model": "model"}},
+		"prompts":  []any{map[string]any{"id": "prompt", "default_profile": "profile", "messages": []any{map[string]any{"role": "user", "content": "hello"}}, "output": map[string]any{"format": "json", "validation_mode": "json_schema", "schema_path": "schema.json"}}},
+	})}
+	calls := 0
+	client := &http.Client{Transport: roundTripFunc(func(*http.Request) (*http.Response, error) { calls++; return nil, errors.New("unexpected dispatch") })}
+	engine, err := promptkit.NewEngine(promptkit.Config{HTTPClient: client, Sources: promptkit.ConfigurationSources{Main: &input}}, promptkit.WithSchemaFile(root))
+	if err != nil {
+		t.Fatal(err)
+	}
+	_, err = engine.Run(context.Background(), promptkit.RunRequest{PromptID: "prompt"})
+	if !errors.Is(err, promptkit.ErrValidation) || calls != 0 {
+		t.Fatalf("external reference = %v, calls = %d", err, calls)
+	}
+}