diff --git a/packages/lang-core/package.json b/packages/lang-core/package.json
index c7063a6d0..4773a1223 100644
--- a/packages/lang-core/package.json
+++ b/packages/lang-core/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@openuidev/lang-core",
-  "version": "0.2.8",
+  "version": "0.2.9",
   "description": "Framework-agnostic core for OpenUI Lang: parser, prompt generation, validation, and type definitions",
   "license": "MIT",
   "type": "module",
diff --git a/packages/lang-core/src/__tests__/library.test.ts b/packages/lang-core/src/__tests__/library.test.ts
index 7c877ccc1..fbdbf617b 100644
--- a/packages/lang-core/src/__tests__/library.test.ts
+++ b/packages/lang-core/src/__tests__/library.test.ts
@@ -166,6 +166,27 @@ describe("per-library registry", () => {
     expect(spec.schema).toEqual(lib.toJSONSchema());
   });
 
+  it("toSpec carries the createLibrary id, omitted when unset", () => {
+    const Text = defineComponent({
+      name: "TextContent",
+      props: z.object({ text: z.string() }),
+      description: "text",
+      component: Dummy,
+    });
+
+    const named = createLibrary({
+      components: [Text],
+      root: "TextContent",
+      id: "acme-support@3",
+    });
+    expect(named.id).toBe("acme-support@3");
+    expect(named.toSpec().id).toBe("acme-support@3");
+
+    const anonymous = createLibrary({ components: [Text], root: "TextContent" });
+    expect(anonymous.id).toBeUndefined();
+    expect("id" in anonymous.toSpec()).toBe(false);
+  });
+
   it("toJSONSchema carries defineComponent descriptions on $defs entries", () => {
     const Text = defineComponent({
       name: "TextContent",
diff --git a/packages/lang-core/src/library.ts b/packages/lang-core/src/library.ts
index 4008ab5bf..98af3bfe3 100644
--- a/packages/lang-core/src/library.ts
+++ b/packages/lang-core/src/library.ts
@@ -336,6 +336,7 @@ export interface Library<C = unknown> {
   readonly components: Record<string, DefinedComponent<any, C>>;
   readonly componentGroups: ComponentGroup[] | undefined;
   readonly root: string | undefined;
+  readonly id: string | undefined;
 
   prompt(options?: PromptOptions): string;
   toSpec(): PromptSpec;
@@ -346,6 +347,7 @@ export interface LibraryDefinition<C = unknown> {
   components: DefinedComponent<any, C>[];
   componentGroups?: ComponentGroup[];
   root?: string;
+  id?: string;
 }
 
 /**
@@ -371,6 +373,7 @@ export function createLibrary<C = unknown>(input: LibraryDefinition<C>): Library
     components: componentsRecord,
     componentGroups: input.componentGroups,
     root: input.root,
+    id: input.id,
 
     prompt(options?: PromptOptions): string {
       const spec: PromptSpec = {
@@ -388,6 +391,7 @@ export function createLibrary<C = unknown>(input: LibraryDefinition<C>): Library
         components: buildComponentSpecs(componentsRecord, reg),
         componentGroups: input.componentGroups,
         schema: buildJSONSchema(),
+        ...(input.id !== undefined ? { id: input.id } : {}),
       };
     },
 
diff --git a/packages/lang-core/src/parser/prompt.ts b/packages/lang-core/src/parser/prompt.ts
index d5dce4907..302ca80ce 100644
--- a/packages/lang-core/src/parser/prompt.ts
+++ b/packages/lang-core/src/parser/prompt.ts
@@ -27,6 +27,7 @@ export interface ComponentGroup {
 }
 
 export interface BaseSpec {
+  id?: string;
   root?: string;
   components: Record<string, ComponentPromptSpec>;
   componentGroups?: ComponentGroup[];