diff --git a/packages/react/src/context/providers/AssistantProvider.tsx b/packages/react/src/context/providers/AssistantProvider.tsx
index a66fcd4a7..58a4e1332 100644
--- a/packages/react/src/context/providers/AssistantProvider.tsx
+++ b/packages/react/src/context/providers/AssistantProvider.tsx
@@ -1,3 +1,5 @@
+"use client";
+
 import type { FC, PropsWithChildren } from "react";
 import { useEffect, useInsertionEffect, useRef, useState } from "react";
 import type { AssistantRuntime } from "../../runtime";
diff --git a/packages/react/src/context/react/AssistantContext.ts b/packages/react/src/context/react/AssistantContext.ts
index 498883d13..956ea86b6 100644
--- a/packages/react/src/context/react/AssistantContext.ts
+++ b/packages/react/src/context/react/AssistantContext.ts
@@ -1,3 +1,5 @@
+"use client";
+
 import { createContext, useContext } from "react";
 import type { AssistantModelConfigState } from "../stores/AssistantModelConfig";
 import type { AssistantToolUIsState } from "../stores/AssistantToolUIs";
diff --git a/packages/react/src/context/react/ContentPartContext.ts b/packages/react/src/context/react/ContentPartContext.ts
index 23d17f34d..8e98d2c02 100644
--- a/packages/react/src/context/react/ContentPartContext.ts
+++ b/packages/react/src/context/react/ContentPartContext.ts
@@ -1,3 +1,5 @@
+"use client";
+
 import { createContext, useContext } from "react";
 import type { ContentPartState } from "../stores/ContentPart";
 import { ReadonlyStore } from "../ReadonlyStore";
diff --git a/packages/react/src/context/react/MessageContext.ts b/packages/react/src/context/react/MessageContext.ts
index fadd73a99..17bb8a534 100644
--- a/packages/react/src/context/react/MessageContext.ts
+++ b/packages/react/src/context/react/MessageContext.ts
@@ -1,3 +1,5 @@
+"use client";
+
 import { createContext, useContext } from "react";
 import type { MessageState } from "../stores/Message";
 import type { EditComposerState } from "../stores/EditComposer";
diff --git a/packages/react/src/context/react/ThreadContext.ts b/packages/react/src/context/react/ThreadContext.ts
index 51f7257b7..6c9b11fd2 100644
--- a/packages/react/src/context/react/ThreadContext.ts
+++ b/packages/react/src/context/react/ThreadContext.ts
@@ -1,3 +1,5 @@
+"use client";
+
 import { createContext, useContext } from "react";
 import type { ComposerState } from "../stores/Composer";
 import type { ThreadState } from "../stores/Thread";
diff --git a/packages/react/src/runtime/local/ChatModelAdapter.tsx b/packages/react/src/runtime/local/ChatModelAdapter.tsx
index 24cf8dd81..f08c49e4d 100644
--- a/packages/react/src/runtime/local/ChatModelAdapter.tsx
+++ b/packages/react/src/runtime/local/ChatModelAdapter.tsx
@@ -17,5 +17,5 @@ export type ChatModelRunOptions = {
 };
 
 export type ChatModelAdapter = {
-  run: (options: ChatModelRunOptions) => Promise<ChatModelRunResult>;
+  run: (options: ChatModelRunOptions) => Promise<ChatModelRunResult | void>;
 };
diff --git a/packages/react/src/runtime/local/LocalRuntime.tsx b/packages/react/src/runtime/local/LocalRuntime.tsx
index fc3e72a15..09bd6177b 100644
--- a/packages/react/src/runtime/local/LocalRuntime.tsx
+++ b/packages/react/src/runtime/local/LocalRuntime.tsx
@@ -10,7 +10,7 @@ import {
 import type { Unsubscribe } from "../../types/Unsubscribe";
 import { ThreadRuntime } from "../core";
 import { MessageRepository } from "../utils/MessageRepository";
-import { generateId } from "../utils/idUtils";
+import { generateId } from "../../utils/idUtils";
 import { BaseAssistantRuntime } from "../core/BaseAssistantRuntime";
 import type { ChatModelAdapter, ChatModelRunResult } from "./ChatModelAdapter";
 
@@ -128,12 +128,15 @@ class LocalThreadRuntime implements ThreadRuntime {
         config: mergeModelConfigs(this._configProviders),
         onUpdate: updateHandler,
       });
-      updateHandler(result);
+      if (result !== undefined) {
+        updateHandler(result);
+      }
 
       message.status = "done";
       this.repository.addOrUpdateMessage(parentId, { ...message });
     } catch (e) {
-      message.status = "error";
+      (message as any).status = "error";
+      (message as any).error = e;
       this.repository.addOrUpdateMessage(parentId, { ...message });
       console.error(e);
     } finally {
diff --git a/packages/react/src/runtime/utils/MessageRepository.tsx b/packages/react/src/runtime/utils/MessageRepository.tsx
index debbb7e83..845ef8e1f 100644
--- a/packages/react/src/runtime/utils/MessageRepository.tsx
+++ b/packages/react/src/runtime/utils/MessageRepository.tsx
@@ -1,5 +1,5 @@
 import type { ThreadMessage } from "../../types/AssistantTypes";
-import { generateOptimisticId } from "./idUtils";
+import { generateOptimisticId } from "../../utils/idUtils";
 
 type RepositoryParent = {
   children: string[];
diff --git a/packages/react/src/types/AssistantTypes.ts b/packages/react/src/types/AssistantTypes.ts
index 832ddb87b..084e242bb 100644
--- a/packages/react/src/types/AssistantTypes.ts
+++ b/packages/react/src/types/AssistantTypes.ts
@@ -35,21 +35,36 @@ export type AssistantContentPart =
 
 export type AppendContentPart = TextContentPart | ImageContentPart;
 
-export type BaseMessage = {
+type MessageCommonProps = {
   id: string;
   createdAt: Date;
 };
 
-export type UserMessage = BaseMessage & {
+type MessageStatusProps =
+  | {
+      status: "in_progress" | "done";
+      error?: undefined;
+    }
+  | {
+      status: "error";
+      error: unknown;
+    };
+
+export type SystemMessage = MessageCommonProps & {
+  role: "system";
+  content: [TextContentPart];
+};
+
+export type UserMessage = MessageCommonProps & {
   role: "user";
   content: UserContentPart[];
 };
 
-export type AssistantMessage = BaseMessage & {
-  role: "assistant";
-  content: AssistantContentPart[];
-  status: "in_progress" | "done" | "error";
-};
+export type AssistantMessage = MessageCommonProps &
+  MessageStatusProps & {
+    role: "assistant";
+    content: AssistantContentPart[];
+  };
 
 export type AppendMessage = {
   parentId: string | null;
@@ -57,4 +72,25 @@ export type AppendMessage = {
   content: AppendContentPart[];
 };
 
-export type ThreadMessage = UserMessage | AssistantMessage;
+export type ThreadMessage = SystemMessage | UserMessage | AssistantMessage;
+
+/** Core Message Types (without UI content parts) */
+
+export type CoreUserContentPart = TextContentPart | ImageContentPart;
+export type CoreAssistantContentPart = TextContentPart | ToolCallContentPart;
+
+export type CoreUserMessage = MessageCommonProps & {
+  role: "user";
+  content: CoreUserContentPart[];
+};
+
+export type CoreAssistantMessage = MessageCommonProps &
+  MessageStatusProps & {
+    role: "assistant";
+    content: CoreAssistantContentPart[];
+  };
+
+export type CoreThreadMessage =
+  | SystemMessage
+  | CoreUserMessage
+  | CoreAssistantMessage;
diff --git a/packages/react/src/types/index.ts b/packages/react/src/types/index.ts
index 906f78b00..e00bd6b44 100644
--- a/packages/react/src/types/index.ts
+++ b/packages/react/src/types/index.ts
@@ -10,6 +10,13 @@ export type {
   ImageContentPart,
   ToolCallContentPart,
   UIContentPart,
+
+  // core message types
+  CoreUserContentPart,
+  CoreAssistantContentPart,
+  CoreUserMessage,
+  CoreAssistantMessage,
+  CoreThreadMessage,
 } from "./AssistantTypes";
 
 export type {
diff --git a/packages/react/src/utils/combined/createCombinedStore.ts b/packages/react/src/utils/combined/createCombinedStore.ts
index 82e98cd5a..c22f24f43 100644
--- a/packages/react/src/utils/combined/createCombinedStore.ts
+++ b/packages/react/src/utils/combined/createCombinedStore.ts
@@ -1,3 +1,5 @@
+"use client";
+
 import { useSyncExternalStore } from "react";
 import type { Unsubscribe } from "../../types/Unsubscribe";
 import { ReadonlyStore } from "../../context/ReadonlyStore";
diff --git a/packages/react/src/runtime/utils/idUtils.tsx b/packages/react/src/utils/idUtils.tsx
similarity index 100%
rename from packages/react/src/runtime/utils/idUtils.tsx
rename to packages/react/src/utils/idUtils.tsx