diff --git a/src/app/chat/__tests__/chat-area.helpers.test.ts b/src/app/chat/__tests__/chat-area.helpers.test.ts
index 04d44b81..6a014e0d 100644
--- a/src/app/chat/__tests__/chat-area.helpers.test.ts
+++ b/src/app/chat/__tests__/chat-area.helpers.test.ts
@@ -10,12 +10,13 @@ import {
 describe("chat area render items", () => {
   it("keeps local message keys stable when history is prepended", () => {
     const localMessage: UiMessage = {
+      displayId: "client:message:local-1",
       content: "optimistic message",
       isFromAI: false,
       date: "2026-07-08",
     };
     const historyMessage: UiMessage = {
-      id: "history-msg-1",
+      displayId: "history-msg-1",
       content: "history message",
       isFromAI: true,
       date: "2026-07-07",
@@ -28,12 +29,34 @@ describe("chat area render items", () => {
       getMessageKey,
     );
 
-    expect(findMessageKey(firstItems, localMessage)).toBe("local-msg-1");
-    expect(findMessageKey(secondItems, localMessage)).toBe("local-msg-1");
+    expect(findMessageKey(firstItems, localMessage)).toBe(
+      "msg-client:message:local-1",
+    );
+    expect(findMessageKey(secondItems, localMessage)).toBe(
+      "msg-client:message:local-1",
+    );
     expect(findMessageKey(secondItems, historyMessage)).toBe(
       "msg-history-msg-1",
     );
   });
+
+  it("derives the same key after a message object is recreated", () => {
+    const getMessageKey = createChatMessageKeyResolver();
+    const original: UiMessage = {
+      displayId: "server:message-1:assistant",
+      remoteId: "message-1",
+      content: "Original",
+      isFromAI: true,
+      date: "2026-07-20",
+    };
+    const updated: UiMessage = {
+      ...original,
+      content: "Unlocked",
+      locked: false,
+    };
+
+    expect(getMessageKey(updated)).toBe(getMessageKey(original));
+  });
 });
 
 function findMessageKey(
diff --git a/src/app/chat/__tests__/chat-unlock-coordinator.test.ts b/src/app/chat/__tests__/chat-unlock-coordinator.test.ts
index 4b5ab8a8..8c7de576 100644
--- a/src/app/chat/__tests__/chat-unlock-coordinator.test.ts
+++ b/src/app/chat/__tests__/chat-unlock-coordinator.test.ts
@@ -9,6 +9,7 @@ import { createChatPromotionState } from "@/stores/chat/helper/promotion";
 import {
   resolveChatUnlockReturnUrl,
   resolveMessageUnlockRequest,
+  resolvePendingUnlockDisplayMessageId,
   shouldResumePendingChatUnlock,
 } from "../hooks/use-chat-unlock-coordinator";
 
@@ -31,11 +32,15 @@ describe("chat unlock coordinator", () => {
   it("creates a regular message unlock request with its remote id", () => {
     expect(
       resolveMessageUnlockRequest(
-        { messageId: "message-1", kind: "private" },
+        {
+          displayMessageId: "server:message-1:assistant",
+          remoteMessageId: "message-1",
+          kind: "private",
+        },
         defaultScope,
       ),
     ).toEqual({
-      displayMessageId: "message-1",
+      displayMessageId: "server:message-1:assistant",
       messageId: "message-1",
       kind: "private",
       returnUrl: "/chat",
@@ -51,7 +56,11 @@ describe("chat unlock coordinator", () => {
 
     expect(
       resolveMessageUnlockRequest(
-        { messageId: "image-1", kind: "image" },
+        {
+          displayMessageId: "image-1",
+          remoteMessageId: "image-1",
+          kind: "image",
+        },
         imageScope,
       ).returnUrl,
     ).toBe("/chat?image=image-1");
@@ -62,7 +71,10 @@ describe("chat unlock coordinator", () => {
 
     expect(
       resolveMessageUnlockRequest(
-        { messageId: "promotion:promotion-1", kind: "image" },
+        {
+          displayMessageId: "promotion:promotion-1",
+          kind: "image",
+        },
         { ...defaultScope, promotion },
       ),
     ).toEqual({
@@ -83,7 +95,11 @@ describe("chat unlock coordinator", () => {
 
     expect(
       resolveMessageUnlockRequest(
-        { messageId: "promotion-message-1", kind: "image" },
+        {
+          displayMessageId: "promotion:promotion-1",
+          remoteMessageId: "promotion-message-1",
+          kind: "image",
+        },
         { ...defaultScope, promotion },
       ).messageId,
     ).toBe("promotion-message-1");
@@ -103,6 +119,40 @@ describe("chat unlock coordinator", () => {
     ).toBe(true);
   });
 
+  it("maps a legacy pending remote id to the current display identity", () => {
+    const pending = createPendingUnlock({
+      displayMessageId: "message-1",
+      messageId: "message-1",
+      kind: "private",
+      returnUrl: "/chat",
+    });
+
+    expect(
+      resolvePendingUnlockDisplayMessageId(
+        pending,
+        [
+          {
+            displayId: "server:message-1:user",
+            remoteId: "message-1",
+            content: "Question",
+            isFromAI: false,
+            date: "2026-07-20",
+          },
+          {
+            displayId: "server:message-1:assistant",
+            remoteId: "message-1",
+            content: "Locked reply",
+            isFromAI: true,
+            date: "2026-07-20",
+            locked: true,
+            lockReason: "private_message",
+          },
+        ],
+        null,
+      ),
+    ).toBe("server:message-1:assistant");
+  });
+
   it("only resumes an image return when its message matches the overlay", () => {
     const imageScope = {
       defaultReturnUrl: "/chat",
@@ -136,7 +186,7 @@ describe("chat unlock coordinator", () => {
 
     expect(
       resolveMessageUnlockRequest(
-        { messageId: imageMessageId, kind: "image" },
+        { displayMessageId: imageMessageId, kind: "image" },
         {
           ...imageScope,
           promotion,
diff --git a/src/app/chat/chat-render-items.ts b/src/app/chat/chat-render-items.ts
index 4dd4f9d9..daa565b0 100644
--- a/src/app/chat/chat-render-items.ts
+++ b/src/app/chat/chat-render-items.ts
@@ -7,20 +7,7 @@ export type ChatRenderItem =
   | { type: "msg"; message: UiMessage; key: string };
 
 export function createChatMessageKeyResolver(): ChatMessageKeyResolver {
-  const localMessageKeys = new WeakMap<UiMessage, string>();
-  let nextLocalMessageKey = 0;
-
-  return (message) => {
-    if (message.id && message.id.length > 0) return `msg-${message.id}`;
-
-    const existing = localMessageKeys.get(message);
-    if (existing) return existing;
-
-    nextLocalMessageKey += 1;
-    const next = `local-msg-${nextLocalMessageKey}`;
-    localMessageKeys.set(message, next);
-    return next;
-  };
+  return (message) => `msg-${message.displayId}`;
 }
 
 export function buildChatRenderItems(
diff --git a/src/app/chat/chat-screen.tsx b/src/app/chat/chat-screen.tsx
index 196d59e3..3b3030bf 100644
--- a/src/app/chat/chat-screen.tsx
+++ b/src/app/chat/chat-screen.tsx
@@ -89,7 +89,10 @@ export function ChatScreen() {
     () =>
       imageMessageId
         ? visibleMessages.find(
-            (item) => item.id === imageMessageId && item.imageUrl,
+            (item) =>
+              (item.displayId === imageMessageId ||
+                item.remoteId === imageMessageId) &&
+              item.imageUrl,
           ) ?? null
         : null,
     [imageMessageId, visibleMessages],
@@ -175,24 +178,46 @@ export function ChatScreen() {
     state.characterErrorCode,
   ]);
 
-  function handleUnlockPrivateMessage(messageId: string): void {
-    unlockCoordinator.requestMessageUnlock(messageId, "private");
-  }
-
-  function handleUnlockVoiceMessage(messageId: string): void {
-    unlockCoordinator.requestMessageUnlock(messageId, "voice");
-  }
-
-  function handleUnlockImageMessage(messageId: string): void {
-    unlockCoordinator.requestMessageUnlock(messageId, "image");
-  }
-
-  function handleOpenImage(messageId: string): void {
-    router.push(buildChatImageOverlayUrl(messageId, characterRoutes.chat), {
-      scroll: false,
+  function handleUnlockPrivateMessage(
+    displayMessageId: string,
+    remoteMessageId?: string,
+  ): void {
+    unlockCoordinator.requestMessageUnlock({
+      displayMessageId,
+      remoteMessageId,
+      kind: "private",
     });
   }
 
+  function handleUnlockVoiceMessage(
+    displayMessageId: string,
+    remoteMessageId?: string,
+  ): void {
+    unlockCoordinator.requestMessageUnlock({
+      displayMessageId,
+      remoteMessageId,
+      kind: "voice",
+    });
+  }
+
+  function handleUnlockImageMessage(
+    displayMessageId: string,
+    remoteMessageId?: string,
+  ): void {
+    unlockCoordinator.requestMessageUnlock({
+      displayMessageId,
+      remoteMessageId,
+      kind: "image",
+    });
+  }
+
+  function handleOpenImage(displayMessageId: string): void {
+    router.push(
+      buildChatImageOverlayUrl(displayMessageId, characterRoutes.chat),
+      { scroll: false },
+    );
+  }
+
   function handleCloseImageViewer(): void {
     router.replace(
       buildChatWithoutImageOverlayUrl(searchParams, characterRoutes.chat),
@@ -201,8 +226,12 @@ export function ChatScreen() {
   }
 
   function handleUnlockImagePaywall(): void {
-    if (!imageMessageId) return;
-    unlockCoordinator.requestMessageUnlock(imageMessageId, "image");
+    if (!selectedImageMessage) return;
+    unlockCoordinator.requestMessageUnlock({
+      displayMessageId: selectedImageMessage.displayId,
+      remoteMessageId: selectedImageMessage.remoteId,
+      kind: "image",
+    });
   }
 
   return (
@@ -279,12 +308,12 @@ export function ChatScreen() {
         {selectedImageMessage?.imageUrl ? (
           <FullscreenImageViewer
             characterId={state.characterId}
-            messageId={selectedImageMessage.id}
+            remoteMessageId={selectedImageMessage.remoteId}
             imageUrl={selectedImageMessage.imageUrl}
             imagePaywalled={selectedImageMessage.imagePaywalled === true}
             isUnlockingImagePaywall={
               state.isUnlockingMessage &&
-              state.unlockingMessageId === selectedImageMessage.id
+              state.unlockingMessageId === selectedImageMessage.displayId
             }
             onUnlockImagePaywall={handleUnlockImagePaywall}
             onClose={handleCloseImageViewer}
diff --git a/src/app/chat/components/__tests__/chat-area-scroll.test.tsx b/src/app/chat/components/__tests__/chat-area-scroll.test.tsx
index ec26c8f3..1f847de4 100644
--- a/src/app/chat/components/__tests__/chat-area-scroll.test.tsx
+++ b/src/app/chat/components/__tests__/chat-area-scroll.test.tsx
@@ -265,19 +265,19 @@ function createTouchEvent(
   return event;
 }
 
-function createMessage(id: string): UiMessage {
+function createMessage(displayId: string): UiMessage {
   return {
-    id,
-    content: `Message ${id}`,
+    displayId,
+    content: `Message ${displayId}`,
     isFromAI: true,
     date: "2026-07-15",
   };
 }
 
-function createUserMessage(id: string): UiMessage {
+function createUserMessage(displayId: string): UiMessage {
   return {
-    id,
-    content: `Message ${id}`,
+    displayId,
+    content: `Message ${displayId}`,
     isFromAI: false,
     date: "2026-07-15",
   };
diff --git a/src/app/chat/components/__tests__/tailwind-components.test.tsx b/src/app/chat/components/__tests__/tailwind-components.test.tsx
index bd396795..2626bd17 100644
--- a/src/app/chat/components/__tests__/tailwind-components.test.tsx
+++ b/src/app/chat/components/__tests__/tailwind-components.test.tsx
@@ -128,7 +128,8 @@ describe("chat Tailwind components", () => {
     const openableHtml = renderToStaticMarkup(
       <ImageBubble
         characterId="elio"
-        messageId="message-1"
+        displayMessageId="server:message-1:assistant"
+        remoteMessageId="message-1"
         imageUrl="/chat-image.png"
         onOpenImage={() => undefined}
       />,
@@ -136,6 +137,7 @@ describe("chat Tailwind components", () => {
     const paywalledHtml = renderToStaticMarkup(
       <ImageBubble
         characterId="elio"
+        displayMessageId="server:message-2:assistant"
         imageUrl="/locked-image.png"
         imagePaywalled
       />,
diff --git a/src/app/chat/components/chat-area.tsx b/src/app/chat/components/chat-area.tsx
index e52053dd..83eda484 100644
--- a/src/app/chat/components/chat-area.tsx
+++ b/src/app/chat/components/chat-area.tsx
@@ -54,13 +54,18 @@ export interface ChatAreaProps {
   isLoadingMoreHistory?: boolean;
   isUnlockingMessage?: boolean;
   unlockingMessageId?: string | null;
-  onUnlockPrivateMessage?: (messageId: string) => void;
-  onUnlockVoiceMessage?: (messageId: string) => void;
-  onUnlockImageMessage?: (messageId: string) => void;
-  onOpenImage?: (messageId: string) => void;
+  onUnlockPrivateMessage?: ChatMessageAction;
+  onUnlockVoiceMessage?: ChatMessageAction;
+  onUnlockImageMessage?: ChatMessageAction;
+  onOpenImage?: (displayMessageId: string) => void;
   onLoadMoreHistory?: () => void;
 }
 
+type ChatMessageAction = (
+  displayMessageId: string,
+  remoteMessageId?: string,
+) => void;
+
 export function ChatArea({
   characterId,
   messages,
@@ -278,10 +283,10 @@ function renderMessagesWithDateHeaders(
   getMessageKey: ChatMessageKeyResolver,
   isUnlockingMessage?: boolean,
   unlockingMessageId?: string | null,
-  onUnlockPrivateMessage?: (messageId: string) => void,
-  onUnlockVoiceMessage?: (messageId: string) => void,
-  onUnlockImageMessage?: (messageId: string) => void,
-  onOpenImage?: (messageId: string) => void,
+  onUnlockPrivateMessage?: ChatMessageAction,
+  onUnlockVoiceMessage?: ChatMessageAction,
+  onUnlockImageMessage?: ChatMessageAction,
+  onOpenImage?: (displayMessageId: string) => void,
 ) {
   return buildChatRenderItems(messages, getMessageKey).map((item) =>
     item.type === "date" ? (
@@ -290,7 +295,8 @@ function renderMessagesWithDateHeaders(
       <MessageBubble
         characterId={characterId}
         key={item.key}
-        messageId={item.message.id}
+        displayMessageId={item.message.displayId}
+        remoteMessageId={item.message.remoteId}
         content={item.message.content}
         imageUrl={item.message.imageUrl}
         imagePaywalled={item.message.imagePaywalled}
@@ -302,7 +308,7 @@ function renderMessagesWithDateHeaders(
         privateMessageHint={item.message.privateMessageHint}
         isUnlockingMessage={
           isUnlockingMessage === true &&
-          item.message.id === unlockingMessageId
+          item.message.displayId === unlockingMessageId
         }
         onUnlockPrivateMessage={onUnlockPrivateMessage}
         onUnlockVoiceMessage={onUnlockVoiceMessage}
diff --git a/src/app/chat/components/chat-media-image.tsx b/src/app/chat/components/chat-media-image.tsx
index d4a8850a..05be45c0 100644
--- a/src/app/chat/components/chat-media-image.tsx
+++ b/src/app/chat/components/chat-media-image.tsx
@@ -13,7 +13,7 @@ import { useCachedChatMediaUrl } from "@/lib/chat/use_cached_chat_media_url";
 
 export interface ChatMediaImageProps {
   characterId: string;
-  messageId?: string;
+  remoteMessageId?: string;
   remoteUrl: string;
   alt?: string;
   className?: string;
@@ -30,7 +30,7 @@ export interface ChatMediaImageProps {
 
 export function ChatMediaImage({
   characterId,
-  messageId,
+  remoteMessageId,
   remoteUrl,
   alt = "",
   className,
@@ -48,7 +48,7 @@ export function ChatMediaImage({
   const { mediaUrl, isUsingCachedMedia, reportMediaError } =
     useCachedChatMediaUrl({
       characterId,
-      messageId,
+      messageId: remoteMessageId,
       remoteUrl,
       kind: "image",
     });
diff --git a/src/app/chat/components/fullscreen-image-viewer.tsx b/src/app/chat/components/fullscreen-image-viewer.tsx
index 317bf49b..bc1f236f 100644
--- a/src/app/chat/components/fullscreen-image-viewer.tsx
+++ b/src/app/chat/components/fullscreen-image-viewer.tsx
@@ -19,7 +19,7 @@ import styles from "./fullscreen-image-viewer.module.css";
 
 export interface FullscreenImageViewerProps {
   characterId: string;
-  messageId?: string;
+  remoteMessageId?: string;
   imageUrl: string;
   imagePaywalled?: boolean;
   isUnlockingImagePaywall?: boolean;
@@ -29,7 +29,7 @@ export interface FullscreenImageViewerProps {
 
 export function FullscreenImageViewer({
   characterId,
-  messageId,
+  remoteMessageId,
   imageUrl,
   imagePaywalled = false,
   isUnlockingImagePaywall = false,
@@ -54,7 +54,7 @@ export function FullscreenImageViewer({
       >
         <ChatMediaImage
           characterId={characterId}
-          messageId={messageId}
+          remoteMessageId={remoteMessageId}
           remoteUrl={imageUrl}
           className={styles.paywallImage}
           nativeClassName={`${styles.nativePaywallImage} ${styles.paywallImage}`}
@@ -104,7 +104,7 @@ export function FullscreenImageViewer({
       />
       <ChatMediaImage
         characterId={characterId}
-        messageId={messageId}
+        remoteMessageId={remoteMessageId}
         remoteUrl={imageUrl}
         className={styles.viewerImage}
         errorClassName="error"
diff --git a/src/app/chat/components/image-bubble.tsx b/src/app/chat/components/image-bubble.tsx
index 59a6bafa..4c7f4bbc 100644
--- a/src/app/chat/components/image-bubble.tsx
+++ b/src/app/chat/components/image-bubble.tsx
@@ -12,20 +12,22 @@ import { ChatMediaImage } from "./chat-media-image";
 
 export interface ImageBubbleProps {
   characterId: string;
-  messageId?: string;
+  displayMessageId: string;
+  remoteMessageId?: string;
   imageUrl: string; // base64 data URI 或 URL
   imagePaywalled?: boolean;
-  onOpenImage?: (messageId: string) => void;
+  onOpenImage?: (displayMessageId: string) => void;
 }
 
 export function ImageBubble({
   characterId,
-  messageId,
+  displayMessageId,
+  remoteMessageId,
   imageUrl,
   imagePaywalled = false,
   onOpenImage,
 }: ImageBubbleProps) {
-  const canOpen = Boolean(messageId && onOpenImage);
+  const canOpen = Boolean(onOpenImage);
   const imageClassName = [
     "block h-auto w-full object-cover",
     imagePaywalled ? "scale-104 blur-sm" : "",
@@ -34,8 +36,8 @@ export function ImageBubble({
     .join(" ");
 
   const openImage = () => {
-    if (!messageId || !onOpenImage) return;
-    onOpenImage(messageId);
+    if (!onOpenImage) return;
+    onOpenImage(displayMessageId);
   };
 
   return (
@@ -55,7 +57,7 @@ export function ImageBubble({
     >
       <ChatMediaImage
         characterId={characterId}
-        messageId={messageId}
+        remoteMessageId={remoteMessageId}
         remoteUrl={imageUrl}
         className={imageClassName}
         errorClassName="flex size-(--chat-media-size,220px) items-center justify-center bg-(--color-bubble-background,#fff) text-(length:--icon-size-xl,24px) text-(--color-text-secondary,#9e9e9e)"
diff --git a/src/app/chat/components/message-bubble.tsx b/src/app/chat/components/message-bubble.tsx
index 726a4fb2..32ae6665 100644
--- a/src/app/chat/components/message-bubble.tsx
+++ b/src/app/chat/components/message-bubble.tsx
@@ -16,7 +16,8 @@ import styles from "./chat-area.module.css";
 
 export interface MessageBubbleProps {
   characterId: string;
-  messageId?: string;
+  displayMessageId: string;
+  remoteMessageId?: string;
   content: string;
   imageUrl?: string | null;
   imagePaywalled?: boolean;
@@ -27,15 +28,21 @@ export interface MessageBubbleProps {
   lockedPrivate?: boolean | null;
   privateMessageHint?: string | null;
   isUnlockingMessage?: boolean;
-  onUnlockPrivateMessage?: (messageId: string) => void;
-  onUnlockVoiceMessage?: (messageId: string) => void;
-  onUnlockImageMessage?: (messageId: string) => void;
-  onOpenImage?: (messageId: string) => void;
+  onUnlockPrivateMessage?: ChatMessageAction;
+  onUnlockVoiceMessage?: ChatMessageAction;
+  onUnlockImageMessage?: ChatMessageAction;
+  onOpenImage?: (displayMessageId: string) => void;
 }
 
+type ChatMessageAction = (
+  displayMessageId: string,
+  remoteMessageId?: string,
+) => void;
+
 export function MessageBubble({
   characterId,
-  messageId,
+  displayMessageId,
+  remoteMessageId,
   content,
   imageUrl,
   imagePaywalled,
@@ -57,18 +64,19 @@ export function MessageBubble({
     return (
       <div
         className={styles.bubbleRowAi}
-        data-chat-message-id={messageId}
+        data-chat-message-id={displayMessageId}
         aria-label="AI message"
       >
         <MessageAvatar isFromAI={true} />
         <div className={styles.bubbleInlineSpacer} aria-hidden="true" />
         <MessageContent
           characterId={characterId}
+          displayMessageId={displayMessageId}
+          remoteMessageId={remoteMessageId}
           content={content}
           imageUrl={imageUrl}
           imagePaywalled={imagePaywalled}
           audioUrl={audioUrl}
-          messageId={messageId}
           isFromAI={true}
           locked={locked}
           lockReason={lockReason}
@@ -88,17 +96,18 @@ export function MessageBubble({
   return (
     <div
       className={styles.bubbleRowUser}
-      data-chat-message-id={messageId}
+      data-chat-message-id={displayMessageId}
       aria-label="User message"
     >
       <div className={styles.bubbleAvatarSpacer} aria-hidden="true" />
       <MessageContent
         characterId={characterId}
+        displayMessageId={displayMessageId}
+        remoteMessageId={remoteMessageId}
         content={content}
         imageUrl={imageUrl}
         imagePaywalled={imagePaywalled}
         audioUrl={audioUrl}
-        messageId={messageId}
         isFromAI={false}
         locked={locked}
         lockReason={lockReason}
diff --git a/src/app/chat/components/message-content.tsx b/src/app/chat/components/message-content.tsx
index 5332849f..82e0ee5f 100644
--- a/src/app/chat/components/message-content.tsx
+++ b/src/app/chat/components/message-content.tsx
@@ -8,32 +8,39 @@ import styles from "./chat-area.module.css";
 
 export interface MessageContentProps {
   characterId: string;
+  displayMessageId: string;
+  remoteMessageId?: string;
   content: string;
   imageUrl?: string | null;
   imagePaywalled?: boolean;
   audioUrl?: string | null;
-  messageId?: string;
   isFromAI: boolean;
   locked?: boolean | null;
   lockReason?: string | null;
   lockedPrivate?: boolean | null;
   privateMessageHint?: string | null;
   isUnlockingMessage?: boolean;
-  onUnlockPrivateMessage?: (messageId: string) => void;
-  onUnlockVoiceMessage?: (messageId: string) => void;
-  onUnlockImageMessage?: (messageId: string) => void;
-  onOpenImage?: (messageId: string) => void;
+  onUnlockPrivateMessage?: ChatMessageAction;
+  onUnlockVoiceMessage?: ChatMessageAction;
+  onUnlockImageMessage?: ChatMessageAction;
+  onOpenImage?: (displayMessageId: string) => void;
 }
 
+type ChatMessageAction = (
+  displayMessageId: string,
+  remoteMessageId?: string,
+) => void;
+
 const IMAGE_PLACEHOLDER = "[图片]";
 
 export function MessageContent({
   characterId,
+  displayMessageId,
+  remoteMessageId,
   content,
   imageUrl,
   imagePaywalled,
   audioUrl,
-  messageId,
   isFromAI,
   locked,
   lockReason,
@@ -57,16 +64,17 @@ export function MessageContent({
     (lockReason === "image_paywall" || lockReason === "image");
   const shouldRenderVoiceMessage = hasAudio || isLockedVoiceMessage;
   const handleUnlockPrivateMessage =
-    messageId && onUnlockPrivateMessage
-      ? () => onUnlockPrivateMessage(messageId)
+    onUnlockPrivateMessage
+      ? () =>
+          onUnlockPrivateMessage(displayMessageId, remoteMessageId)
       : undefined;
   const handleUnlockVoiceMessage =
-    isLockedVoiceMessage && messageId && onUnlockVoiceMessage
-      ? () => onUnlockVoiceMessage(messageId)
+    isLockedVoiceMessage && onUnlockVoiceMessage
+      ? () => onUnlockVoiceMessage(displayMessageId, remoteMessageId)
       : undefined;
   const handleUnlockImageMessage =
-    isLockedImageMessage && messageId && onUnlockImageMessage
-      ? () => onUnlockImageMessage(messageId)
+    isLockedImageMessage && onUnlockImageMessage
+      ? () => onUnlockImageMessage(displayMessageId, remoteMessageId)
       : undefined;
 
   return (
@@ -93,7 +101,8 @@ export function MessageContent({
           {hasImage && imageUrl && (
             <ImageBubble
               characterId={characterId}
-              messageId={messageId}
+              displayMessageId={displayMessageId}
+              remoteMessageId={remoteMessageId}
               imageUrl={imageUrl}
               imagePaywalled={imagePaywalled}
               onOpenImage={onOpenImage}
@@ -102,7 +111,7 @@ export function MessageContent({
           {shouldRenderVoiceMessage ? (
             <VoiceBubble
               characterId={characterId}
-              messageId={messageId}
+              remoteMessageId={remoteMessageId}
               audioUrl={audioUrl}
               isFromAI={isFromAI}
               locked={isLockedVoiceMessage}
diff --git a/src/app/chat/components/voice-bubble.tsx b/src/app/chat/components/voice-bubble.tsx
index eb1aa33a..b86491ed 100644
--- a/src/app/chat/components/voice-bubble.tsx
+++ b/src/app/chat/components/voice-bubble.tsx
@@ -9,7 +9,7 @@ import styles from "./voice-bubble.module.css";
 
 export interface VoiceBubbleProps {
   characterId: string;
-  messageId?: string;
+  remoteMessageId?: string;
   audioUrl?: string | null;
   isFromAI: boolean;
   locked?: boolean;
@@ -20,7 +20,7 @@ export interface VoiceBubbleProps {
 
 export function VoiceBubble({
   characterId,
-  messageId,
+  remoteMessageId,
   audioUrl,
   isFromAI,
   locked = false,
@@ -36,7 +36,7 @@ export function VoiceBubble({
   const { mediaUrl, isUsingCachedMedia, reportMediaError } =
     useCachedChatMediaUrl({
       characterId,
-      messageId,
+      messageId: remoteMessageId,
       remoteUrl: audioUrl,
       kind: "audio",
     });
diff --git a/src/app/chat/hooks/use-chat-unlock-coordinator.ts b/src/app/chat/hooks/use-chat-unlock-coordinator.ts
index 85a15a3f..93c74b43 100644
--- a/src/app/chat/hooks/use-chat-unlock-coordinator.ts
+++ b/src/app/chat/hooks/use-chat-unlock-coordinator.ts
@@ -19,6 +19,7 @@ import {
 } from "@/stores/chat/chat-context";
 import type { ChatPromotionState } from "@/stores/chat/helper/promotion";
 import type { ChatUnlockPaywallRequest } from "@/stores/chat/chat-state";
+import type { UiMessage } from "@/stores/chat/ui-message";
 import { useUserSelector } from "@/stores/user/user-context";
 
 import { getInsufficientCreditsSubscriptionType } from "../chat-screen.helpers";
@@ -60,10 +61,11 @@ export interface UseChatUnlockCoordinatorInput
 }
 
 export interface UseChatUnlockCoordinatorOutput {
-  requestMessageUnlock: (
-    messageId: string,
-    kind: PendingChatUnlockKind,
-  ) => void;
+  requestMessageUnlock: (input: {
+    displayMessageId: string;
+    remoteMessageId?: string;
+    kind: PendingChatUnlockKind;
+  }) => void;
   dialogs: ChatUnlockDialogModel;
 }
 
@@ -81,6 +83,7 @@ export function useChatUnlockCoordinator({
     (state) => ({
       characterId: state.context.characterId,
       historyLoaded: state.context.historyLoaded,
+      messages: state.context.messages,
       isUnlockingHistory: state.matches({ userSession: "unlockingHistory" }),
       lockedHistoryCount: state.context.lockedHistoryCount,
       unlockHistoryError: state.context.unlockHistoryError,
@@ -141,10 +144,15 @@ export function useChatUnlockCoordinator({
 
       const consumed = await consumePendingChatUnlock(chatState.characterId);
       if (cancelled || !consumed) return;
+      const displayMessageId = resolvePendingUnlockDisplayMessageId(
+        consumed,
+        chatState.messages,
+        promotion,
+      );
 
       chatDispatch({
         type: "ChatUnlockMessageRequested",
-        messageId: consumed.displayMessageId,
+        displayMessageId,
         remoteMessageId: consumed.messageId,
         kind: consumed.kind,
         lockType: consumed.lockType,
@@ -165,14 +173,17 @@ export function useChatUnlockCoordinator({
     imageMessageId,
     imageReturnUrl,
     navigator.isAuthenticatedUser,
+    promotion,
+    chatState.messages,
   ]);
 
-  function requestMessageUnlock(
-    messageId: string,
-    kind: PendingChatUnlockKind,
-  ): void {
+  function requestMessageUnlock(input: {
+    displayMessageId: string;
+    remoteMessageId?: string;
+    kind: PendingChatUnlockKind;
+  }): void {
     const request = resolveMessageUnlockRequest(
-      { messageId, kind },
+      input,
       {
         defaultReturnUrl,
         imageMessageId,
@@ -186,7 +197,7 @@ export function useChatUnlockCoordinator({
       onAuthenticated: () => {
         chatDispatch({
           type: "ChatUnlockMessageRequested",
-          messageId: request.displayMessageId,
+          displayMessageId: request.displayMessageId,
           remoteMessageId: request.messageId,
           kind: request.kind,
           lockType: request.lockType,
@@ -258,23 +269,21 @@ export function useChatUnlockCoordinator({
 
 export function resolveMessageUnlockRequest(
   input: {
-    messageId: string;
+    displayMessageId: string;
+    remoteMessageId?: string;
     kind: PendingChatUnlockKind;
   },
   scope: ChatUnlockCoordinatorScope,
 ): CoordinatedMessageUnlockRequest {
   const matchedPromotion =
-    scope.promotion?.message.id === input.messageId
+    scope.promotion?.message.displayId === input.displayMessageId
       ? scope.promotion
       : null;
-  const temporaryPromotionMessageId = matchedPromotion
-    ? `promotion:${matchedPromotion.session.clientLockId}`
-    : null;
+  const remoteMessageId =
+    input.remoteMessageId ?? matchedPromotion?.message.remoteId;
   const target = {
-    displayMessageId: input.messageId,
-    ...(input.messageId !== temporaryPromotionMessageId
-      ? { messageId: input.messageId }
-      : {}),
+    displayMessageId: input.displayMessageId,
+    ...(remoteMessageId ? { messageId: remoteMessageId } : {}),
     kind: input.kind,
     ...(matchedPromotion
       ? {
@@ -300,6 +309,40 @@ export function shouldResumePendingChatUnlock(
   return isCurrentImageUnlock(pending, scope.imageMessageId);
 }
 
+export function resolvePendingUnlockDisplayMessageId(
+  pending: PendingChatUnlock,
+  messages: readonly UiMessage[],
+  promotion: ChatPromotionState | null,
+): string {
+  if (
+    promotion &&
+    (promotion.message.displayId === pending.displayMessageId ||
+      (pending.messageId &&
+        promotion.message.remoteId === pending.messageId))
+  ) {
+    return promotion.message.displayId;
+  }
+
+  const exactMessage = messages.find(
+    (message) => message.displayId === pending.displayMessageId,
+  );
+  if (exactMessage) return exactMessage.displayId;
+  if (!pending.messageId) return pending.displayMessageId;
+
+  const remoteMessage =
+    messages.find(
+      (message) =>
+        message.isFromAI &&
+        message.locked === true &&
+        message.remoteId === pending.messageId,
+    ) ??
+    messages.find(
+      (message) =>
+        message.isFromAI && message.remoteId === pending.messageId,
+    );
+  return remoteMessage?.displayId ?? pending.displayMessageId;
+}
+
 export function resolveChatUnlockReturnUrl(
   target: Pick<
     CoordinatedMessageUnlockRequest,
diff --git a/src/stores/chat/__tests__/chat-actor-cancellation.test.ts b/src/stores/chat/__tests__/chat-actor-cancellation.test.ts
index 953cfd07..f305f2a2 100644
--- a/src/stores/chat/__tests__/chat-actor-cancellation.test.ts
+++ b/src/stores/chat/__tests__/chat-actor-cancellation.test.ts
@@ -72,8 +72,8 @@ describe("chat actor request cancellation", () => {
     );
 
     const historyCall = historySync.syncNetworkHistory.mock.calls[0];
-    expect(historyCall?.[3]).toBe("Hello from Elio");
-    const signal = getSignal(historyCall?.[4]);
+    expect(historyCall?.[4]).toBe("Hello from Elio");
+    const signal = getSignal(historyCall?.[5]);
     expect(signal.aborted).toBe(false);
     actor.stop();
     expect(signal.aborted).toBe(true);
diff --git a/src/stores/chat/__tests__/chat-helpers.test.ts b/src/stores/chat/__tests__/chat-helpers.test.ts
index 561d901f..f0f0b4bf 100644
--- a/src/stores/chat/__tests__/chat-helpers.test.ts
+++ b/src/stores/chat/__tests__/chat-helpers.test.ts
@@ -6,6 +6,7 @@ import {
 } from "@/data/constants/character";
 import {
   ChatSendResponseSchema,
+  UnlockPrivateResponseSchema,
   type ChatSendResponse,
   type ChatSendResponseInput,
 } from "@/data/schemas/chat";
@@ -13,6 +14,7 @@ import type { ChatState } from "@/stores/chat/chat-state";
 import {
   applyHttpSendOutput,
   applyNetworkHistoryLoadedOutput,
+  applySingleUnlockOutput,
   countLockedHistoryMessages,
   localMessagesToUi,
   sendResponseToUiMessage,
@@ -178,6 +180,7 @@ describe("applyHttpSendOutput", () => {
     const context = makeChatState({
       messages: [
         {
+          displayId: "client:message:failed",
           content: "hello",
           isFromAI: false,
           date: "2026-06-25",
@@ -215,6 +218,7 @@ describe("applyHttpSendOutput", () => {
     const context = makeChatState({
       messages: [
         {
+          displayId: "client:message:successful",
           content: "hello",
           isFromAI: false,
           date: "2026-06-25",
@@ -257,6 +261,7 @@ describe("chat history pagination helpers", () => {
   it("falls back to the bounded history limit when the backend limit is zero", () => {
     const nextState = applyNetworkHistoryLoadedOutput(makeChatState(), {
       messages: [],
+      localDisplayIds: [],
       localCount: 0,
       total: 120,
       limit: 0,
@@ -266,9 +271,115 @@ describe("chat history pagination helpers", () => {
     expect(nextState.nextHistoryOffset).toBe(50);
     expect(nextState.historyTotal).toBe(120);
   });
+
+  it("preserves messages added after the local history snapshot", () => {
+    const localDisplayId = "server:history-1:assistant";
+    const optimisticMessage = {
+      displayId: "client:message:optimistic-1",
+      clientId: "optimistic-1",
+      content: "Sent while refreshing",
+      isFromAI: false,
+      date: "2026-07-20",
+    };
+    const nextState = applyNetworkHistoryLoadedOutput(
+      makeChatState({
+        messages: [
+          {
+            displayId: localDisplayId,
+            remoteId: "history-1",
+            content: "Cached",
+            isFromAI: true,
+            date: "2026-07-20",
+          },
+          optimisticMessage,
+        ],
+      }),
+      {
+        messages: [
+          {
+            displayId: localDisplayId,
+            remoteId: "history-1",
+            content: "Fresh",
+            isFromAI: true,
+            date: "2026-07-20",
+          },
+        ],
+        localDisplayIds: [localDisplayId],
+        localCount: 1,
+        total: 1,
+        limit: 50,
+      },
+    );
+
+    expect(nextState.messages).toEqual([
+      expect.objectContaining({
+        displayId: localDisplayId,
+        content: "Fresh",
+      }),
+      optimisticMessage,
+    ]);
+  });
 });
 
 describe("localMessagesToUi", () => {
+  it("uses distinct stable display ids for user and assistant records sharing a remote id", () => {
+    const records = [
+      {
+        id: "shared-1",
+        role: "user",
+        content: "Hello",
+        createdAt: "2026-06-25T12:00:00.000Z",
+      },
+      {
+        id: "shared-1",
+        role: "assistant",
+        content: "Hi",
+        createdAt: "2026-06-25T12:00:01.000Z",
+      },
+      {
+        id: "shared-1",
+        role: "assistant",
+        content: "A duplicated backend id",
+        createdAt: "2026-06-25T12:00:02.000Z",
+      },
+    ];
+
+    const first = localMessagesToUi(records);
+    const second = localMessagesToUi(records);
+
+    expect(first.map((message) => message.displayId)).toEqual([
+      "server:shared-1:user",
+      "server:shared-1:assistant",
+      "server:shared-1:assistant:1",
+    ]);
+    expect(first.map((message) => message.remoteId)).toEqual([
+      "shared-1",
+      "shared-1",
+      "shared-1",
+    ]);
+    expect(second.map((message) => message.displayId)).toEqual(
+      first.map((message) => message.displayId),
+    );
+  });
+
+  it("creates a stable legacy display id when history has no remote id", () => {
+    const records = [
+      {
+        role: "assistant",
+        type: "text",
+        content: "Legacy reply",
+        createdAt: "2026-06-25T12:00:00.000Z",
+      },
+    ];
+
+    const first = localMessagesToUi(records)[0];
+    const second = localMessagesToUi(records)[0];
+
+    expect(first?.displayId).toMatch(/^legacy:/);
+    expect(second?.displayId).toBe(first?.displayId);
+    expect(first?.remoteId).toBeUndefined();
+  });
+
   it("maps locked voice messages from history", () => {
     const [message] = localMessagesToUi([
       {
@@ -320,11 +431,53 @@ describe("localMessagesToUi", () => {
   });
 });
 
+describe("applySingleUnlockOutput", () => {
+  it("preserves display identity while adding the backend id", () => {
+    const displayId = "promotion:lock-1";
+    const [message] = applySingleUnlockOutput(
+      [
+        {
+          displayId,
+          content: "",
+          isFromAI: true,
+          date: "2026-07-20",
+          locked: true,
+          lockReason: "image_paywall",
+          imagePaywalled: true,
+        },
+      ],
+      {
+        displayMessageId: displayId,
+        request: {
+          displayMessageId: displayId,
+          lockType: "image_paywall",
+          clientLockId: "lock-1",
+        },
+        response: UnlockPrivateResponseSchema.parse({
+          unlocked: true,
+          messageId: "remote-1",
+          image: {
+            type: "promotion",
+            url: "https://example.com/unlocked.jpg",
+          },
+        }),
+      },
+    );
+
+    expect(message).toMatchObject({
+      displayId,
+      remoteId: "remote-1",
+      locked: false,
+    });
+  });
+});
+
 describe("countLockedHistoryMessages", () => {
   it("counts only unlockable locked AI messages", () => {
     expect(
       countLockedHistoryMessages([
         {
+          displayId: "private-1",
           content: "",
           isFromAI: true,
           date: "2026-06-29",
@@ -332,6 +485,7 @@ describe("countLockedHistoryMessages", () => {
           lockReason: "private_message",
         },
         {
+          displayId: "voice-1",
           content: "",
           isFromAI: true,
           date: "2026-06-29",
@@ -339,6 +493,7 @@ describe("countLockedHistoryMessages", () => {
           lockReason: "voice_message",
         },
         {
+          displayId: "image-1",
           content: "",
           isFromAI: true,
           date: "2026-06-29",
@@ -348,6 +503,7 @@ describe("countLockedHistoryMessages", () => {
           lockReason: "image",
         },
         {
+          displayId: "other-1",
           content: "",
           isFromAI: true,
           date: "2026-06-29",
@@ -355,6 +511,7 @@ describe("countLockedHistoryMessages", () => {
           lockReason: "insufficient_credits",
         },
         {
+          displayId: "user-1",
           content: "user text",
           isFromAI: false,
           date: "2026-06-29",
diff --git a/src/stores/chat/__tests__/chat-history-flow.test.ts b/src/stores/chat/__tests__/chat-history-flow.test.ts
index 865d962c..9b3bf6bc 100644
--- a/src/stores/chat/__tests__/chat-history-flow.test.ts
+++ b/src/stores/chat/__tests__/chat-history-flow.test.ts
@@ -38,13 +38,13 @@ describe("chat history flow", () => {
       resolveNetwork = resolve;
     });
     const localMessage: UiMessage = {
-      id: "local-msg",
+      displayId: "local-msg",
       content: "cached local message",
       isFromAI: true,
       date: "2026-07-02",
     };
     const networkMessage: UiMessage = {
-      id: "network-msg",
+      displayId: "network-msg",
       content: "fresh network message",
       isFromAI: true,
       date: "2026-07-02",
@@ -67,6 +67,7 @@ describe("chat history flow", () => {
               type: "ChatNetworkHistoryLoaded",
               output: {
                 messages: [networkMessage],
+                localDisplayIds: [localMessage.displayId],
                 localOverwritten: true,
                 localCount: 1,
                 networkCount: 1,
@@ -89,17 +90,17 @@ describe("chat history flow", () => {
     );
 
     expect(actor.getSnapshot().context.messages).toMatchObject([
-      { id: "local-msg", content: "cached local message" },
+      { displayId: "local-msg", content: "cached local message" },
     ]);
 
     resolveNetwork();
     await waitFor(
       actor,
-      (snapshot) => snapshot.context.messages[0]?.id === "network-msg",
+      (snapshot) => snapshot.context.messages[0]?.displayId === "network-msg",
     );
 
     expect(actor.getSnapshot().context.messages).toMatchObject([
-      { id: "network-msg", content: "fresh network message" },
+      { displayId: "network-msg", content: "fresh network message" },
     ]);
 
     actor.stop();
@@ -108,7 +109,7 @@ describe("chat history flow", () => {
   it("loads older pages until total is exhausted and keeps existing messages", async () => {
     const requests: LoadMoreHistoryActorEvent[] = [];
     const latestMessage: UiMessage = {
-      id: "latest",
+      displayId: "latest",
       content: "current unlocked message",
       isFromAI: true,
       date: "2026-07-15",
@@ -173,8 +174,8 @@ describe("chat history flow", () => {
     );
     expect(requests[0]).toMatchObject({ offset: 50, limit: 50 });
     expect(actor.getSnapshot().context.messages).toMatchObject([
-      { id: "older-50" },
-      { id: "latest", content: "current unlocked message" },
+      { displayId: "older-50" },
+      { displayId: "latest", content: "current unlocked message" },
     ]);
 
     actor.send({ type: "ChatLoadMoreHistoryRequested" });
@@ -290,10 +291,10 @@ describe("chat history flow", () => {
   });
 });
 
-function createHistoryMessage(id: string): UiMessage {
+function createHistoryMessage(displayId: string): UiMessage {
   return {
-    id,
-    content: `Message ${id}`,
+    displayId,
+    content: `Message ${displayId}`,
     isFromAI: true,
     date: "2026-07-15",
   };
diff --git a/src/stores/chat/__tests__/chat-machine.test-utils.ts b/src/stores/chat/__tests__/chat-machine.test-utils.ts
index 26182c9c..28de9833 100644
--- a/src/stores/chat/__tests__/chat-machine.test-utils.ts
+++ b/src/stores/chat/__tests__/chat-machine.test-utils.ts
@@ -170,6 +170,7 @@ export function createLoadHistoryCallback(
       type: "ChatNetworkHistoryLoaded",
       output: {
         messages: networkMessages,
+        localDisplayIds: messages.map((message) => message.displayId),
         localOverwritten: true,
         localCount: messages.length,
         networkCount: networkMessages.length,
diff --git a/src/stores/chat/__tests__/chat-promotion.test.ts b/src/stores/chat/__tests__/chat-promotion.test.ts
index f3f368b0..f5b6c1ac 100644
--- a/src/stores/chat/__tests__/chat-promotion.test.ts
+++ b/src/stores/chat/__tests__/chat-promotion.test.ts
@@ -22,7 +22,7 @@ describe("chat promotion", () => {
     const messages = appendPromotionMessage(
       [
         {
-          id: "history-1",
+          displayId: "history-1",
           content: "History",
           isFromAI: true,
           date: "2026-07-13",
@@ -31,7 +31,7 @@ describe("chat promotion", () => {
       state,
     );
 
-    expect(messages.map((message) => message.id)).toEqual([
+    expect(messages.map((message) => message.displayId)).toEqual([
       "history-1",
       "promotion:promotion-1",
     ]);
@@ -62,7 +62,8 @@ describe("chat promotion", () => {
     });
 
     expect(next?.message).toMatchObject({
-      id: "backend-1",
+      displayId: "promotion:promotion-1",
+      remoteId: "backend-1",
       imageUrl: "https://example.com/unlocked.jpg",
       imagePaywalled: false,
       locked: false,
@@ -71,10 +72,19 @@ describe("chat promotion", () => {
 
   it("keeps the promotion last and removes matching history duplicates", () => {
     const state = createChatPromotionState(promotion, "backend-1");
+    const userMessage = {
+      displayId: "server:backend-1:user",
+      remoteId: "backend-1",
+      content: "User message with the shared remote id",
+      isFromAI: false,
+      date: "2026-07-13",
+    };
     const messages = appendPromotionMessage(
       [
+        userMessage,
         {
-          id: "backend-1",
+          displayId: "server:backend-1:assistant",
+          remoteId: "backend-1",
           content: "Stale history copy",
           isFromAI: true,
           date: "2026-07-13",
@@ -83,6 +93,6 @@ describe("chat promotion", () => {
       state,
     );
 
-    expect(messages).toEqual([state.message]);
+    expect(messages).toEqual([userMessage, state.message]);
   });
 });
diff --git a/src/stores/chat/__tests__/chat-send-flow.test.ts b/src/stores/chat/__tests__/chat-send-flow.test.ts
index d60b2c25..3050e9e2 100644
--- a/src/stores/chat/__tests__/chat-send-flow.test.ts
+++ b/src/stores/chat/__tests__/chat-send-flow.test.ts
@@ -32,6 +32,10 @@ describe("chat send flow", () => {
       { content: "hello", isFromAI: false },
       { content: "still there?", isFromAI: false },
     ]);
+    for (const message of actor.getSnapshot().context.messages) {
+      expect(message.displayId).toMatch(/^client:message:/);
+      expect(message.clientId).toBeTruthy();
+    }
     expect(actor.getSnapshot().context.outgoingMessageRevision).toBe(2);
 
     actor.send({ type: "ChatSendMessage", content: "   " });
@@ -94,6 +98,9 @@ describe("chat send flow", () => {
       content: "[Image]",
       isFromAI: false,
     });
+    expect(
+      actor.getSnapshot().context.messages.at(-1)?.displayId,
+    ).toMatch(/^client:image:/);
     actor.stop();
   });
 
diff --git a/src/stores/chat/__tests__/chat-session-flow.test.ts b/src/stores/chat/__tests__/chat-session-flow.test.ts
index 74cb46fd..15db46a7 100644
--- a/src/stores/chat/__tests__/chat-session-flow.test.ts
+++ b/src/stores/chat/__tests__/chat-session-flow.test.ts
@@ -96,7 +96,7 @@ describe("chat session flow", () => {
       createTestChatMachine({
         historyMessages: [
           {
-            id: "history-1",
+            displayId: "history-1",
             content: "Existing history",
             isFromAI: true,
             date: "2026-07-13",
@@ -124,7 +124,7 @@ describe("chat session flow", () => {
     const context = actor.getSnapshot().context;
     expect(context.messages).toHaveLength(1);
     expect(context.promotion?.message).toMatchObject({
-      id: "promotion:promotion-1",
+      displayId: "promotion:promotion-1",
       locked: true,
       lockReason: "voice_message",
     });
diff --git a/src/stores/chat/__tests__/chat-unlock-flow.test.ts b/src/stores/chat/__tests__/chat-unlock-flow.test.ts
index f24c3b72..99a3c607 100644
--- a/src/stores/chat/__tests__/chat-unlock-flow.test.ts
+++ b/src/stores/chat/__tests__/chat-unlock-flow.test.ts
@@ -20,6 +20,7 @@ describe("chat unlock flow", () => {
       createTestChatMachine({
         historyMessages: [
           {
+            displayId: "private-1",
             content: "",
             isFromAI: true,
             date: "2026-06-29",
@@ -27,6 +28,7 @@ describe("chat unlock flow", () => {
             lockReason: "private_message",
           },
           {
+            displayId: "voice-1",
             content: "",
             isFromAI: true,
             date: "2026-06-29",
@@ -56,7 +58,7 @@ describe("chat unlock flow", () => {
       createTestChatMachine({
         historyMessages: [
           {
-            id: "msg-image-locked",
+            displayId: "msg-image-locked",
             content: "",
             isFromAI: true,
             date: "2026-06-29",
@@ -72,7 +74,7 @@ describe("chat unlock flow", () => {
           shortfallCredits: 0,
           messages: [
             {
-              id: "msg-image-locked",
+              displayId: "msg-image-locked",
               content: "",
               isFromAI: true,
               date: "2026-06-29",
@@ -97,7 +99,7 @@ describe("chat unlock flow", () => {
     expect(actor.getSnapshot().context.unlockHistoryPromptVisible).toBe(false);
     expect(actor.getSnapshot().context.messages).toMatchObject([
       {
-        id: "msg-image-locked",
+        displayId: "msg-image-locked",
         imageUrl: "https://example.com/locked.jpg",
         imagePaywalled: true,
         locked: true,
@@ -112,6 +114,7 @@ describe("chat unlock flow", () => {
       createTestChatMachine({
         historyMessages: [
           {
+            displayId: "private-1",
             content: "",
             isFromAI: true,
             date: "2026-06-29",
@@ -119,6 +122,7 @@ describe("chat unlock flow", () => {
             lockReason: "private_message",
           },
           {
+            displayId: "voice-1",
             content: "",
             isFromAI: true,
             date: "2026-06-29",
@@ -132,6 +136,7 @@ describe("chat unlock flow", () => {
           shortfallCredits: 0,
           messages: [
             {
+              displayId: "unlocked-1",
               content: "unlocked",
               isFromAI: true,
               date: "2026-06-29",
@@ -168,6 +173,7 @@ describe("chat unlock flow", () => {
       createTestChatMachine({
         historyMessages: [
           {
+            displayId: "private-1",
             content: "",
             isFromAI: true,
             date: "2026-06-29",
@@ -175,6 +181,7 @@ describe("chat unlock flow", () => {
             lockReason: "private_message",
           },
           {
+            displayId: "voice-1",
             content: "",
             isFromAI: true,
             date: "2026-06-29",
@@ -211,7 +218,7 @@ describe("chat unlock flow", () => {
       createTestChatMachine({
         historyMessages: [
           {
-            id: "msg-private-locked",
+            displayId: "msg-private-locked",
             content: "Original private message content.",
             isFromAI: true,
             date: "2026-06-29",
@@ -238,7 +245,8 @@ describe("chat unlock flow", () => {
 
     actor.send({
       type: "ChatUnlockMessageRequested",
-      messageId: "msg-private-locked",
+      displayMessageId: "msg-private-locked",
+      remoteMessageId: "msg-private-locked",
       kind: "private",
     });
 
@@ -250,7 +258,7 @@ describe("chat unlock flow", () => {
     expect(actor.getSnapshot().context.unlockingMessage).toBeNull();
     expect(actor.getSnapshot().context.messages).toMatchObject([
       {
-        id: "msg-private-locked",
+        displayId: "msg-private-locked",
         content: "Unlocked private message content.",
         locked: false,
         lockReason: null,
@@ -267,13 +275,15 @@ describe("chat unlock flow", () => {
       createTestChatMachine({
         historyMessages: [
           {
-            id: "msg-shared-id",
+            displayId: "server:msg-shared-id:user",
+            remoteId: "msg-shared-id",
             content: "User original question",
             isFromAI: false,
             date: "2026-06-29",
           },
           {
-            id: "msg-shared-id",
+            displayId: "server:msg-shared-id:assistant",
+            remoteId: "msg-shared-id",
             content: "Original AI private message",
             isFromAI: true,
             date: "2026-06-29",
@@ -300,7 +310,8 @@ describe("chat unlock flow", () => {
 
     actor.send({
       type: "ChatUnlockMessageRequested",
-      messageId: "msg-shared-id",
+      displayMessageId: "server:msg-shared-id:assistant",
+      remoteMessageId: "msg-shared-id",
       kind: "private",
     });
 
@@ -310,12 +321,14 @@ describe("chat unlock flow", () => {
 
     expect(actor.getSnapshot().context.messages).toMatchObject([
       {
-        id: "msg-shared-id",
+        displayId: "server:msg-shared-id:user",
+        remoteId: "msg-shared-id",
         content: "User original question",
         isFromAI: false,
       },
       {
-        id: "msg-shared-id",
+        displayId: "server:msg-shared-id:assistant",
+        remoteId: "msg-shared-id",
         content: "Unlocked private AI message.",
         isFromAI: true,
         locked: false,
@@ -333,7 +346,7 @@ describe("chat unlock flow", () => {
       createTestChatMachine({
         historyMessages: [
           {
-            id: "msg-image-locked",
+            displayId: "msg-image-locked",
             content: "",
             isFromAI: true,
             date: "2026-06-29",
@@ -360,7 +373,8 @@ describe("chat unlock flow", () => {
 
     actor.send({
       type: "ChatUnlockMessageRequested",
-      messageId: "msg-image-locked",
+      displayMessageId: "msg-image-locked",
+      remoteMessageId: "msg-image-locked",
       kind: "image",
     });
 
@@ -370,7 +384,7 @@ describe("chat unlock flow", () => {
 
     expect(actor.getSnapshot().context.messages).toMatchObject([
       {
-        id: "msg-image-locked",
+        displayId: "msg-image-locked",
         content: "",
         imageUrl: "https://example.com/locked.jpg",
         imagePaywalled: false,
@@ -387,7 +401,7 @@ describe("chat unlock flow", () => {
       createTestChatMachine({
         historyMessages: [
           {
-            id: "msg-voice-locked",
+            displayId: "msg-voice-locked",
             content: "Original voice transcript.",
             isFromAI: true,
             date: "2026-06-29",
@@ -414,7 +428,8 @@ describe("chat unlock flow", () => {
 
     actor.send({
       type: "ChatUnlockMessageRequested",
-      messageId: "msg-voice-locked",
+      displayMessageId: "msg-voice-locked",
+      remoteMessageId: "msg-voice-locked",
       kind: "voice",
     });
 
@@ -424,7 +439,7 @@ describe("chat unlock flow", () => {
 
     expect(actor.getSnapshot().context.messages).toMatchObject([
       {
-        id: "msg-voice-locked",
+        displayId: "msg-voice-locked",
         content: "Original voice transcript.",
         audioUrl: "https://example.com/unlocked-voice.mp3",
         locked: false,
@@ -441,7 +456,7 @@ describe("chat unlock flow", () => {
       createTestChatMachine({
         historyMessages: [
           {
-            id: "msg-voice-locked",
+            displayId: "msg-voice-locked",
             content: "",
             isFromAI: true,
             date: "2026-06-29",
@@ -473,7 +488,8 @@ describe("chat unlock flow", () => {
 
     actor.send({
       type: "ChatUnlockMessageRequested",
-      messageId: "msg-voice-locked",
+      displayMessageId: "msg-voice-locked",
+      remoteMessageId: "msg-voice-locked",
       kind: "voice",
     });
 
@@ -493,7 +509,7 @@ describe("chat unlock flow", () => {
     });
     expect(actor.getSnapshot().context.messages).toMatchObject([
       {
-        id: "msg-voice-locked",
+        displayId: "msg-voice-locked",
         locked: true,
         lockReason: "voice_message",
       },
@@ -509,7 +525,7 @@ describe("chat unlock flow", () => {
       createTestChatMachine({
         historyMessages: [
           {
-            id: "msg-missing",
+            displayId: "msg-missing",
             content: "",
             isFromAI: true,
             date: "2026-06-29",
@@ -541,7 +557,8 @@ describe("chat unlock flow", () => {
 
     actor.send({
       type: "ChatUnlockMessageRequested",
-      messageId: "msg-missing",
+      displayMessageId: "msg-missing",
+      remoteMessageId: "msg-missing",
       kind: "private",
     });
 
@@ -557,7 +574,7 @@ describe("chat unlock flow", () => {
     });
     expect(actor.getSnapshot().context.messages).toMatchObject([
       {
-        id: "msg-missing",
+        displayId: "msg-missing",
         locked: true,
         lockReason: "private_message",
       },
@@ -571,7 +588,7 @@ describe("chat unlock flow", () => {
       createTestChatMachine({
         historyMessages: [
           {
-            id: "msg-mismatch",
+            displayId: "msg-mismatch",
             content: "",
             isFromAI: true,
             date: "2026-07-20",
@@ -592,7 +609,8 @@ describe("chat unlock flow", () => {
     );
     actor.send({
       type: "ChatUnlockMessageRequested",
-      messageId: "msg-mismatch",
+      displayMessageId: "msg-mismatch",
+      remoteMessageId: "msg-mismatch",
       kind: "voice",
     });
     await waitFor(
@@ -617,7 +635,7 @@ describe("chat unlock flow", () => {
       resolveUnlock = resolve;
     });
     const originalMessage = {
-      id: "promotion:lock-1",
+      displayId: "promotion:lock-1",
       content: "",
       isFromAI: true,
       date: "2026-07-16",
@@ -648,7 +666,7 @@ describe("chat unlock flow", () => {
     );
     actor.send({
       type: "ChatUnlockMessageRequested",
-      messageId: "promotion:lock-1",
+      displayMessageId: "promotion:lock-1",
       remoteMessageId: "remote-1",
       kind: "image",
       lockType: "image_paywall",
@@ -669,6 +687,7 @@ describe("chat unlock flow", () => {
       type: "ChatNetworkHistoryLoaded",
       output: {
         messages: [],
+        localDisplayIds: [],
         localOverwritten: true,
         localCount: 0,
         networkCount: 0,
diff --git a/src/stores/chat/chat-events.ts b/src/stores/chat/chat-events.ts
index ff960b44..22b00285 100644
--- a/src/stores/chat/chat-events.ts
+++ b/src/stores/chat/chat-events.ts
@@ -51,7 +51,7 @@ export type ChatEvent =
   | { type: "ChatPromotionCleared" }
   | {
       type: "ChatUnlockMessageRequested";
-      messageId: string;
+      displayMessageId: string;
       remoteMessageId?: string;
       kind: PendingChatUnlockKind;
       lockType?: ChatLockType;
diff --git a/src/stores/chat/chat-history-sync.ts b/src/stores/chat/chat-history-sync.ts
index 0a78cfde..96290267 100644
--- a/src/stores/chat/chat-history-sync.ts
+++ b/src/stores/chat/chat-history-sync.ts
@@ -15,6 +15,8 @@ const log = new Logger("StoresChatChatHistorySync");
 export type ReadAndSyncHistoryOutput = {
   /** Network-authoritative messages. Empty network history includes a UI greeting. */
   messages: UiMessage[];
+  /** Display identities present in the local snapshot before the request. */
+  localDisplayIds: readonly string[];
   /** True when network history was written back to local storage. */
   localOverwritten: boolean;
   localCount: number;
@@ -31,8 +33,12 @@ export type LocalHistorySnapshotOutput = {
 
 export type NetworkHistorySyncOutput = ReadAndSyncHistoryOutput;
 
-export function createGreetingMessage(content: string): UiMessage {
+export function createGreetingMessage(
+  characterId: string,
+  content: string,
+): UiMessage {
   return {
+    displayId: `greeting:${encodeURIComponent(characterId)}`,
     content,
     isFromAI: true,
     date: todayString(),
@@ -49,10 +55,14 @@ export async function resolveHistoryCacheIdentity(
 
 export async function readLocalHistorySnapshot(
   cacheIdentity: string | null,
+  characterId: string,
   emptyChatGreeting: string,
 ): Promise<LocalHistorySnapshotOutput> {
   const chatRepo = await loadChatRepository();
-  const greetingMessage = createGreetingMessage(emptyChatGreeting);
+  const greetingMessage = createGreetingMessage(
+    characterId,
+    emptyChatGreeting,
+  );
 
   const localResult = cacheIdentity
     ? await chatRepo.getLocalMessages(cacheIdentity)
@@ -80,12 +90,16 @@ export async function readLocalHistorySnapshot(
 export async function syncNetworkHistory(
   characterId: string,
   localCount: number,
+  localDisplayIds: readonly string[],
   cacheIdentity: string | null,
   emptyChatGreeting: string,
   signal?: AbortSignal,
 ): Promise<NetworkHistorySyncOutput | null> {
   const chatRepo = await loadChatRepository();
-  const greetingMessage = createGreetingMessage(emptyChatGreeting);
+  const greetingMessage = createGreetingMessage(
+    characterId,
+    emptyChatGreeting,
+  );
 
   const networkResult = await chatRepo.getHistory(
     characterId,
@@ -134,6 +148,7 @@ export async function syncNetworkHistory(
 
   return {
     messages: finalMessages,
+    localDisplayIds,
     localOverwritten,
     localCount,
     networkCount: networkUi.length,
@@ -156,11 +171,13 @@ export async function readAndSyncHistory(
   const cacheIdentity = await resolveHistoryCacheIdentity(characterId);
   const localSnapshot = await readLocalHistorySnapshot(
     cacheIdentity,
+    characterId,
     emptyChatGreeting,
   );
   const networkSnapshot = await syncNetworkHistory(
     characterId,
     localSnapshot.localCount,
+    localSnapshot.messages.map((message) => message.displayId),
     cacheIdentity,
     emptyChatGreeting,
     signal,
@@ -169,6 +186,9 @@ export async function readAndSyncHistory(
 
   return {
     messages: localSnapshot.messages,
+    localDisplayIds: localSnapshot.messages.map(
+      (message) => message.displayId,
+    ),
     localOverwritten: false,
     localCount: localSnapshot.localCount,
     networkCount: 0,
diff --git a/src/stores/chat/helper/history.ts b/src/stores/chat/helper/history.ts
index dd2f0c1f..d61c3bdd 100644
--- a/src/stores/chat/helper/history.ts
+++ b/src/stores/chat/helper/history.ts
@@ -20,6 +20,7 @@ export function applyNetworkHistoryLoadedOutput(
   context: ChatState,
   output: {
     messages: UiMessage[];
+    localDisplayIds: readonly string[];
     localCount: number;
     total: number;
     limit: number;
@@ -33,8 +34,15 @@ export function applyNetworkHistoryLoadedOutput(
   | "nextHistoryOffset"
   | "isLoadingMoreHistory"
 > {
-  const localSnapshotSize = output.localCount === 0 ? 1 : output.localCount;
-  const optimisticTail = context.messages.slice(localSnapshotSize);
+  const localDisplayIds = new Set(output.localDisplayIds);
+  const networkDisplayIds = new Set(
+    output.messages.map((message) => message.displayId),
+  );
+  const optimisticTail = context.messages.filter(
+    (message) =>
+      !localDisplayIds.has(message.displayId) &&
+      !networkDisplayIds.has(message.displayId),
+  );
   const historyLimit = normalizeHistoryLimit(output.limit);
   return {
     messages: [...output.messages, ...optimisticTail],
@@ -95,13 +103,17 @@ export function prependUniqueHistoryMessages(
   olderMessages: readonly UiMessage[],
 ): UiMessage[] {
   const existingIds = new Set(
-    currentMessages.flatMap((message) => (message.id ? [message.id] : [])),
+    currentMessages.map((message) => message.displayId),
   );
   const pageIds = new Set<string>();
   const uniqueOlderMessages = olderMessages.filter((message) => {
-    if (!message.id) return true;
-    if (existingIds.has(message.id) || pageIds.has(message.id)) return false;
-    pageIds.add(message.id);
+    if (
+      existingIds.has(message.displayId) ||
+      pageIds.has(message.displayId)
+    ) {
+      return false;
+    }
+    pageIds.add(message.displayId);
     return true;
   });
   return [...uniqueOlderMessages, ...currentMessages];
diff --git a/src/stores/chat/helper/message-mappers.ts b/src/stores/chat/helper/message-mappers.ts
index fea786b7..367574c5 100644
--- a/src/stores/chat/helper/message-mappers.ts
+++ b/src/stores/chat/helper/message-mappers.ts
@@ -2,7 +2,12 @@ import type {
   ChatLockDetailData,
   ChatSendResponse,
 } from "@/data/schemas/chat";
-import type { UiMessage } from "@/stores/chat/ui-message";
+import {
+  createClientUiMessageIdentity,
+  createLegacyUiMessageIdentity,
+  createRemoteUiMessageIdentity,
+  type UiMessage,
+} from "@/stores/chat/ui-message";
 import { todayString } from "@/utils/date";
 
 /**
@@ -21,20 +26,33 @@ export function localMessagesToUi(
     lockDetail?: ChatLockDetailData;
   }[],
 ): UiMessage[] {
-  return records.map((m) => ({
-    ...(m.id ? { id: m.id } : {}),
-    content: getAiMessageDisplayContent({
-      content: m.content,
-      isFromAI: m.role === "assistant",
-      hasImage: Boolean(m.image?.url),
-    }),
-    isFromAI: m.role === "assistant",
-    date: messageDateFromCreatedAt(m.createdAt),
-    ...(m.audioUrl && m.lockDetail?.locked !== true
-      ? { audioUrl: m.audioUrl }
-      : {}),
-    ...deriveUiLockFields(m.lockDetail, m.image?.url),
-  }));
+  const occurrences = new Map<string, number>();
+  return records.map((m) => {
+    const isFromAI = m.role === "assistant";
+    const identityBase = m.id
+      ? `remote:${m.id}:${m.role}`
+      : `legacy:${createLegacyFingerprint(m)}`;
+    const occurrence = occurrences.get(identityBase) ?? 0;
+    occurrences.set(identityBase, occurrence + 1);
+    const identity = m.id
+      ? createRemoteUiMessageIdentity(m.id, isFromAI, occurrence)
+      : createLegacyUiMessageIdentity(identityBase, occurrence);
+
+    return {
+      ...identity,
+      content: getAiMessageDisplayContent({
+        content: m.content,
+        isFromAI,
+        hasImage: Boolean(m.image?.url),
+      }),
+      isFromAI,
+      date: messageDateFromCreatedAt(m.createdAt),
+      ...(m.audioUrl && m.lockDetail?.locked !== true
+        ? { audioUrl: m.audioUrl }
+        : {}),
+      ...deriveUiLockFields(m.lockDetail, m.image?.url),
+    };
+  });
 }
 
 /**
@@ -43,7 +61,9 @@ export function localMessagesToUi(
  */
 export function sendResponseToUiMessage(response: ChatSendResponse): UiMessage {
   return {
-    ...(response.messageId ? { id: response.messageId } : {}),
+    ...(response.messageId
+      ? createRemoteUiMessageIdentity(response.messageId, true)
+      : createClientUiMessageIdentity("reply")),
     content: getAiMessageDisplayContent({
       content: response.reply,
       isFromAI: true,
@@ -58,6 +78,28 @@ export function sendResponseToUiMessage(response: ChatSendResponse): UiMessage {
   };
 }
 
+function createLegacyFingerprint(record: {
+  type?: string;
+  content: string;
+  role: string;
+  createdAt: string;
+  audioUrl?: string | null;
+  image?: { type: string | null; url: string | null };
+  lockDetail?: ChatLockDetailData;
+}): string {
+  return JSON.stringify([
+    record.role,
+    record.type ?? "text",
+    record.content,
+    record.createdAt,
+    record.audioUrl ?? null,
+    record.image?.type ?? null,
+    record.image?.url ?? null,
+    record.lockDetail?.locked ?? null,
+    record.lockDetail?.reason ?? null,
+  ]);
+}
+
 function messageDateFromCreatedAt(createdAt: string): string {
   const parsed = new Date(createdAt);
   if (Number.isNaN(parsed.getTime())) return todayString();
diff --git a/src/stores/chat/helper/promotion.ts b/src/stores/chat/helper/promotion.ts
index 48c9277c..582fedff 100644
--- a/src/stores/chat/helper/promotion.ts
+++ b/src/stores/chat/helper/promotion.ts
@@ -28,7 +28,8 @@ export function createChatPromotionState(
   return {
     session,
     message: {
-      id: messageId || `promotion:${session.clientLockId}`,
+      displayId: `promotion:${session.clientLockId}`,
+      ...(messageId ? { remoteId: messageId } : {}),
       content: "",
       isFromAI: true,
       date: todayString(),
@@ -47,7 +48,13 @@ export function appendPromotionMessage(
 ): UiMessage[] {
   if (!promotion) return [...messages];
   return [
-    ...messages.filter((message) => message.id !== promotion.message.id),
+    ...messages.filter(
+      (message) =>
+        message.displayId !== promotion.message.displayId &&
+        (!promotion.message.remoteId ||
+          !message.isFromAI ||
+          message.remoteId !== promotion.message.remoteId),
+    ),
     promotion.message,
   ];
 }
@@ -56,7 +63,10 @@ export function applyPromotionUnlockOutput(
   promotion: ChatPromotionState | null,
   output: UnlockMessageOutput,
 ): ChatPromotionState | null {
-  if (!promotion || promotion.message.id !== output.displayMessageId) {
+  if (
+    !promotion ||
+    promotion.message.displayId !== output.displayMessageId
+  ) {
     return promotion;
   }
   return {
diff --git a/src/stores/chat/helper/unlock.ts b/src/stores/chat/helper/unlock.ts
index 9b9ec67a..60778e18 100644
--- a/src/stores/chat/helper/unlock.ts
+++ b/src/stores/chat/helper/unlock.ts
@@ -30,11 +30,11 @@ export function applySingleUnlockOutput(
       return message;
     }
 
-    const resolvedId = output.response.messageId || message.id;
+    const remoteId = output.response.messageId || message.remoteId;
     if (!output.response.unlocked) {
       return {
         ...message,
-        id: resolvedId,
+        ...(remoteId ? { remoteId } : {}),
       };
     }
 
@@ -47,7 +47,7 @@ export function applySingleUnlockOutput(
 
     return {
       ...message,
-      id: resolvedId,
+      ...(remoteId ? { remoteId } : {}),
       content: resolvedContent,
       audioUrl: getUnlockedAudioUrl(message, output.response),
       imageUrl: resolvedImageUrl,
@@ -69,8 +69,11 @@ function getUnlockedAudioUrl(
   return response.audioUrl;
 }
 
-function shouldApplySingleUnlock(message: UiMessage, messageId: string): boolean {
-  if (message.id !== messageId) return false;
+function shouldApplySingleUnlock(
+  message: UiMessage,
+  displayMessageId: string,
+): boolean {
+  if (message.displayId !== displayMessageId) return false;
   if (!message.isFromAI) return false;
   if (message.locked !== true) return false;
   return (
diff --git a/src/stores/chat/machine/actors/history.ts b/src/stores/chat/machine/actors/history.ts
index 02b2d78b..deb80e2b 100644
--- a/src/stores/chat/machine/actors/history.ts
+++ b/src/stores/chat/machine/actors/history.ts
@@ -46,6 +46,7 @@ export const loadHistoryActor = fromCallback<
     const cacheIdentity = await resolveHistoryCacheIdentity(input.characterId);
     const localSnapshot = await readLocalHistorySnapshot(
       cacheIdentity,
+      input.characterId,
       input.emptyChatGreeting,
     );
     if (cancelled) return;
@@ -57,6 +58,7 @@ export const loadHistoryActor = fromCallback<
     const networkSnapshot = await syncNetworkHistory(
       input.characterId,
       localSnapshot.localCount,
+      localSnapshot.messages.map((message) => message.displayId),
       cacheIdentity,
       input.emptyChatGreeting,
       controller.signal,
diff --git a/src/stores/chat/machine/send-flow.ts b/src/stores/chat/machine/send-flow.ts
index 1ae81a23..5c2a8552 100644
--- a/src/stores/chat/machine/send-flow.ts
+++ b/src/stores/chat/machine/send-flow.ts
@@ -9,6 +9,7 @@ import {
   finishPendingReply,
   type HttpSendOutput,
 } from "../helper/send-state";
+import { createClientUiMessageIdentity } from "../ui-message";
 import { historyMachineSetup } from "./history-flow";
 import { createChatActorActionSetup } from "./setup";
 
@@ -36,6 +37,7 @@ const appendGuestUserMessageAction = historyMachineSetup.assign(
       messages: [
         ...context.messages,
         {
+          ...createClientUiMessageIdentity("message"),
           content: event.content,
           isFromAI: false,
           date: today,
@@ -63,6 +65,7 @@ const appendUserMessageAction = historyMachineSetup.assign(
       messages: [
         ...context.messages,
         {
+          ...createClientUiMessageIdentity("message"),
           content: event.content,
           isFromAI: false,
           date: today,
@@ -83,6 +86,7 @@ const appendQueuedSendErrorMessageAction = historyMachineSetup.assign(
     const messages = [
       ...context.messages,
       {
+        ...createClientUiMessageIdentity("error"),
         content: unavailable
           ? "This character is temporarily unavailable. Please try again shortly."
           : "Something went wrong. Try sending again?",
@@ -135,6 +139,7 @@ const appendGuestUserImageAction = historyMachineSetup.assign(
       messages: [
         ...context.messages,
         {
+          ...createClientUiMessageIdentity("image"),
           content: "[Image]",
           isFromAI: false,
           date: today,
@@ -162,6 +167,7 @@ const appendUserImageAction = historyMachineSetup.assign(
       messages: [
         ...context.messages,
         {
+          ...createClientUiMessageIdentity("image"),
           content: "[Image]",
           isFromAI: false,
           date: today,
diff --git a/src/stores/chat/machine/session-flow.ts b/src/stores/chat/machine/session-flow.ts
index 1036247c..f21efdd0 100644
--- a/src/stores/chat/machine/session-flow.ts
+++ b/src/stores/chat/machine/session-flow.ts
@@ -157,7 +157,8 @@ const userReadyState = chatMachineSetup.createStateConfig({
       actions: "appendUserImage",
     },
     ChatUnlockMessageRequested: {
-      guard: ({ event }) => event.messageId.trim().length > 0,
+      guard: ({ event }) =>
+        event.displayMessageId.trim().length > 0,
       target: "unlockingMessage",
       actions: "markUnlockMessageStarted",
     },
diff --git a/src/stores/chat/machine/unlock-flow.ts b/src/stores/chat/machine/unlock-flow.ts
index 216f9a36..e25026d3 100644
--- a/src/stores/chat/machine/unlock-flow.ts
+++ b/src/stores/chat/machine/unlock-flow.ts
@@ -45,12 +45,12 @@ const markUnlockHistoryFailedAction = sendMachineSetup.assign(() => ({
 const markUnlockMessageStartedAction = sendMachineSetup.assign(
   ({ event }) => {
     if (event.type !== "ChatUnlockMessageRequested") return {};
-    const remoteMessageId =
-      event.remoteMessageId ?? (event.lockType ? undefined : event.messageId);
     return {
       unlockingMessage: {
-        displayMessageId: event.messageId,
-        ...(remoteMessageId ? { messageId: remoteMessageId } : {}),
+        displayMessageId: event.displayMessageId,
+        ...(event.remoteMessageId
+          ? { messageId: event.remoteMessageId }
+          : {}),
         kind: event.kind,
         ...(event.lockType ? { lockType: event.lockType } : {}),
         ...(event.clientLockId
@@ -90,8 +90,7 @@ const requestUnlockPaymentFromOutputAction = sendMachineSetup.assign(
       unlockMessageError: output.response.reason,
       unlockPaywallRequest: shouldOpenPaywall
         ? {
-            displayMessageId:
-              output.response.messageId || output.displayMessageId,
+            displayMessageId: output.displayMessageId,
             ...(output.response.messageId || output.request.messageId
               ? {
                   messageId:
@@ -105,7 +104,8 @@ const requestUnlockPaymentFromOutputAction = sendMachineSetup.assign(
             ...(output.request.clientLockId
               ? { clientLockId: output.request.clientLockId }
               : {}),
-            ...(context.promotion?.message.id === output.displayMessageId
+            ...(context.promotion?.message.displayId ===
+              output.displayMessageId
               ? { promotion: context.promotion.session }
               : {}),
             reason: output.response.reason,
@@ -130,7 +130,8 @@ const requestUnlockPaymentFromErrorAction = sendMachineSetup.assign(
       unlockPaywallRequest: request
         ? {
             ...request,
-            ...(context.promotion?.message.id === request.displayMessageId
+            ...(context.promotion?.message.displayId ===
+              request.displayMessageId
               ? { promotion: context.promotion.session }
               : {}),
             reason: "unlock_failed",
diff --git a/src/stores/chat/ui-message.ts b/src/stores/chat/ui-message.ts
index 7f95c714..ae8ef17d 100644
--- a/src/stores/chat/ui-message.ts
+++ b/src/stores/chat/ui-message.ts
@@ -1,7 +1,9 @@
 import { z } from "zod";
 
 export const UiMessageSchema = z.object({
-  id: z.string().optional(),
+  displayId: z.string().min(1),
+  remoteId: z.string().min(1).optional(),
+  clientId: z.string().min(1).optional(),
   content: z.string(),
   isFromAI: z.boolean(),
   date: z.string(),
@@ -18,6 +20,41 @@ export const UiMessageSchema = z.object({
 
 export type UiMessage = z.infer<typeof UiMessageSchema>;
 
+let fallbackClientId = 0;
+
+export function createRemoteUiMessageIdentity(
+  remoteId: string,
+  isFromAI: boolean,
+  occurrence = 0,
+): Pick<UiMessage, "displayId" | "remoteId"> {
+  const role = isFromAI ? "assistant" : "user";
+  const base = `server:${encodeURIComponent(remoteId)}:${role}`;
+  return {
+    displayId: occurrence > 0 ? `${base}:${occurrence}` : base,
+    remoteId,
+  };
+}
+
+export function createLegacyUiMessageIdentity(
+  fingerprint: string,
+  occurrence = 0,
+): Pick<UiMessage, "displayId"> {
+  const base = `legacy:${hashIdentity(fingerprint)}`;
+  return {
+    displayId: occurrence > 0 ? `${base}:${occurrence}` : base,
+  };
+}
+
+export function createClientUiMessageIdentity(
+  kind: "message" | "image" | "reply" | "error",
+): Pick<UiMessage, "displayId" | "clientId"> {
+  const clientId = createClientId();
+  return {
+    clientId,
+    displayId: `client:${kind}:${clientId}`,
+  };
+}
+
 export const UiMessage = {
   create(input: Omit<UiMessage, "date"> & { date?: string }): UiMessage {
     return UiMessageSchema.parse({
@@ -31,3 +68,20 @@ export const UiMessage = {
     });
   },
 };
+
+function createClientId(): string {
+  if (typeof globalThis.crypto?.randomUUID === "function") {
+    return globalThis.crypto.randomUUID();
+  }
+  fallbackClientId += 1;
+  return `${Date.now().toString(36)}-${fallbackClientId.toString(36)}`;
+}
+
+function hashIdentity(value: string): string {
+  let hash = 0x811c9dc5;
+  for (let index = 0; index < value.length; index += 1) {
+    hash ^= value.charCodeAt(index);
+    hash = Math.imul(hash, 0x01000193);
+  }
+  return (hash >>> 0).toString(36);
+}