diff --git a/src/app/chat/components/fullscreen-image-viewer.module.css b/src/app/chat/components/fullscreen-image-viewer.module.css
index 08aa5c9a..1fd61097 100644
--- a/src/app/chat/components/fullscreen-image-viewer.module.css
+++ b/src/app/chat/components/fullscreen-image-viewer.module.css
@@ -30,6 +30,13 @@
   transform: scale(1.08);
 }
 
+.nativePaywallImage {
+  position: absolute;
+  inset: 0;
+  width: 100%;
+  height: 100%;
+}
+
 .paywallScrim {
   position: absolute;
   inset: 0;
diff --git a/src/app/chat/components/fullscreen-image-viewer.tsx b/src/app/chat/components/fullscreen-image-viewer.tsx
index 3b4d8088..e0b861de 100644
--- a/src/app/chat/components/fullscreen-image-viewer.tsx
+++ b/src/app/chat/components/fullscreen-image-viewer.tsx
@@ -1,4 +1,5 @@
 "use client";
+/* eslint-disable @next/next/no-img-element */
 /**
  * FullscreenImageViewer 全屏图片查看器
  *
@@ -13,9 +14,11 @@ import { ChevronLeft } from "lucide-react";
 import Image from "next/image";
 import { useEffect } from "react";
 
+import { useCachedChatMediaUrl } from "../hooks/use-cached-chat-media-url";
 import styles from "./fullscreen-image-viewer.module.css";
 
 export interface FullscreenImageViewerProps {
+  messageId?: string;
   imageUrl: string;
   imagePaywalled?: boolean;
   onUnlockImagePaywall?: () => void;
@@ -23,11 +26,18 @@ export interface FullscreenImageViewerProps {
 }
 
 export function FullscreenImageViewer({
+  messageId,
   imageUrl,
   imagePaywalled = false,
   onUnlockImagePaywall,
   onClose,
 }: FullscreenImageViewerProps) {
+  const { mediaUrl } = useCachedChatMediaUrl({
+    messageId,
+    remoteUrl: imageUrl,
+    kind: "image",
+  });
+
   useEffect(() => {
     const handleKey = (e: KeyboardEvent) => {
       if (e.key === "Escape") onClose();
@@ -36,9 +46,13 @@ export function FullscreenImageViewer({
     return () => document.removeEventListener("keydown", handleKey);
   }, [onClose]);
 
-  const src = imageUrl.startsWith("data:") || imageUrl.startsWith("http")
-    ? imageUrl
-    : `data:image/png;base64,${imageUrl}`;
+  const sourceUrl = mediaUrl || imageUrl;
+  const src = sourceUrl.startsWith("data:") ||
+    sourceUrl.startsWith("http") ||
+    sourceUrl.startsWith("blob:")
+    ? sourceUrl
+    : `data:image/png;base64,${sourceUrl}`;
+  const shouldUseNativeImage = isBrowserLocalImageSrc(src);
 
   if (imagePaywalled) {
     return (
@@ -47,13 +61,21 @@ export function FullscreenImageViewer({
         role="dialog"
         aria-label="Locked fullscreen image"
       >
-        <Image
-          src={src}
-          alt=""
-          fill
-          sizes="(max-width: 540px) 100vw, 540px"
-          className={styles.paywallImage}
-        />
+        {shouldUseNativeImage ? (
+          <img
+            src={src}
+            alt=""
+            className={`${styles.nativePaywallImage} ${styles.paywallImage}`}
+          />
+        ) : (
+          <Image
+            src={src}
+            alt=""
+            fill
+            sizes="(max-width: 540px) 100vw, 540px"
+            className={styles.paywallImage}
+          />
+        )}
         <div className={styles.paywallScrim} aria-hidden="true" />
         <button
           type="button"
@@ -81,18 +103,35 @@ export function FullscreenImageViewer({
       role="dialog"
       aria-label="Fullscreen image"
     >
-      <Image
-        src={src}
-        alt=""
-        width={800}
-        height={800}
-        className={styles.viewerImage}
-        onError={(e) => {
-          (e.currentTarget as HTMLImageElement).style.display = "none";
-          (e.currentTarget.parentElement as HTMLElement).innerHTML =
-            '<div class="error">🖼</div>';
-        }}
-      />
+      {shouldUseNativeImage ? (
+        <img
+          src={src}
+          alt=""
+          className={styles.viewerImage}
+          onError={(e) => {
+            e.currentTarget.style.display = "none";
+            (e.currentTarget.parentElement as HTMLElement).innerHTML =
+              '<div class="error">🖼</div>';
+          }}
+        />
+      ) : (
+        <Image
+          src={src}
+          alt=""
+          width={800}
+          height={800}
+          className={styles.viewerImage}
+          onError={(e) => {
+            (e.currentTarget as HTMLImageElement).style.display = "none";
+            (e.currentTarget.parentElement as HTMLElement).innerHTML =
+              '<div class="error">🖼</div>';
+          }}
+        />
+      )}
     </div>
   );
 }
+
+function isBrowserLocalImageSrc(src: string): boolean {
+  return src.startsWith("blob:") || src.startsWith("data:");
+}
diff --git a/src/app/chat/components/image-bubble.tsx b/src/app/chat/components/image-bubble.tsx
index 8cf23a06..b650f8d7 100644
--- a/src/app/chat/components/image-bubble.tsx
+++ b/src/app/chat/components/image-bubble.tsx
@@ -1,4 +1,5 @@
 "use client";
+/* eslint-disable @next/next/no-img-element */
 /**
  * ImageBubble 图片气泡
  *
@@ -13,6 +14,7 @@ import { useState } from "react";
 
 import { ROUTE_BUILDERS } from "@/router/routes";
 
+import { useCachedChatMediaUrl } from "../hooks/use-cached-chat-media-url";
 import styles from "./image-bubble.module.css";
 
 export interface ImageBubbleProps {
@@ -28,9 +30,15 @@ export function ImageBubble({
 }: ImageBubbleProps) {
   const router = useRouter();
   const [error, setError] = useState(false);
+  const { mediaUrl } = useCachedChatMediaUrl({
+    messageId,
+    remoteUrl: imageUrl,
+    kind: "image",
+  });
 
-  const src = decodeBase64Image(imageUrl);
+  const src = decodeBase64Image(mediaUrl || imageUrl);
   const canOpen = Boolean(messageId);
+  const shouldUseNativeImage = isBrowserLocalImageSrc(src);
 
   const openImage = () => {
     if (!messageId) return;
@@ -54,6 +62,13 @@ export function ImageBubble({
     >
       {error ? (
         <div className={styles.errorFallback}>🖼</div>
+      ) : shouldUseNativeImage ? (
+        <img
+          className={styles.image}
+          src={src}
+          alt=""
+          onError={() => setError(true)}
+        />
       ) : (
         <Image
           className={styles.image}
@@ -80,3 +95,7 @@ function decodeBase64Image(uri: string): string {
   // 裸 base64 字符串 → 包装成 data URI（PNG 兜底）
   return `data:image/png;base64,${uri}`;
 }
+
+function isBrowserLocalImageSrc(src: string): boolean {
+  return src.startsWith("blob:") || src.startsWith("data:");
+}
diff --git a/src/app/chat/components/message-content.tsx b/src/app/chat/components/message-content.tsx
index 045acf02..c32e671f 100644
--- a/src/app/chat/components/message-content.tsx
+++ b/src/app/chat/components/message-content.tsx
@@ -73,6 +73,7 @@ export function MessageContent({
           )}
           {hasAudio && audioUrl ? (
             <VoiceBubble
+              messageId={messageId}
               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 fa71a0d0..de416a63 100644
--- a/src/app/chat/components/voice-bubble.tsx
+++ b/src/app/chat/components/voice-bubble.tsx
@@ -3,9 +3,11 @@
 import { LockKeyhole, Pause, Play } from "lucide-react";
 import { useEffect, useRef, useState } from "react";
 
+import { useCachedChatMediaUrl } from "../hooks/use-cached-chat-media-url";
 import styles from "./voice-bubble.module.css";
 
 export interface VoiceBubbleProps {
+  messageId?: string;
   audioUrl: string;
   isFromAI: boolean;
   locked?: boolean;
@@ -15,6 +17,7 @@ export interface VoiceBubbleProps {
 }
 
 export function VoiceBubble({
+  messageId,
   audioUrl,
   isFromAI,
   locked = false,
@@ -25,6 +28,11 @@ export function VoiceBubble({
   const audioRef = useRef<HTMLAudioElement>(null);
   const [isPlaying, setIsPlaying] = useState(false);
   const [hasError, setHasError] = useState(false);
+  const { mediaUrl } = useCachedChatMediaUrl({
+    messageId,
+    remoteUrl: audioUrl,
+    kind: "audio",
+  });
 
   useEffect(() => {
     const audio = audioRef.current;
@@ -117,7 +125,7 @@ export function VoiceBubble({
           </>
         ) : null}
       </div>
-      {!locked ? <audio ref={audioRef} src={audioUrl} preload="metadata" /> : null}
+      {!locked ? <audio ref={audioRef} src={mediaUrl} preload="metadata" /> : null}
     </div>
   );
 }
diff --git a/src/app/chat/hooks/use-cached-chat-media-url.ts b/src/app/chat/hooks/use-cached-chat-media-url.ts
new file mode 100644
index 00000000..f46d88a2
--- /dev/null
+++ b/src/app/chat/hooks/use-cached-chat-media-url.ts
@@ -0,0 +1,106 @@
+"use client";
+
+import { useEffect, useState } from "react";
+
+import type { LocalChatMediaKind } from "@/data/storage/chat";
+import { getChatRepository } from "@/data/repositories/chat_repository";
+import { Result } from "@/utils";
+
+export interface UseCachedChatMediaUrlInput {
+  messageId?: string | null;
+  remoteUrl?: string | null;
+  kind: LocalChatMediaKind;
+}
+
+export interface UseCachedChatMediaUrlOutput {
+  mediaUrl: string;
+  isUsingCachedMedia: boolean;
+}
+
+interface CachedMediaUrlState {
+  key: string;
+  objectUrl: string;
+}
+
+export function useCachedChatMediaUrl({
+  messageId,
+  remoteUrl,
+  kind,
+}: UseCachedChatMediaUrlInput): UseCachedChatMediaUrlOutput {
+  const [cachedState, setCachedState] = useState<CachedMediaUrlState | null>(
+    null,
+  );
+  const fallbackUrl = remoteUrl ?? "";
+  const stateKey =
+    messageId && remoteUrl ? `${messageId}:${kind}:${remoteUrl}` : "";
+
+  useEffect(() => {
+    if (!messageId || !remoteUrl || !isCacheableRemoteUrl(remoteUrl)) {
+      return;
+    }
+
+    let cancelled = false;
+    let objectUrl: string | null = null;
+
+    const applyBlob = (blob: Blob) => {
+      const nextObjectUrl = URL.createObjectURL(blob);
+      objectUrl = nextObjectUrl;
+      if (cancelled) {
+        URL.revokeObjectURL(nextObjectUrl);
+        return;
+      }
+      setCachedState((previous) => {
+        if (previous) URL.revokeObjectURL(previous.objectUrl);
+        return {
+          key: stateKey,
+          objectUrl: nextObjectUrl,
+        };
+      });
+    };
+
+    const resolveCachedMedia = async () => {
+      const chatRepo = getChatRepository();
+      const cachedResult = await chatRepo.getCachedMedia({ messageId, kind });
+      if (cancelled) return;
+
+      if (Result.isOk(cachedResult) && cachedResult.data) {
+        applyBlob(cachedResult.data.blob);
+        return;
+      }
+
+      const cacheResult = await chatRepo.cacheRemoteMedia({
+        messageId,
+        kind,
+        remoteUrl,
+      });
+      if (cancelled) return;
+
+      if (Result.isOk(cacheResult)) {
+        applyBlob(cacheResult.data.blob);
+      }
+    };
+
+    void resolveCachedMedia();
+
+    return () => {
+      cancelled = true;
+      if (objectUrl) URL.revokeObjectURL(objectUrl);
+    };
+  }, [kind, messageId, remoteUrl, stateKey]);
+
+  if (cachedState?.key === stateKey) {
+    return {
+      mediaUrl: cachedState.objectUrl,
+      isUsingCachedMedia: true,
+    };
+  }
+
+  return {
+    mediaUrl: fallbackUrl,
+    isUsingCachedMedia: false,
+  };
+}
+
+function isCacheableRemoteUrl(url: string): boolean {
+  return url.startsWith("http://") || url.startsWith("https://");
+}
diff --git a/src/app/chat/image/[messageId]/chat-image-viewer-screen.tsx b/src/app/chat/image/[messageId]/chat-image-viewer-screen.tsx
index cbf8d82b..069b4cac 100644
--- a/src/app/chat/image/[messageId]/chat-image-viewer-screen.tsx
+++ b/src/app/chat/image/[messageId]/chat-image-viewer-screen.tsx
@@ -76,6 +76,7 @@ export function ChatImageViewerScreen({
     <>
       <MobileShell background="#000000">
         <FullscreenImageViewer
+          messageId={messageId}
           imageUrl={message.imageUrl ?? ""}
           imagePaywalled={message.imagePaywalled === true}
           onUnlockImagePaywall={handleUnlockImagePaywall}
diff --git a/src/data/repositories/chat_repository.ts b/src/data/repositories/chat_repository.ts
index 991f5f25..49c23b7c 100644
--- a/src/data/repositories/chat_repository.ts
+++ b/src/data/repositories/chat_repository.ts
@@ -10,15 +10,30 @@ import {
   UnlockPrivateRequest,
   UnlockPrivateResponse,
 } from "@/data/dto/chat";
-import { Result } from "@/utils";
-import type { IChatRepository } from "@/data/repositories/interfaces";
-import { LocalChatStorage, LocalMessage } from "@/data/storage/chat";
+import { AuthStorage } from "@/data/storage/auth";
+import { UserStorage } from "@/data/storage/user/user_storage";
+import { Logger, Result } from "@/utils";
+import type {
+  CacheRemoteChatMediaInput,
+  ChatMediaLookupInput,
+  IChatRepository,
+} from "@/data/repositories/interfaces";
+import {
+  LocalChatMediaStorage,
+  LocalChatStorage,
+  LocalMessage,
+  type LocalChatMediaKind,
+  type LocalChatMediaRow,
+} from "@/data/storage/chat";
 import { createLazySingleton } from "./lazy_singleton";
 
+const log = new Logger("DataRepositoriesChatRepository");
+
 export class ChatRepository implements IChatRepository {
   constructor(
     private readonly api: ChatApi,
     private readonly localStorage: LocalChatStorage,
+    private readonly mediaStorage: LocalChatMediaStorage,
   ) {}
 
   // ============ 远程操作 ============
@@ -144,6 +159,92 @@ export class ChatRepository implements IChatRepository {
     return this._mapLocalStorageResult(this.localStorage.getMessageCount());
   }
 
+  // ============ 本地媒体缓存 ============
+
+  async getCachedMedia(
+    input: ChatMediaLookupInput,
+  ): Promise<Result<LocalChatMediaRow | null>> {
+    return Result.wrap(async () => {
+      const ownerKeys = await this._resolveMediaOwnerKeys();
+      for (const ownerKey of ownerKeys) {
+        const cacheKey = this._buildMediaCacheKey(ownerKey, input);
+        const result = await this.mediaStorage.getMedia(cacheKey);
+        if (Result.isErr(result)) throw result.error;
+        if (result.data) return result.data;
+      }
+      return null;
+    });
+  }
+
+  async cacheRemoteMedia(
+    input: CacheRemoteChatMediaInput,
+  ): Promise<Result<LocalChatMediaRow>> {
+    return Result.wrap(async () => {
+      if (!isCacheableRemoteUrl(input.remoteUrl)) {
+        throw new Error(`Unsupported media url: ${input.remoteUrl}`);
+      }
+
+      const ownerKeys = await this._resolveMediaOwnerKeys();
+      const ownerKey = ownerKeys[0] ?? "anonymous";
+      const cacheKey = this._buildMediaCacheKey(ownerKey, input);
+      for (const lookupOwnerKey of ownerKeys) {
+        const lookupCacheKey = this._buildMediaCacheKey(lookupOwnerKey, input);
+        const existingResult = await this.mediaStorage.getMedia(lookupCacheKey);
+        if (Result.isErr(existingResult)) throw existingResult.error;
+        if (existingResult.data) return existingResult.data;
+      }
+
+      const response = await fetch(input.remoteUrl, {
+        method: "GET",
+        cache: "force-cache",
+      });
+      if (!response.ok) {
+        throw new Error(
+          `Media download failed: ${response.status} ${response.statusText}`,
+        );
+      }
+
+      const blob = await response.blob();
+      if (blob.size <= 0) {
+        throw new Error("Media download returned an empty blob.");
+      }
+
+      const saveResult = await this.mediaStorage.saveMedia({
+        cacheKey,
+        ownerKey,
+        messageId: input.messageId,
+        kind: input.kind,
+        remoteUrl: input.remoteUrl,
+        blob,
+        mimeType:
+          blob.type || response.headers.get("content-type") || fallbackMimeType(input.kind),
+      });
+      if (Result.isErr(saveResult)) throw saveResult.error;
+      void requestPersistentStorage();
+
+      const savedResult = await this.mediaStorage.getMedia(cacheKey);
+      if (Result.isErr(savedResult)) throw savedResult.error;
+      if (!savedResult.data) {
+        throw new Error("Cached media could not be read after save.");
+      }
+      return savedResult.data;
+    });
+  }
+
+  async prefetchMediaForMessages(
+    messages: readonly ChatMessage[],
+  ): Promise<Result<void>> {
+    return this._prefetchMediaTargets(
+      messages.flatMap((message) => getMessageMediaTargets(message)),
+    );
+  }
+
+  async prefetchMediaForSendResponse(
+    response: ChatSendResponse,
+  ): Promise<Result<void>> {
+    return this._prefetchMediaTargets(getSendResponseMediaTargets(response));
+  }
+
   // ============ 私有助手 ============
 
   /** ChatMessage → LocalMessage：丢弃 wire 字段，注入 storage 层的 sessionId=""。 */
@@ -185,6 +286,55 @@ export class ChatRepository implements IChatRepository {
   ): Promise<Result<T>> {
     return await promise;
   }
+
+  private async _prefetchMediaTargets(
+    targets: readonly CacheRemoteChatMediaInput[],
+  ): Promise<Result<void>> {
+    return Result.wrap(async () => {
+      for (const target of uniqueMediaTargets(targets)) {
+        const result = await this.cacheRemoteMedia(target);
+        if (Result.isErr(result)) {
+          log.warn("[chat-media] prefetch failed", {
+            messageId: target.messageId,
+            kind: target.kind,
+            remoteUrl: target.remoteUrl,
+            error: result.error,
+          });
+        }
+      }
+    });
+  }
+
+  private async _resolveMediaOwnerKeys(): Promise<string[]> {
+    const ownerKeys: string[] = [];
+    const userIdResult = await UserStorage.getInstance().getUserId();
+    if (
+      Result.isOk(userIdResult) &&
+      userIdResult.data !== null &&
+      userIdResult.data.length > 0
+    ) {
+      ownerKeys.push(`user:${userIdResult.data}`);
+    }
+
+    const deviceIdResult = await AuthStorage.getInstance().getDeviceId();
+    if (
+      Result.isOk(deviceIdResult) &&
+      deviceIdResult.data !== null &&
+      deviceIdResult.data.length > 0
+    ) {
+      ownerKeys.push(`device:${deviceIdResult.data}`);
+    }
+
+    ownerKeys.push("anonymous");
+    return Array.from(new Set(ownerKeys));
+  }
+
+  private _buildMediaCacheKey(
+    ownerKey: string,
+    input: ChatMediaLookupInput,
+  ): string {
+    return `${ownerKey}:${input.messageId}:${input.kind}`;
+  }
 }
 
 /** 全局懒单例。 */
@@ -193,5 +343,93 @@ export const getChatRepository = createLazySingleton<IChatRepository>(
     new ChatRepository(
       chatApi,
       LocalChatStorage.getInstance(),
+      LocalChatMediaStorage.getInstance(),
     ),
 );
+
+function getMessageMediaTargets(
+  message: ChatMessage,
+): CacheRemoteChatMediaInput[] {
+  const targets: CacheRemoteChatMediaInput[] = [];
+  pushMediaTarget(targets, {
+    messageId: message.id,
+    kind: "image",
+    remoteUrl: message.image.url,
+  });
+  pushMediaTarget(targets, {
+    messageId: message.id,
+    kind: "audio",
+    remoteUrl: message.audioUrl,
+  });
+  return targets;
+}
+
+function getSendResponseMediaTargets(
+  response: ChatSendResponse,
+): CacheRemoteChatMediaInput[] {
+  const targets: CacheRemoteChatMediaInput[] = [];
+  pushMediaTarget(targets, {
+    messageId: response.messageId,
+    kind: "image",
+    remoteUrl: response.image.url,
+  });
+  pushMediaTarget(targets, {
+    messageId: response.messageId,
+    kind: "audio",
+    remoteUrl: response.audioUrl,
+  });
+  return targets;
+}
+
+function pushMediaTarget(
+  targets: CacheRemoteChatMediaInput[],
+  input: {
+    messageId: string;
+    kind: LocalChatMediaKind;
+    remoteUrl: string | null;
+  },
+): void {
+  if (input.messageId.length === 0) return;
+  if (!input.remoteUrl || !isCacheableRemoteUrl(input.remoteUrl)) return;
+  targets.push({
+    messageId: input.messageId,
+    kind: input.kind,
+    remoteUrl: input.remoteUrl,
+  });
+}
+
+function isCacheableRemoteUrl(url: string): boolean {
+  return url.startsWith("http://") || url.startsWith("https://");
+}
+
+function fallbackMimeType(kind: LocalChatMediaKind): string {
+  return kind === "image" ? "image/*" : "audio/mpeg";
+}
+
+function uniqueMediaTargets(
+  targets: readonly CacheRemoteChatMediaInput[],
+): CacheRemoteChatMediaInput[] {
+  const seen = new Set<string>();
+  return targets.filter((target) => {
+    const key = `${target.messageId}:${target.kind}:${target.remoteUrl}`;
+    if (seen.has(key)) return false;
+    seen.add(key);
+    return true;
+  });
+}
+
+let storagePersistenceRequested = false;
+
+async function requestPersistentStorage(): Promise<void> {
+  if (storagePersistenceRequested) return;
+  storagePersistenceRequested = true;
+  if (typeof navigator === "undefined") return;
+  if (!navigator.storage?.persist) return;
+
+  try {
+    const persisted = await navigator.storage.persist();
+    log.debug("[chat-media] persistent storage requested", { persisted });
+  } catch (error) {
+    log.debug("[chat-media] persistent storage request skipped", { error });
+  }
+}
diff --git a/src/data/repositories/interfaces/ichat_repository.ts b/src/data/repositories/interfaces/ichat_repository.ts
index 751ee67b..d1a7ce07 100644
--- a/src/data/repositories/interfaces/ichat_repository.ts
+++ b/src/data/repositories/interfaces/ichat_repository.ts
@@ -19,6 +19,19 @@ import type {
   UnlockHistoryResponse,
   UnlockPrivateResponse,
 } from "@/data/dto/chat";
+import type {
+  LocalChatMediaKind,
+  LocalChatMediaRow,
+} from "@/data/storage/chat";
+
+export interface ChatMediaLookupInput {
+  messageId: string;
+  kind: LocalChatMediaKind;
+}
+
+export interface CacheRemoteChatMediaInput extends ChatMediaLookupInput {
+  remoteUrl: string;
+}
 
 export interface IChatRepository {
   /** 发送一条消息。 */
@@ -58,4 +71,24 @@ export interface IChatRepository {
 
   /** 获取本地消息数量。 */
   getLocalMessageCount(): Promise<Result<number>>;
+
+  /** 获取本地缓存的图片 / 音频 Blob。 */
+  getCachedMedia(
+    input: ChatMediaLookupInput,
+  ): Promise<Result<LocalChatMediaRow | null>>;
+
+  /** 下载并缓存远程图片 / 音频 Blob。 */
+  cacheRemoteMedia(
+    input: CacheRemoteChatMediaInput,
+  ): Promise<Result<LocalChatMediaRow>>;
+
+  /** 后台预缓存历史消息中的图片 / 音频。失败不影响聊天主流程。 */
+  prefetchMediaForMessages(
+    messages: readonly ChatMessage[],
+  ): Promise<Result<void>>;
+
+  /** 后台预缓存发送响应中的图片 / 音频。失败不影响聊天主流程。 */
+  prefetchMediaForSendResponse(
+    response: ChatSendResponse,
+  ): Promise<Result<void>>;
 }
diff --git a/src/data/storage/chat/index.ts b/src/data/storage/chat/index.ts
index b1510796..1487b663 100644
--- a/src/data/storage/chat/index.ts
+++ b/src/data/storage/chat/index.ts
@@ -5,4 +5,5 @@
 export * from "./chat_storage";
 export * from "./local_chat_db";
 export * from "./local_chat_storage";
+export * from "./local_chat_media_storage";
 export * from "./local_message";
diff --git a/src/data/storage/chat/local_chat_db.ts b/src/data/storage/chat/local_chat_db.ts
index ad7dc626..e4e0c62c 100644
--- a/src/data/storage/chat/local_chat_db.ts
+++ b/src/data/storage/chat/local_chat_db.ts
@@ -32,13 +32,34 @@ export interface LocalMessageRow {
   sessionId: string;
 }
 
+export type LocalChatMediaKind = "image" | "audio";
+
+export interface LocalChatMediaRow {
+  cacheKey: string;
+  ownerKey: string;
+  messageId: string;
+  kind: LocalChatMediaKind;
+  remoteUrl: string;
+  blob: Blob;
+  mimeType: string;
+  byteSize: number;
+  createdAt: number;
+  updatedAt: number;
+  lastAccessedAt: number;
+}
+
 export class LocalChatDB extends Dexie {
   messages!: Table<LocalMessageRow, number>;
+  media!: Table<LocalChatMediaRow, string>;
 
   constructor(dbName: string = "cozsweet-chat") {
     super(dbName);
     this.version(1).stores({
       messages: "++dbId",
     });
+    this.version(2).stores({
+      messages: "++dbId",
+      media: "cacheKey, ownerKey, messageId, kind, remoteUrl, updatedAt, lastAccessedAt",
+    });
   }
 }
diff --git a/src/data/storage/chat/local_chat_media_storage.ts b/src/data/storage/chat/local_chat_media_storage.ts
new file mode 100644
index 00000000..f0c7f63f
--- /dev/null
+++ b/src/data/storage/chat/local_chat_media_storage.ts
@@ -0,0 +1,88 @@
+"use client";
+
+import { Result, type Result as ResultT } from "@/utils";
+
+import {
+  LocalChatDB,
+  type LocalChatMediaKind,
+  type LocalChatMediaRow,
+} from "./local_chat_db";
+
+export type { LocalChatMediaKind, LocalChatMediaRow };
+
+export interface SaveLocalChatMediaInput {
+  cacheKey: string;
+  ownerKey: string;
+  messageId: string;
+  kind: LocalChatMediaKind;
+  remoteUrl: string;
+  blob: Blob;
+  mimeType: string;
+}
+
+export class LocalChatMediaStorage {
+  private readonly db: LocalChatDB;
+  private static _instance: LocalChatMediaStorage | null = null;
+
+  constructor(db?: LocalChatDB) {
+    this.db = db ?? new LocalChatDB();
+  }
+
+  static getInstance(): LocalChatMediaStorage {
+    if (!LocalChatMediaStorage._instance) {
+      LocalChatMediaStorage._instance = new LocalChatMediaStorage();
+    }
+    return LocalChatMediaStorage._instance;
+  }
+
+  /** @internal */
+  static _resetForTests(): void {
+    LocalChatMediaStorage._instance = null;
+  }
+
+  async getMedia(cacheKey: string): Promise<ResultT<LocalChatMediaRow | null>> {
+    try {
+      const row = (await this.db.media.get(cacheKey)) ?? null;
+      if (row) {
+        await this.db.media.update(cacheKey, {
+          lastAccessedAt: Date.now(),
+        });
+      }
+      return Result.ok(row);
+    } catch (e) {
+      return Result.err(e);
+    }
+  }
+
+  async saveMedia(input: SaveLocalChatMediaInput): Promise<ResultT<void>> {
+    try {
+      const now = Date.now();
+      const existing = await this.db.media.get(input.cacheKey);
+      await this.db.media.put({
+        cacheKey: input.cacheKey,
+        ownerKey: input.ownerKey,
+        messageId: input.messageId,
+        kind: input.kind,
+        remoteUrl: input.remoteUrl,
+        blob: input.blob,
+        mimeType: input.mimeType,
+        byteSize: input.blob.size,
+        createdAt: existing?.createdAt ?? now,
+        updatedAt: now,
+        lastAccessedAt: now,
+      });
+      return Result.ok(undefined);
+    } catch (e) {
+      return Result.err(e);
+    }
+  }
+
+  async clearAll(): Promise<ResultT<void>> {
+    try {
+      await this.db.media.clear();
+      return Result.ok(undefined);
+    } catch (e) {
+      return Result.err(e);
+    }
+  }
+}
diff --git a/src/lib/auth/logout.ts b/src/lib/auth/logout.ts
deleted file mode 100644
index 92c3ac3f..00000000
--- a/src/lib/auth/logout.ts
+++ /dev/null
@@ -1,15 +0,0 @@
-"use client";
-/**
- * 登出（NextAuth 流程触发器）
- *
- * 调用 `signOut()` 清除 NextAuth session cookie 并重定向。
- * 不做任何持久化（不写 unstorage / 不调后端 / 不设自定义 cookie）。
- * 
- */
-import { signOut } from "next-auth/react";
-
-export class Logout {
-  async signOut(): Promise<void> {
-    await signOut();
-  }
-}
diff --git a/src/stores/chat/chat-machine.actors.ts b/src/stores/chat/chat-machine.actors.ts
index 31ba1648..2dc435ef 100644
--- a/src/stores/chat/chat-machine.actors.ts
+++ b/src/stores/chat/chat-machine.actors.ts
@@ -156,6 +156,7 @@ async function sendMessageViaHttp(content: string): Promise<{
     log.error("[chat-machine] sendMessageHttpActor failed", { error: result.error });
     throw result.error;
   }
+  void chatRepo.prefetchMediaForSendResponse(result.data);
   const isMessageLimit =
     result.data.lockDetail.locked &&
     result.data.lockDetail.showUpgrade &&
diff --git a/src/stores/chat/chat-machine.helpers.ts b/src/stores/chat/chat-machine.helpers.ts
index 5bc73a15..2c7b7f03 100644
--- a/src/stores/chat/chat-machine.helpers.ts
+++ b/src/stores/chat/chat-machine.helpers.ts
@@ -356,6 +356,7 @@ export async function readAndSyncHistory(): Promise<{
   log.debug("[chat-machine] loadHistory NETWORK DONE", {
     count: networkUi.length,
   });
+  void chatRepo.prefetchMediaForMessages(networkResult.data.messages);
 
   // 3. 用 network 覆盖 local
   const saveResult = await chatRepo.saveMessagesToLocal(networkResult.data.messages);