fix: stabilize ai design history switching

electron/image-workspace/local-workspace.ts

@@ -257,6 +257,7 @@ const LOCAL_CAPABILITIES: DesignCapabilities = {
   image: true,
   video: true,
 };
+const LOCAL_CONVERSATION_MESSAGE_PAGE_SIZE = 10;
 
 type PersistedWorkspace = DesignWorkspaceSummary & {
   clientWorkspaceId: string;
@@ -542,9 +543,13 @@ export class LocalImageWorkspace implements DesignWorkspaceModule {
   async getConversation(
     workspaceId: string,
     conversationId: string,
+    before?: string,
   ): Promise<DesignConversation> {
     const state = await this.load();
-    return clone(this.requireConversation(state, workspaceId, conversationId));
+    return this.conversationView(
+      this.requireConversation(state, workspaceId, conversationId),
+      before,
+    );
   }
 
   renameWorkspace(input: DesignRenameWorkspaceInput): Promise<DesignWorkspace> {
@@ -1081,14 +1086,34 @@ export class LocalImageWorkspace implements DesignWorkspaceModule {
     });
   }
 
-  private conversationView(conversation: PersistedConversation): DesignConversation {
+  private conversationView(
+    conversation: PersistedConversation,
+    before?: string,
+  ): DesignConversation {
     const {
       clientConversationId: _clientId,
       requestHashes: _requestHashes,
       ...view
     } = conversation;
+    const endIndex = before === undefined
+      ? conversation.messages.length
+      : conversation.messages.findIndex((message) => message.id === before);
+    if (endIndex < 0) {
+      throw new LocalImageWorkspaceError(
+        422,
+        'conversation_history_cursor_invalid',
+        '历史会话分页位置已失效，请重新打开会话',
+      );
+    }
+    const startIndex = Math.max(0, endIndex - LOCAL_CONVERSATION_MESSAGE_PAGE_SIZE);
+    const messages = conversation.messages.slice(startIndex, endIndex);
     return clone({
       ...view,
+      messages,
+      messagePage: {
+        hasOlder: startIndex > 0,
+        nextBefore: startIndex > 0 ? messages[0]?.id ?? null : null,
+      },
       latestMessagePreview: latestMessagePreview(conversation.messages),
     });
   }