完善客户端模块与工作区能力

shared/image-workspace.ts

@@ -61,6 +61,8 @@ export type DesignConversationSummary = {
   conversationId: string;
   workspaceId: string;
   title: string;
+  /** A compact preview for history navigation; full messages are loaded on selection. */
+  latestMessagePreview?: string | null;
   turnRevision: number;
   phase: DesignWorkspacePhase;
   brief: DesignBrief;