diff --git a/par-api/src/main/java/com/par/api/controller/SnapshotController.java b/par-api/src/main/java/com/par/api/controller/SnapshotController.java
index b5bfeb1..d4ddef7 100644
--- a/par-api/src/main/java/com/par/api/controller/SnapshotController.java
+++ b/par-api/src/main/java/com/par/api/controller/SnapshotController.java
@@ -34,7 +34,7 @@ public class SnapshotController {
      * 获取站点当前生效配置快照（供 mediabot 使用）
      * 支持 ETag (If-None-Match) 实现增量更新
      * 优先从 Caffeine 缓存读取，缓存未命中查数据库并回退七牛云 CDN
-     * @param preview true=读取最新 draft（预览版），false/不传=读取最新 published（正式版）
+     * @param preview false/不传=仅正式版（published），true=预览版优先（draft → published fallback）
      */
     @GetMapping("/{siteId}")
     public ResponseEntity<?> getSnapshot(
@@ -44,7 +44,7 @@ public class SnapshotController {
 
         try {
             String bundleJson = preview
-                    ? snapshotService.getDraftBundleJson(siteId)
+                    ? snapshotService.getPreviewBundleJson(siteId)
                     : snapshotService.getActiveBundleJson(siteId);
 
             if (bundleJson == null || bundleJson.isEmpty()) {
diff --git a/par-core/src/main/java/com/par/core/service/SiteSnapshotService.java b/par-core/src/main/java/com/par/core/service/SiteSnapshotService.java
index 771f1e9..712022a 100644
--- a/par-core/src/main/java/com/par/core/service/SiteSnapshotService.java
+++ b/par-core/src/main/java/com/par/core/service/SiteSnapshotService.java
@@ -54,6 +54,14 @@ public interface SiteSnapshotService {
      */
     String getDraftBundleJson(String siteId);
 
+    /**
+     * 获取预览版快照 JSON（draft 优先，无 draft 时 fallback 到 published）
+     * 即：正式版 + 预览版 的并集
+     * @param siteId 站点标识
+     * @return JSON 字符串，空串表示无任何快照
+     */
+    String getPreviewBundleJson(String siteId);
+
     /**
      * 按 checksum 判断是否需要更新
      */
diff --git a/par-core/src/main/java/com/par/core/service/impl/SiteSnapshotServiceImpl.java b/par-core/src/main/java/com/par/core/service/impl/SiteSnapshotServiceImpl.java
index 3261d31..2f726f2 100644
--- a/par-core/src/main/java/com/par/core/service/impl/SiteSnapshotServiceImpl.java
+++ b/par-core/src/main/java/com/par/core/service/impl/SiteSnapshotServiceImpl.java
@@ -295,6 +295,16 @@ public class SiteSnapshotServiceImpl implements SiteSnapshotService {
         });
     }
 
+    @Override
+    public String getPreviewBundleJson(String siteId) {
+        // 先查 draft，有则返回；无则 fallback 到 published
+        String draftJson = getDraftBundleJson(siteId);
+        if (draftJson != null && !draftJson.isEmpty()) {
+            return draftJson;
+        }
+        return getActiveBundleJson(siteId);
+    }
+
     @Override
     public boolean isChanged(String siteId, String checksum) {
         if (checksum == null) return true;