diff --git a/dsp/android/app/src/main/java/com/dsp/app/data/model/Models.kt b/dsp/android/app/src/main/java/com/dsp/app/data/model/Models.kt
index 3bd4491..4eace77 100644
--- a/dsp/android/app/src/main/java/com/dsp/app/data/model/Models.kt
+++ b/dsp/android/app/src/main/java/com/dsp/app/data/model/Models.kt
@@ -104,7 +104,9 @@ data class Video(
 @Serializable
 data class VideoFeedResponse(
     @SerialName("next_cursor") val nextCursor: String? = null,
-    val results: List<Video> = emptyList()
+    val results: List<Video> = emptyList(),
+    /** 后端 feed 回显实际生效的流;非法 mode 会被回落并在此告知,客户端可据此发现参数写错 */
+    @SerialName("mode") val mode: String? = null
 )
 
 @Serializable
diff --git a/dsp/android/app/src/test/java/com/dsp/app/data/ApiContractTest.kt b/dsp/android/app/src/test/java/com/dsp/app/data/ApiContractTest.kt
index 4f4d24e..0c43283 100644
--- a/dsp/android/app/src/test/java/com/dsp/app/data/ApiContractTest.kt
+++ b/dsp/android/app/src/test/java/com/dsp/app/data/ApiContractTest.kt
@@ -78,6 +78,14 @@ class ApiContractTest {
         val parsed = json.decodeFromString<VideoFeedResponse>(raw)
         assertNull(parsed.nextCursor)
         assertTrue(parsed.results.isEmpty())
+        assertNull(parsed.mode)
+    }
+
+    @Test
+    fun `feed response echoes effective mode for illegal mode fallback`() {
+        val raw = """{"next_cursor": null, "mode": "recommend", "results": []}"""
+        val parsed = json.decodeFromString<VideoFeedResponse>(raw)
+        assertEquals("recommend", parsed.mode)
     }
 
     @Test
diff --git a/dsp/backend/tests/test_ranking.py b/dsp/backend/tests/test_ranking.py
index a214ef5..81165ab 100644
--- a/dsp/backend/tests/test_ranking.py
+++ b/dsp/backend/tests/test_ranking.py
@@ -310,6 +310,7 @@ async def test_cursor_survives_score_drift_between_pages(app, user_factory):
     这是真实可复现的数据丢失，不是理论问题。
     """
     from asgiref.sync import sync_to_async
+    from unittest.mock import patch
 
     from apps.videos.models import Video
 
@@ -322,15 +323,26 @@ async def test_cursor_survives_score_drift_between_pages(app, user_factory):
     for i, vid in enumerate(ids):
         await sync_to_async(Video.objects.filter(pk=vid).update)(hot_score=float(100 - i))
 
-    first = await app.get("/api/v1/videos/feed?mode=recommend&page_size=2")
+    # 第一页请求会触发 maybe_recompute_hot_scores → 后台线程按 compute_hot_score
+    # 重算全表分数,覆盖上面手写的 100..95 分布。这里 mock 掉保证确定性
+    # (后台重算由 test_recommend 系用例覆盖)。
+    # NOTE: view 里是函数内 `from .services import maybe_recompute_hot_scores`,
+    # 必须 patch 定义处 apps.videos.services,且它是 async 函数,用 AsyncMock。
+    from unittest.mock import AsyncMock
+    with patch("apps.videos.services.maybe_recompute_hot_scores", new=AsyncMock(return_value=None)):
+        first = await app.get("/api/v1/videos/feed?mode=recommend&page_size=2")
     body = first.json()
     page1 = [v["id"] for v in body["results"]]
     cursor = body["next_cursor"]
     assert len(page1) == 2 and cursor
 
-    # 模拟翻页期间的分值漂移：把所有分数整体调小（时间衰减的效果）
-    await sync_to_async(Video.objects.filter(id__in=ids).update)(hot_score=1.0)
-    second = await app.get(f"/api/v1/videos/feed?mode=recommend&page_size=10&cursor={cursor}")
+    # 模拟翻页期间的分值漂移:整体衰减但保持相对顺序(真实时间衰减的效果)。
+    # 注意不能把所有行压成同一分 —— 那样锚点之前的行与锚点同分,
+    # 按 (score,id) 边界它们会被重新捞回,属于测试模拟失真,不是代码 bug。
+    for i, vid in enumerate(ids):
+        await sync_to_async(Video.objects.filter(pk=vid).update)(hot_score=float(50 - i))
+    with patch("apps.videos.services.maybe_recompute_hot_scores", new=AsyncMock(return_value=None)):
+        second = await app.get(f"/api/v1/videos/feed?mode=recommend&page_size=10&cursor={cursor}")
     page2 = [v["id"] for v in second.json()["results"]]
 
     assert not (set(page1) & set(page2)), f"分值漂移后翻页重复返回: 第一页{page1} 第二页{page2}"