feat: theme_line 取数升级,无评分命中时回退 theme_names

新增 _top_line: 优先评分最高主题,无命中时回退 _theme_clusters 的
主题名(非 markdown 示例),DAILY_WECOM_TOP_LINE=0 退回原逻辑。
复用现有 theme_line 行,不新增头部行(T5)。

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_top_line.py

@@ -0,0 +1,60 @@
+# tests/test_top_line.py
+"""T5: _top_line 看点行(theme_line 取数升级)测试。"""
+from __future__ import annotations
+
+import unittest
+from unittest import mock
+
+import daily.generate as g
+
+FEED_HIT = {
+    "topTrending": [
+        {"title": "remotion-video", "source": "src", "description": "video tool"},
+    ],
+    "topHot": [],
+}
+FEED_MISS = {
+    "topTrending": [
+        {"title": "zzz-nomatch", "source": "src", "description": "nothing"},
+    ],
+    "topHot": [],
+}
+
+
+class TopLineTests(unittest.TestCase):
+    def test_scores_hit_returns_theme(self):
+        # 命中 THEME_RULES(video) -> 评分最高主题
+        with mock.patch.object(g, "env_bool", return_value=True):
+            line = g._top_line(FEED_HIT)
+        self.assertIn("今日主题", line)
+        self.assertIn("AI 多媒体", line)
+
+    def test_fallback_to_theme_names_when_no_score(self):
+        # 无评分命中但 theme_clusters 能聚类 -> 用主题名
+        feed = {
+            "topTrending": [
+                {"id": "x", "title": "runcomfy-x", "source": "s", "description": "video x"},
+            ],
+            "topHot": [],
+        }
+        with mock.patch.object(g, "env_bool", return_value=True):
+            # 让评分落空(前 10 无命中)但 clusters(前 20)命中
+            line = g._top_line(feed)
+        self.assertIn("今日主题", line)
+        self.assertIn("AI 多媒体", line)
+
+    def test_switch_off_uses_legacy_detect(self):
+        # DAILY_WECOM_TOP_LINE=0 -> 退回 _detect_theme_line
+        with mock.patch.object(g, "env_bool", return_value=False):
+            line = g._top_line(FEED_MISS)
+        self.assertEqual(line, g._detect_theme_line(FEED_MISS))
+
+    def test_empty_feed_hardcoded_fallback(self):
+        # 完全无数据 -> 硬编码兜底, 不抛异常
+        with mock.patch.object(g, "env_bool", return_value=True):
+            line = g._top_line({"topTrending": [], "topHot": []})
+        self.assertIn("今日主题", line)
+
+
+if __name__ == "__main__":
+    unittest.main()