fix(ai): 折叠态只显示一句话，那句话得说清是哪个指标

精简版的卡片正文就是第一条 highlight，标题不渲染。于是趋势页折叠起来是
「395 天内由 4376.0分 到 4905.0分（改善）」——什么的 4376 分？身体成分、
运动详情同样。

每个 builder 的第一条 detail 现在都自带主语，并加了不变量测试：detail 必须
包含它自己的 title（纯汇总性标题除外）。

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

backend/services/coach.py

@@ -495,6 +495,10 @@ def rule_scope_insight(context):
     return {
         # The first highlight leads and is then dropped from the list: showing
         # it in both places printed the same sentence twice.
+        #
+        # This is why every builder's first `detail` has to read on its own —
+        # here the `title` beside it is not rendered, and "395 天内由 4376 到
+        # 4905（改善）" without naming 耐力分 is a sentence about nothing.
         "headline": highlights[0]["detail"] if highlights else None,
         "points": [dict(h) for h in highlights[1:6]],
         "actions": [],

backend/services/scopes.py

@@ -280,7 +280,7 @@ def build_trends(user_id, subject=None):
     highlights = [{
         "title": t["label"],
         "detail": (
-            f"{t['days']} 天内由 {t['firstMean']}{t['unit']} 到 "
+            f"{t['label']} {t['days']} 天内由 {t['firstMean']}{t['unit']} 到 "
             f"{t['lastMean']}{t['unit']}（{t['direction']}），"
             f"斜率约 {t['slopePer30d']}{t['unit']}/30 天。"
         ),
@@ -332,7 +332,7 @@ def build_daily(user_id, subject=None):
         "detail": f"{d['label']} {d['value']}{d['unit']}，偏离基线 "
                   f"{abs(d['z']):.1f} 个标准差。",
     } for d in notable[:4]] or [
-        {"title": date, "detail": "这一天各项指标都在常态范围内。"}
+        {"title": date, "detail": f"{date} 各项指标都在常态范围内。"}
     ]
 
     return date, {
@@ -370,7 +370,8 @@ def build_body(user_id, subject=None):
                 continue
             highlights.append({
                 "title": label,
-                "detail": f"{first['date']} {a}{unit} → {last['date']} {b}{unit}"
+                "detail": f"{label}从 {first['date']} 的 {a}{unit} 到 "
+                          f"{last['date']} 的 {b}{unit}"
                           f"（{'+' if b >= a else ''}{round(b - a, 1)}{unit}）。",
             })
     elif series:
@@ -522,9 +523,11 @@ def build_activity(user_id, subject=None):
     total_zone = sum(z.get("seconds") or 0 for z in zones)
 
     minutes = round((base.get("duration") or summary.get("duration") or 0) / 60)
+    sport = (base.get("activity_type") or (detail or {}).get("activityType")
+             or "运动")
     highlights = [{
-        "title": base.get("activity_type") or (detail or {}).get("activityType") or "运动",
-        "detail": f"{minutes} 分钟"
+        "title": sport,
+        "detail": f"{sport} {minutes} 分钟"
                   + (f"，{round((base.get('distance') or 0) / 1000, 2)} km"
                      if base.get("distance") else "")
                   + (f"，平均心率 {base.get('heart_rate_average')}"

backend/tests/test_coach.py

@@ -1053,3 +1053,23 @@ class TestSupersede:
         statuses = {r["subject"]: r["status"] for r in analysis_svc.query_all(
             "SELECT subject, status FROM ai_jobs WHERE kind = 'trends'")}
         assert statuses.get("2026-08-01") == "running"
+
+
+class TestHighlightsReadAlone:
+    """The first highlight becomes the collapsed card's whole text, with no
+    title beside it — so it has to name what it is about."""
+
+    def test_every_first_highlight_names_its_subject(self, month):
+        for name in scopes.SCOPES:
+            built = scopes.build(month["id"], name)
+            if not built:
+                continue
+            first = built[1]["highlights"][0]
+            title = first["title"]
+            # Titles that are already summaries rather than names of a metric.
+            if title in ("整体", "当前预测") or title.startswith("近 "):
+                continue
+            assert title in first["detail"], (
+                f"{name}: 折叠态只显示 detail，但它没提到 {title!r}: "
+                f"{first['detail']!r}"
+            )