diff --git a/reaction_board/web/queries.py b/reaction_board/web/queries.py
index bea885a..0a08237 100644
--- a/reaction_board/web/queries.py
+++ b/reaction_board/web/queries.py
@@ -593,14 +593,15 @@ class DashboardQueries:
             items.sort(key=lambda item: item["aid"])
             items.sort(key=sort_key, reverse=True)
             total = len(items)
+            growth_available = any(
+                item.get("growth", {}).get("available") for item in items
+            )
             if not export:
                 start = (page - 1) * page_size
                 items = items[start:start + page_size]
             available = True
             reason = None
-            if sort in {"growth", "growth_rate"} and not any(
-                item.get("growth", {}).get("available") for item in items
-            ):
+            if sort in {"growth", "growth_rate"} and not growth_available:
                 available = False
                 reason = "需要至少两天的快照才能计算增长"
             return {
@@ -678,7 +679,12 @@ class DashboardQueries:
                     "points": [],
                     "available": False,
                 }
-            start = _date_minus(latest, days - 1) if days is not None else str(points[0]["stat_date"])
+            requested_start = (
+                _date_minus(latest, days - 1) if days is not None
+                else str(points[0]["stat_date"])
+            )
+            first_point = str(points[0]["stat_date"])
+            start = max(requested_start, first_point)
             dates = _date_range(start, latest)
             by_date = {str(point["stat_date"]): point for point in points}
             series: dict[str, list[int | None]] = {}
@@ -923,7 +929,8 @@ class DashboardQueries:
                     "days": days,
                 }
             latest = max(str(row["stat_date"]) for row in rows if int(row["ok"]) == 1) if any(int(row["ok"]) == 1 for row in rows) else str(rows[-1]["stat_date"])
-            start = _date_minus(latest, days - 1)
+            first_date = str(rows[0]["stat_date"])
+            start = max(_date_minus(latest, days - 1), first_date)
             dates = _date_range(start, latest)
             by_date = {str(row["stat_date"]): row for row in rows}
             series = []
@@ -1034,13 +1041,17 @@ class DashboardQueries:
                 "folder_sync": int(now + cfg.schedule.folder_sync_minutes * 60),
                 "snapshot": int(next_daily_run(now, cfg.schedule.snapshot_at)),
             }
-            for name, key in (("discover", "discover"), ("folder_sync", "folder_sync")):
+            for name, key, interval_minutes in (
+                ("discover", "discovery", cfg.schedule.discover_minutes),
+                ("folder_sync", "folder_sync", cfg.schedule.folder_sync_minutes),
+            ):
                 record = tasks.get(key)
                 if isinstance(record, dict) and record.get("finished_at"):
-                    next_runs[name] = int(record["finished_at"]) + (
-                        cfg.schedule.discover_minutes if name == "discover"
-                        else cfg.schedule.folder_sync_minutes
-                    ) * 60
+                    interval = int(interval_minutes) * 60
+                    candidate = int(record["finished_at"]) + interval
+                    while candidate <= now:
+                        candidate += interval
+                    next_runs[name] = candidate
             errors = [
                 {"task": name, **record}
                 for name, record in tasks.items()
diff --git a/reaction_board/web/server.py b/reaction_board/web/server.py
index 11b9a07..2cfd4aa 100644
--- a/reaction_board/web/server.py
+++ b/reaction_board/web/server.py
@@ -215,6 +215,7 @@ class DashboardHandler(BaseHTTPRequestHandler):
         html = """<!doctype html>
 <html lang="zh-CN"><head><meta charset="utf-8">
 <meta name="viewport" content="width=device-width,initial-scale=1">
+<link rel="icon" href="/static/favicon.svg" type="image/svg+xml">
 <title>登录 · Reaction 看板</title>
 <style>
 :root{color-scheme:light dark}body{margin:0;min-height:100vh;display:grid;
diff --git a/tests/test_cli.py b/tests/test_cli.py
index fd5805b..2a3b78e 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -194,6 +194,34 @@ def test_run_once_offline():
             db.close()
 
 
+def test_serve_preview_guard():
+    with tempfile.TemporaryDirectory() as tmp:
+        path = write_config(tmp)
+        assert run_cli(["init", "--config", str(path)])[0] == 0
+        db_path = Path(tmp) / "app.db"
+        try:
+            cli._assert_preview_database(db_path)
+        except cli.ConfigError as exc:
+            assert "preview:seeded" in str(exc)
+        else:
+            raise AssertionError("普通数据库不应通过 --preview 校验")
+
+        db = Database(db_path)
+        db.initialize()
+        try:
+            Repository(db).kv_set("preview:seeded", "1")
+        finally:
+            db.close()
+        cli._assert_preview_database(db_path)
+
+        try:
+            cli._assert_preview_database(Path(tmp) / "missing.db")
+        except cli.ConfigError as exc:
+            assert "不存在" in str(exc)
+        else:
+            raise AssertionError("缺失数据库应报错")
+
+
 def test_default_command_starts_web_and_scheduler():
     with tempfile.TemporaryDirectory() as tmp:
         path = write_config(tmp)
@@ -299,6 +327,7 @@ def main_test():
     test_auth_check_without_cookie()
     test_auth_check_all_and_auth_dispatch()
     test_run_once_offline()
+    test_serve_preview_guard()
     test_default_command_starts_web_and_scheduler()
     test_snapshot_backup_failure_returns_error_and_retries()
     test_candidates_and_discover_commands()
diff --git a/tests/test_preview_seed.py b/tests/test_preview_seed.py
index 737dab3..767fc31 100644
--- a/tests/test_preview_seed.py
+++ b/tests/test_preview_seed.py
@@ -203,6 +203,9 @@ def test_seed_preview_end_to_end():
             assert conn.execute(
                 "SELECT 1 FROM up_blacklist WHERE mid=?", (FAKE_BLACKLIST_MID,)
             ).fetchone() is not None
+            assert conn.execute(
+                "SELECT 1 FROM kv WHERE k='task:last:snapshot'"
+            ).fetchone() is not None
             up_rows = conn.execute(
                 "SELECT stat_date, follower FROM up_stat WHERE mid=37754047 "
                 "ORDER BY stat_date"
diff --git a/tests/test_web_queries.py b/tests/test_web_queries.py
index 77afa66..2f4a083 100644
--- a/tests/test_web_queries.py
+++ b/tests/test_web_queries.py
@@ -142,6 +142,10 @@ def test_video_detail_and_trend():
             assert trend["available"] is True
             assert len(trend["points"]) == 3
 
+            # 请求区间早于首次快照时，从首次快照开始，不制造空白历史
+            wide = q.video_trend(101, days=30)
+            assert wide["dates"] == list(DATES)
+
             # 删除中间一天，折线在缺失日期应为 None，而不是插值
             db.write(lambda conn: conn.execute(
                 "DELETE FROM snapshot WHERE aid=101 AND stat_date=?",
@@ -204,6 +208,8 @@ def test_fans_candidates_system_and_export():
             assert fans["delta_7d"] is None
             assert fans["delta_cum"] == 20
             assert fans["options"][0]["mid"] == 37754047
+            wide = q.fans(days=30)
+            assert wide["dates"] == list(DATES)
 
             candidates = q.candidates()
             assert candidates["total"] == 2
@@ -220,6 +226,8 @@ def test_fans_candidates_system_and_export():
             assert system["errors"] == []
             assert system["preview"] is False
             assert system["next_runs"]["snapshot"] > 0
+            assert system["next_runs"]["folder_sync"] > FIXED_NOW
+            assert system["next_runs"]["discover"] > FIXED_NOW
 
             exported = q.export_videos(sort="view")
             assert exported["total"] == 3
diff --git a/tests/test_web_server.py b/tests/test_web_server.py
index f5ed821..60d7611 100644
--- a/tests/test_web_server.py
+++ b/tests/test_web_server.py
@@ -74,6 +74,13 @@ def test_readonly_routes_and_static():
             assert "text/html" in headers["Content-Type"]
             assert b"<html" in payload.lower()
 
+            for asset in ("/static/style.css", "/static/app.js", "/static/vendor/echarts.min.js"):
+                status, asset_headers, asset_payload = running.request(asset)
+                assert status == 200, asset
+                assert asset_payload, asset
+                content_type = asset_headers["Content-Type"]
+                assert "text/css" in content_type or "javascript" in content_type, asset
+
             status, _, payload = running.request("/static/../config.json")
             assert status == 404
 
diff --git a/tools/seed_preview_db.py b/tools/seed_preview_db.py
index fffeaeb..96d6a53 100644
--- a/tools/seed_preview_db.py
+++ b/tools/seed_preview_db.py
@@ -254,6 +254,69 @@ def _insert_snapshot(
     )
 
 
+def _seed_task_records(conn: sqlite3.Connection, latest_day: date) -> None:
+    """写入可读的最近任务状态，让预览系统页有内容可看。"""
+    base = _timestamp(latest_day, hour=0, minute=1)
+    records = {
+        "snapshot": {
+            "name": "snapshot", "ok": True,
+            "started_at": int(base),
+            "finished_at": int(base + 1124),
+            "error": None,
+            "summary": {
+                "stat_date": latest_day.isoformat(), "total": 796, "ok": 796,
+                "failed": 0, "removed": 0, "completed": True,
+                "backup_path": f"data/backup/app-{latest_day.strftime('%Y%m%d')}.db",
+            },
+        },
+        "folder_sync": {
+            "name": "folder_sync", "ok": True,
+            "started_at": int(base + 20 * 3600),
+            "finished_at": int(base + 20 * 3600 + 8),
+            "error": None,
+            "summary": {"folders": 2, "added": 65, "removed": 0, "ok": True},
+        },
+        "discovery": {
+            "name": "discovery", "ok": True,
+            "started_at": int(base + 21 * 3600),
+            "finished_at": int(base + 21 * 3600 + 24),
+            "error": None,
+            "summary": {
+                "searches": 4, "items": 168, "candidates": 4,
+                "notified": 3, "errors": [],
+            },
+        },
+        "candidate_cleanup": {
+            "name": "candidate_cleanup", "ok": True,
+            "started_at": int(base + 22 * 3600),
+            "finished_at": int(base + 22 * 3600 + 1),
+            "error": None,
+            "summary": {"candidates_removed": 0, "fav_actions_expired": 0},
+        },
+    }
+    for name, record in records.items():
+        conn.execute(
+            "INSERT OR REPLACE INTO kv(k, v) VALUES (?, ?)",
+            (f"task:last:{name}", json.dumps(record, ensure_ascii=False)),
+        )
+    conn.execute(
+        "INSERT OR REPLACE INTO kv(k, v) VALUES ('snapshot:last_attempt', ?)",
+        (latest_day.isoformat(),),
+    )
+    conn.execute(
+        "INSERT OR REPLACE INTO kv(k, v) VALUES ('snapshot:last_completed', ?)",
+        (latest_day.isoformat(),),
+    )
+    conn.execute(
+        "INSERT OR REPLACE INTO kv(k, v) VALUES (?, '1')",
+        (f"snapshot:backup:{latest_day.isoformat()}",),
+    )
+    conn.execute(
+        "INSERT OR REPLACE INTO kv(k, v) VALUES (?, '')",
+        (f"snapshot:backup_error:{latest_day.isoformat()}",),
+    )
+
+
 def _seed_blacklist(conn: sqlite3.Connection, now: float) -> None:
     conn.execute(
         """
@@ -495,6 +558,7 @@ def seed_preview(
             up_rows = _seed_up_stats(conn, latest_day, days, anomaly_rng)
             _seed_candidates(conn, latest_day)
             _seed_blacklist(conn, _timestamp(latest_day, hour=14))
+            _seed_task_records(conn, latest_day)
         else:
             up_rows = 0
             conn.execute("DELETE FROM candidate WHERE channel = 'preview'")
@@ -635,6 +699,12 @@ def main(argv: Sequence[str] | None = None) -> int:
             config_out=args.config_out,
             with_anomalies=not args.no_anomalies,
         )
+    except PermissionError as exc:
+        print(json.dumps({
+            "ok": False,
+            "error": f"目标数据库被占用，请先停止预览服务: {exc}",
+        }, ensure_ascii=False))
+        return 2
     except (ValueError, FileNotFoundError, FileExistsError, RuntimeError, sqlite3.Error) as exc:
         print(json.dumps({"ok": False, "error": str(exc)}, ensure_ascii=False))
         return 2