fix: enforce SCADA chart device coverage

app/services/time_comparison_chart.py

@@ -13,7 +13,7 @@ DISPLAY_TIMEZONE = timezone(timedelta(hours=8))
 DAY_SECONDS = 86400
 
 
-def validate_time_comparison_chart(chart: Mapping[str, Any]) -> None:
+def validate_time_comparison_chart(chart: Mapping[str, Any], *, allow_missing_current: bool = False) -> None:
     """Validate new publications; persisted historical charts keep their read contract."""
     chart_type = chart["chart_type"]
     series = chart["series"]
@@ -70,8 +70,17 @@ def validate_time_comparison_chart(chart: Mapping[str, Any]) -> None:
             current_bases.update(bases)
         else:
             historical_bases.extend(bases)
-    check(len(current_bases) == 1, "当前 line 必须包含真实采样时间，且所有当前曲线使用同一窗口")
-    current = next(iter(current_bases))
+    scada = chart.get("scada")
+    empty_scada = allow_missing_current and not current_bases and scada and scada["role"] == "comparison"
+    check(len(current_bases) == 1 or bool(empty_scada),
+          "当前 line 必须包含真实采样时间，且所有当前曲线使用同一窗口")
+    # SCADA publication separately verifies every null against persisted reads.
+    if empty_scada:
+        window_start = datetime.fromisoformat(scada["window_start"]).astimezone(DISPLAY_TIMEZONE)
+        start_seconds = window_start.hour * 3600 + window_start.minute * 60 + window_start.second
+        current = window_start.replace(microsecond=0) + timedelta(seconds=(seconds[0] - start_seconds) % DAY_SECONDS)
+    else:
+        current = next(iter(current_bases))
     for historical in historical_bases:
         delta = (current - historical).total_seconds()
         check(delta > 0 and delta % DAY_SECONDS == 0,