fix(api): never cache anchor=latest windows as immutable [CI]

backend/src/MoShiro.Backend.Api/Common/QueryHelpers.cs

@@ -32,7 +32,10 @@ internal static class QueryHelpers
     /// </summary>
     public static IResult? ApplyCaching(HttpContext http, QueryRange range, long nowMs, string material)
     {
-        bool closed = !range.IsRelative && range.RequestedToMs < nowMs - (2 * Steps.Minute);
+        // anchor=latest 的相对时间段会被换成以“最后一个样本”为终点的绝对区间：线路停过一阵再恢复时，同一个地址的内容就会变，
+        // 不能当成“已经结束的区间”永久缓存（浏览器会把某一刻的旧数据一直留着，页面上就是线路条不更新）。
+        bool anchored = string.Equals(http.Request.Query["anchor"], "latest", StringComparison.OrdinalIgnoreCase);
+        bool closed = !anchored && !range.IsRelative && range.RequestedToMs < nowMs - (2 * Steps.Minute);
         if (!closed)
         {
             http.Response.Headers.CacheControl = "no-store";

backend/tests/MoShiro.Backend.Tests/IngestAndQueryTests.cs

@@ -96,6 +96,10 @@ public sealed class IngestAndQueryTests : IClassFixture<BackendFixture>
             Assert.Equal(600, anchored["summary"]!["samples"]!["udp_echo"]!.GetValue<long>());
             Assert.False(anchored["live"]!.GetValue<bool>());
 
+            // 这个窗口是以“最后一个样本”为终点的绝对区间，但线路恢复之后同一个地址的内容就变了：不能被浏览器永久缓存
+            using HttpResponseMessage raw = await _backend.Admin.GetAsync($"/api/public/lines/{_backend.Line(id)}/series?range=5m&step=10s&metrics=loss.total&anchor=latest");
+            Assert.Equal("no-store", raw.Headers.CacheControl!.ToString());
+
             // anchor=now is the default behaviour; anything else is rejected
             JsonNode explicitNow = await SeriesAsync(id, "range=5m&step=10s&metrics=loss.total&anchor=now");
             Assert.Null(explicitNow["summary"]!["samples"]!["udp_echo"]);