measurement: record the start of adaptive probing as a rate change

backend/shared/MoShiro.Measurement/Blocks/BlockBase.cs

@@ -85,6 +85,7 @@ public abstract class BlockBase : IBlock
         }
 
         double max = Math.Max(Spec.Int("rate_max_hz"), Spec.Int("rate_min_hz"));
+        ReportStart(max);
         return new AdaptiveRate(new AdaptiveRateOptions
         {
             MinHz = Spec.Int("rate_min_hz"),
@@ -95,6 +96,22 @@ public abstract class BlockBase : IBlock
         });
     }
 
+    /// <summary>
+    /// 自适应开始：记一条「start → watch」（从最高频率起步）。审计据此知道这个任务从什么时候起在自适应，
+    /// 没有这条之前的时段是「没有记录」，不是某个状态。
+    /// </summary>
+    protected void ReportStart(double hz) =>
+        Env.OnRateChange?.Invoke(new RateChange
+        {
+            AtMs = Env.Time.GetUtcNow().ToUnixTimeMilliseconds(),
+            Task = Spec.Scope.Task?.Value,
+            Kind = Spec.KindId,
+            From = "start",
+            To = "watch",
+            Hz = Math.Round(hz, 3),
+            Reason = "start",
+        });
+
     private void LogTransition(ProbeTransition change)
     {
         Env.OnRateChange?.Invoke(new RateChange

backend/shared/MoShiro.Measurement/Blocks/Http.cs

@@ -143,6 +143,7 @@ public sealed class HttpDialer : BlockBase
         }
 
         double max = Math.Max(Spec.Int("rate_max_per_min"), Spec.Int("rate_min_per_min")) / 60.0;
+        ReportStart(max);
         return new AdaptiveRate(new AdaptiveRateOptions
         {
             MinHz = Spec.Int("rate_min_per_min") / 60.0,