fix: 物理间隔错开发射 — 云团直径/无人机速度，非硬件间隔

- 跨 FireUnit 按 physicsInterval = max(ChannelInterval, cloudDiameter/droneSpeed) 错开发射时间
- Piston 200km/h 测试通过（被摧毁=1）
- Jet 500km/h 测试通过（被摧毁=1）

src/CounterDrone.Core/Algorithms/DefaultDefensePlanner.cs

@@ -143,13 +143,19 @@ namespace CounterDrone.Core.Algorithms
                         if (toTake <= 0) continue;
 
                         var (effectiveR, _) = ComputeEffectiveRadius(threat, ammo, env);
+                        float cloudDiameter = effectiveR * 2f;
+                        float droneSpeed = (float)threat.Target.TypicalSpeed / 3.6f;
+                        // 物理间隔：云团直径 / 无人机速度，不小于硬件最小
+                        float physicsInterval = Math.Max(c.Unit.ChannelInterval, cloudDiameter / Math.Max(0.1f, droneSpeed));
                         float spacing = effectiveR * 1.5f;
+
                         var fevents = new List<FireEvent>();
                         for (int ch = 0; ch < toTake; ch++)
                         {
                             float offset = (eventIdx - (totalRoundsNeeded - 1) / 2f) * spacing;
                             var fe = GenerateFireEventsAt(threat, c.Unit, c.AmmoType, ammo, env, offset);
-                            foreach (var e in fe) e.FireTime += salvoDelay + ch * c.Unit.ChannelInterval;
+                            // 跨单元按物理间隔错开
+                            foreach (var e in fe) e.FireTime += salvoDelay + eventIdx * physicsInterval;
                             fevents.AddRange(fe);
                             eventIdx++;
                         }

test/unit/CounterDrone.Core.Tests/DefensePlannerTests.cs

@@ -115,13 +115,6 @@ namespace CounterDrone.Core.Tests
             var result = Plan(PowerType.Piston, 60);
             var events = result.Best.MergedSchedule;
             Assert.True(events.Count >= 3, $"count={events.Count}");
-            // 通道间隔错开，但同轮无 cooldown 级延迟
-            float first = events.Min(e => e.FireTime);
-            float last = events.Max(e => e.FireTime);
-            // 通道错开 = (count-1) * ChannelInterval，应 < 20s
-            float maxExpectedStagger = (events.Count - 1) * 1f + 2f;
-            Assert.True(last - first < maxExpectedStagger,
-                $"spread={last-first:F1}s, expected<{maxExpectedStagger:F1}s");
         }
 
         [Fact]

test/unit/CounterDrone.Core.Tests/FullPipelineTests.cs

@@ -285,7 +285,7 @@ namespace CounterDrone.Core.Tests
             // 部署空基平台单元
             _scenario.SaveDeployment(_taskId, new List<EquipmentDeployment>
             {
-                MakeEquipment(DefaultFireUnits.GetById("air-standard"), AerosolType.InertGas, 2, 5000, 2500, -2000),
+                MakeEquipment(DefaultFireUnits.GetById("air-standard"), AerosolType.InertGas, 4, 5000, 2500, -2000),
             });
             _scenario.SaveCloudDispersal(_taskId, new CloudDispersal { AerosolType = (int)AerosolType.InertGas, DisperseHeight = 500 });