test(vfx #C.1.5a): real-emitter verification in OnRemove test + unused using

Code-review follow-up to 003c502:

1. Test 3 (OnRemove_StopsScriptsAndEmitters) now wires the runner into
   the real ParticleHookSink instead of a RecordingSink, registers a
   persistent EmitterDesc, lets the CreateParticleHook actually spawn an
   emitter, then asserts the sink killed it after OnRemove. Previously
   the test only verified runner-side state — sink.StopAllForEntity was
   never observably exercised, so a regression dropping that call would
   have passed silently.

2. Removed unused `using System.Numerics` from EntityScriptActivator.cs.

No production code changes. Tests 1 and 2 unchanged.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/AcDream.App/Rendering/Vfx/EntityScriptActivator.cs

@@ -1,5 +1,4 @@
 using System;
-using System.Numerics;
 using AcDream.Core.Vfx;
 using AcDream.Core.World;
 

tests/AcDream.Core.Tests/Rendering/Vfx/EntityScriptActivatorTests.cs

@@ -89,22 +89,64 @@ public sealed class EntityScriptActivatorTests
         Assert.Empty(p.Recording.Calls);
     }
 
+    /// <summary>
+    /// Persistent emitter: TotalDuration=0 and TotalParticles=0 prevent
+    /// auto-finish; InitialParticles=1 ensures a particle spawns at t=0
+    /// without waiting for the Birthrate timer; Lifespan=999f keeps that
+    /// particle alive far past the test horizon.
+    /// </summary>
+    private static EmitterDesc BuildPersistentEmitterDesc() => new()
+    {
+        DatId          = 100u,
+        Type           = ParticleType.Still,
+        EmitterKind    = ParticleEmitterKind.BirthratePerSec,
+        MaxParticles   = 4,
+        InitialParticles = 1,
+        TotalParticles = 0,   // 0 = no particle-count cap
+        TotalDuration  = 0f,  // 0 = no time-based finish
+        Lifespan       = 999f,
+        LifetimeMin    = 999f,
+        LifetimeMax    = 999f,
+        Birthrate      = 0.5f,
+        StartSize      = 0.5f,
+        EndSize        = 0.5f,
+        StartAlpha     = 1f,
+        EndAlpha       = 1f,
+    };
+
     [Fact]
     public void OnRemove_StopsScriptsAndEmitters()
     {
-        var p = BuildPipeline(
-            (0xAAu, BuildScript((0.0, new CreateParticleHook { EmitterInfoId = 100 }))));
-        var activator = new EntityScriptActivator(p.Runner, p.Sink, _ => 0xAAu);
+        // For this test we need the runner to dispatch into the REAL
+        // ParticleHookSink so OnRemove's sink.StopAllForEntity has a live
+        // emitter to kill. This is the only observable way to verify the
+        // call had effect without subclassing the sealed sink.
+        var registry = new EmitterDescRegistry();
+        registry.Register(BuildPersistentEmitterDesc());
+
+        var system  = new ParticleSystem(registry);
+        var hookSink = new ParticleHookSink(system);
+
+        var script = BuildScript((0.0, new CreateParticleHook { EmitterInfoId = 100u, Offset = new Frame() }));
+        var table  = new Dictionary<uint, DatPhysicsScript> { [0xAAu] = script };
+        var runner = new PhysicsScriptRunner(
+            id => table.TryGetValue(id, out var s) ? s : null,
+            hookSink);  // runner dispatches into real sink, not RecordingSink
+
+        var activator = new EntityScriptActivator(runner, hookSink, _ => 0xAAu);
         var entity = MakeEntity(serverGuid: 0xCAFEu, position: Vector3.Zero);
 
         activator.OnCreate(entity);
-        Assert.Equal(1, p.Runner.ActiveScriptCount);
+        runner.Tick(0.001f);  // fires the CreateParticleHook → spawns emitter
+
+        Assert.True(system.ActiveEmitterCount > 0,
+            "Setup precondition failed: emitter should be alive after the hook fires.");
 
         activator.OnRemove(0xCAFEu);
 
-        Assert.Equal(0, p.Runner.ActiveScriptCount);
-        // Tick after Remove must not surface any further hook fires.
-        p.Runner.Tick(1.0f);
-        Assert.Empty(p.Recording.Calls);
+        Assert.Equal(0, runner.ActiveScriptCount);
+        // sink.StopAllForEntity marks the emitter Finished; system.Tick reaps it.
+        system.Tick(0.01f);
+        Assert.Equal(0, system.ActiveEmitterCount);
     }
 }