feat(vfx #C.1.5a): add EntityScriptActivator (no wiring yet)

New ~50-line orchestrator that fires Setup.DefaultScript through the
already-shipped PhysicsScriptRunner on entity spawn and stops scripts +
live emitters on despawn. Resolver delegate avoids DatCollection coupling
so the class is fully unit-testable with stubs.

Three xUnit tests cover the three branches: fire-with-script,
no-op-without-script, stop-on-remove. No wiring into the live spawn path
yet -- that lands in the next commit.

Spec: docs/superpowers/specs/2026-05-12-phase-c1.5a-portals-design.md

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

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

@@ -0,0 +1,110 @@
+using System.Collections.Generic;
+using System.Numerics;
+using AcDream.App.Rendering.Vfx;
+using AcDream.Core.Physics;
+using AcDream.Core.Vfx;
+using AcDream.Core.World;
+using DatReaderWriter.Types;
+using Xunit;
+using DatPhysicsScript = DatReaderWriter.DBObjs.PhysicsScript;
+
+namespace AcDream.Core.Tests.Rendering.Vfx;
+
+public sealed class EntityScriptActivatorTests
+{
+    /// <summary>Recording sink so we can assert which hooks the runner fires.</summary>
+    private sealed class RecordingSink : IAnimationHookSink
+    {
+        public List<(uint EntityId, Vector3 Pos, AnimationHook Hook)> Calls = new();
+        public void OnHook(uint entityId, Vector3 worldPos, AnimationHook hook)
+            => Calls.Add((entityId, worldPos, hook));
+    }
+
+    private static DatPhysicsScript BuildScript(params (double time, AnimationHook hook)[] items)
+    {
+        var script = new DatPhysicsScript();
+        foreach (var (t, h) in items)
+            script.ScriptData.Add(new PhysicsScriptData { StartTime = t, Hook = h });
+        return script;
+    }
+
+    private static WorldEntity MakeEntity(uint serverGuid, Vector3 position) =>
+        new()
+        {
+            Id = serverGuid,
+            ServerGuid = serverGuid,
+            SourceGfxObjOrSetupId = 0x02000001u,
+            Position = position,
+            Rotation = Quaternion.Identity,
+            MeshRefs = System.Array.Empty<MeshRef>(),
+        };
+
+    private record Pipeline(
+        ParticleSystem System,
+        ParticleHookSink Sink,
+        PhysicsScriptRunner Runner,
+        RecordingSink Recording);
+
+    private static Pipeline BuildPipeline(params (uint id, DatPhysicsScript script)[] scripts)
+    {
+        var registry = new EmitterDescRegistry();
+        var system = new ParticleSystem(registry);
+        var hookSink = new ParticleHookSink(system);          // for activator's StopAllForEntity
+        var recording = new RecordingSink();                  // for runner's hook dispatch
+        var table = new Dictionary<uint, DatPhysicsScript>();
+        foreach (var (id, s) in scripts) table[id] = s;
+        var runner = new PhysicsScriptRunner(
+            id => table.TryGetValue(id, out var s) ? s : null,
+            recording);
+        return new Pipeline(system, hookSink, runner, recording);
+    }
+
+    [Fact]
+    public void OnCreate_WithDefaultScript_FiresRunnerWithEntityGuidAndPosition()
+    {
+        var p = BuildPipeline(
+            (0xAAu, BuildScript((0.0, new CreateParticleHook { EmitterInfoId = 100 }))));
+        var activator = new EntityScriptActivator(p.Runner, p.Sink, _ => 0xAAu);
+        var entity = MakeEntity(serverGuid: 0xCAFEu, position: new Vector3(1, 2, 3));
+
+        activator.OnCreate(entity);
+
+        Assert.Equal(1, p.Runner.ActiveScriptCount);
+        p.Runner.Tick(0.001f);
+        Assert.Single(p.Recording.Calls);
+        Assert.Equal(0xCAFEu, p.Recording.Calls[0].EntityId);
+        Assert.Equal(new Vector3(1, 2, 3), p.Recording.Calls[0].Pos);
+    }
+
+    [Fact]
+    public void OnCreate_WithoutDefaultScript_DoesNothing()
+    {
+        var p = BuildPipeline();   // no scripts registered
+        var activator = new EntityScriptActivator(p.Runner, p.Sink, _ => 0u);
+        var entity = MakeEntity(serverGuid: 0xCAFEu, position: Vector3.Zero);
+
+        activator.OnCreate(entity);
+
+        Assert.Equal(0, p.Runner.ActiveScriptCount);
+        Assert.Empty(p.Recording.Calls);
+    }
+
+    [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);
+        var entity = MakeEntity(serverGuid: 0xCAFEu, position: Vector3.Zero);
+
+        activator.OnCreate(entity);
+        Assert.Equal(1, p.Runner.ActiveScriptCount);
+
+        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);
+    }
+}