weather(phase-6bc): wire PlayScript packet + script runner into frame loop

Phase 6b — WorldSession now dispatches the PlayScript opcode (0xF754)
that retail uses for all server-triggered client-side visual effects.
Wire format per Agent #5 decompile (chunk_006A0000.c:12320-12336):

    [u32 opcode=0xF754][u32 targetGuid][u32 scriptId]

New event `PlayScriptReceived(uint guid, uint scriptId)` fires on
every matching fragment. Unknown payloads (body < 12 bytes) are
silently ignored.

Phase 6c — GameWindow instantiates a PhysicsScriptRunner at startup,
subscribes to PlayScriptReceived, and ticks the runner every frame
BEFORE the ParticleSystem tick so a CreateParticleHook fired this
frame gets its emitter integrated in the same frame.

Anchor policy: use the camera's world position for the script anchor.
For Dereth-wide storm effects (lightning flashes) the camera is the
right reference frame — the flash is "around the player." Per-entity
effects (spell casts, emotes) dedupe by (scriptId, entityId) so
multiple simultaneous plays on different guids work; a follow-up will
look up the guid's last-known world pos from _worldState for accurate
per-entity anchoring.

The full pipeline now for a lightning flash:
  1. ACE (or other retail-emulating server) sends
     GameMessage(0xF754, lightningGuid, scriptId=0x33xxxxxx).
  2. WorldSession parses: PlayScriptReceived event fires.
  3. GameWindow.OnPlayScriptReceived routes to _scriptRunner.Play.
  4. Runner loads the PhysicsScript from the dat, schedules every
     (StartTime, AnimationHook) entry.
  5. Per-frame Tick fires each hook at its scheduled time via
     ParticleHookSink — CreateParticleHook spawns a particle emitter
     (the flash), SoundHook plays thunder audio (Phase 5d), etc.

Set ACDREAM_DUMP_PLAYSCRIPT=1 to see each inbound PlayScript and each
hook fire as `[pes]` log lines — useful for identifying which script
IDs your ACE server actually sends.

Build + 742 tests green.

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

src/AcDream.App/Rendering/GameWindow.cs

@@ -140,6 +140,10 @@ public sealed class GameWindow : IDisposable
     private readonly AcDream.Core.Vfx.EmitterDescRegistry _emitterRegistry = new();
     private AcDream.Core.Vfx.ParticleSystem? _particleSystem;
     private AcDream.Core.Vfx.ParticleHookSink? _particleSink;
+    // Phase 6 — retail PhysicsScript runtime. Receives PlayScript (0xF754)
+    // from the server and schedules the dat-defined hooks (particle spawns,
+    // sounds, light toggles) at their StartTime offsets.
+    private AcDream.Core.Vfx.PhysicsScriptRunner? _scriptRunner;
     private AcDream.App.Rendering.ParticleRenderer? _particleRenderer;
 
     // Remote-entity motion inference: tracks when each remote entity last
@@ -827,6 +831,12 @@ public sealed class GameWindow : IDisposable
         _particleSink = new AcDream.Core.Vfx.ParticleHookSink(_particleSystem);
         _hookRouter.Register(_particleSink);
 
+        // Phase 6c — PhysicsScript runner. Uses the DatCollection to
+        // resolve PlayScript ids, and the same ParticleHookSink the
+        // animation system uses, so CreateParticleHook fired from a
+        // script spawns through the normal particle pipeline.
+        _scriptRunner = new AcDream.Core.Vfx.PhysicsScriptRunner(_dats, _particleSink);
+
         // Phase G.2 lighting hooks: SetLightHook flips IsLit on
         // owner-tagged lights so ignite-torch animations light up,
         // extinguish-torch animations go dark.
@@ -1064,6 +1074,16 @@ public sealed class GameWindow : IDisposable
             _liveSession.PositionUpdated += OnLivePositionUpdated;
             _liveSession.TeleportStarted += OnTeleportStarted;
 
+            // Phase 6c — PlayScript (0xF754) arrives from the server as
+            // a (guid, scriptId) pair. Resolve the guid's current world
+            // position and feed the PhysicsScript runner; it schedules
+            // the script's hooks (particle spawns, sound cues, light
+            // toggles) at their StartTime offsets. This is the channel
+            // retail uses for spell casts, combat flinches, emote
+            // gestures, AND — per Agent #5 research — lightning
+            // flashes during stormy weather.
+            _liveSession.PlayScriptReceived += OnPlayScriptReceived;
+
             // Phase G.1: keep the client's day/night clock in sync with
             // server time. Fires once from ConnectRequest (initial seed)
             // and repeatedly on TimeSync-flagged packets.
@@ -2222,6 +2242,38 @@ public sealed class GameWindow : IDisposable
         Console.WriteLine($"live: teleport started (seq={sequence})");
     }
 
+    /// <summary>
+    /// Phase 6c — server-sent PlayScript (0xF754) handler. Routes the
+    /// <c>(guid, scriptId)</c> pair into <see cref="_scriptRunner"/>
+    /// with the CAMERA's current world position as the anchor. For
+    /// scene-wide storm effects (lightning) the camera is the right
+    /// reference frame since the flash is meant to be "around the
+    /// player." For per-entity effects the runner's dedupe by
+    /// <c>(scriptId, entityId)</c> keeps multiple simultaneous plays
+    /// working on different guids.
+    ///
+    /// <para>
+    /// Improvements for follow-up: look up the guid's actual last-
+    /// known world position from <c>_worldState</c> so per-entity
+    /// spell casts and emote gestures anchor correctly. For Phase 6
+    /// scope (lightning, which is Dereth-wide) the camera anchor is
+    /// sufficient.
+    /// </para>
+    /// </summary>
+    private void OnPlayScriptReceived(uint guid, uint scriptId)
+    {
+        if (_scriptRunner is null) return;
+
+        var camWorldPos = System.Numerics.Vector3.Zero;
+        if (_cameraController is not null)
+        {
+            System.Numerics.Matrix4x4.Invert(_cameraController.Active.View, out var iv);
+            camWorldPos = new System.Numerics.Vector3(iv.M41, iv.M42, iv.M43);
+        }
+
+        _scriptRunner.Play(scriptId, guid, camWorldPos);
+    }
+
     /// <summary>
     /// Phase A.1: streaming load delegate, runs on the worker thread.
     /// Reads the landblock from the dats, hydrates its stab entities (same
@@ -3602,6 +3654,11 @@ public sealed class GameWindow : IDisposable
 
         // Phase E.3: advance live particle emitters AFTER animation tick
         // so emitters spawned by hooks fired this frame get integrated.
+        // Tick the PhysicsScript runner BEFORE the particle system so any
+        // CreateParticleHook fired this frame has its emitter alive when
+        // the particle system advances.
+        _scriptRunner?.Tick((float)deltaSeconds);
+
         _particleSystem?.Tick((float)deltaSeconds);
 
         int visibleLandblocks = 0;

src/AcDream.Core.Net/WorldSession.cs

@@ -109,6 +109,29 @@ public sealed class WorldSession : IDisposable
     /// </summary>
     public event Action<HearSpeech.Parsed>? SpeechHeard;
 
+    /// <summary>
+    /// Phase 6 — server-broadcast PhysicsScript trigger. Fires when the
+    /// server sends a <c>PlayScriptId</c> (opcode 0xF754) packet —
+    /// wire format <c>[u32 opcode][u32 guid][u32 scriptId]</c>.
+    ///
+    /// <para>
+    /// This is retail's ONLY general-purpose "make a visual thing
+    /// happen" channel: spell casts, emote gestures, combat flinches,
+    /// portal storms, and lightning flashes during stormy weather all
+    /// flow through this opcode. Subscribers (typically
+    /// <c>GameWindow</c>) resolve the guid to the appropriate entity
+    /// position and dispatch to a <c>PhysicsScriptRunner</c>.
+    /// </para>
+    ///
+    /// <para>
+    /// Trail: <c>chunk_006A0000.c:12320-12336</c> opcode dispatch →
+    /// <c>FUN_00452060</c> → <c>FUN_00511800</c> → <c>FUN_005117a0</c>
+    /// (PhysicsObj::RunScript) → <c>FUN_0051bed0</c> (PhysicsScript
+    /// runtime). See <c>docs/research/2026-04-23-lightning-real.md</c>.
+    /// </para>
+    /// </summary>
+    public event Action<uint /*guid*/, uint /*scriptId*/>? PlayScriptReceived;
+
     /// <summary>
     /// Phase G.1: latest server Portal Year tick count. Seeded from the
     /// ConnectRequest handshake (r12 §1.3 — server sends absolute game
@@ -548,6 +571,22 @@ public sealed class WorldSession : IDisposable
                 var env = GameEventEnvelope.TryParse(body);
                 if (env is not null) GameEvents.Dispatch(env.Value);
             }
+            else if (op == 0xF754u)  // PlayScript — server triggers a PhysicsScript on a target guid
+            {
+                // Phase 6b: wire format `[u32 opcode][u32 guid][u32 scriptId]`
+                // per chunk_006A0000.c:12320 disassembly. Dispatch the
+                // event; GameWindow subscribes and feeds its
+                // PhysicsScriptRunner. This is the channel retail uses for
+                // lightning flashes, spell casts, emotes, combat FX, etc.
+                if (body.Length >= 12)
+                {
+                    uint targetGuid = System.Buffers.Binary.BinaryPrimitives
+                        .ReadUInt32LittleEndian(body.AsSpan(4, 4));
+                    uint scriptId   = System.Buffers.Binary.BinaryPrimitives
+                        .ReadUInt32LittleEndian(body.AsSpan(8, 4));
+                    PlayScriptReceived?.Invoke(targetGuid, scriptId);
+                }
+            }
             else if (op == 0xF751u)  // PlayerTeleport — server is moving us through a portal
             {
                 // Phase B.3: holtburger opcodes.rs confirms 0xF751 is the