diff --git a/src/AcDream.Runtime/Physics/RuntimePlacementProjectionSubscription.cs b/src/AcDream.Runtime/Physics/RuntimePlacementProjectionSubscription.cs
new file mode 100644
index 00000000..bc48214c
--- /dev/null
+++ b/src/AcDream.Runtime/Physics/RuntimePlacementProjectionSubscription.cs
@@ -0,0 +1,119 @@
+using AcDream.Runtime.Entities;
+
+namespace AcDream.Runtime.Physics;
+
+/// <summary>
+/// Presentation-only sink for canonical Runtime SetPosition receipts.
+/// Implementations must apply an exact receipt idempotently: acknowledgement
+/// can fail after a successful projection when a re-entrant Runtime mutation
+/// revises the FIFO head, and the same immutable receipt may then be retried.
+/// </summary>
+public interface IRuntimePlacementProjectionSink
+{
+    bool TryApply(in RuntimePlacementProjectionSnapshot projection);
+}
+
+/// <summary>
+/// Shared graphical/no-window subscription which projects only the oldest
+/// canonical receipt and acknowledges it only after the host sink succeeds.
+/// Runtime remains the sole position, collision, residence, and lifetime
+/// authority; this class owns only its observer subscription and one
+/// idempotency token for a projection that succeeded before acknowledgement.
+/// </summary>
+public sealed class RuntimePlacementProjectionSubscription
+    : IRuntimePlacementObserver,
+      IDisposable
+{
+    private readonly RuntimePlacementProjectionChannel _channel;
+    private readonly Func<RuntimeGenerationToken> _generation;
+    private readonly IRuntimePlacementProjectionSink _sink;
+    private IDisposable? _subscription;
+    private RuntimePlacementProjectionToken _appliedAwaitingAcknowledgement;
+    private bool _disposed;
+
+    public RuntimePlacementProjectionSubscription(
+        GameRuntime runtime,
+        IRuntimePlacementProjectionSink sink)
+        : this(
+            runtime?.Placements
+                ?? throw new ArgumentNullException(nameof(runtime)),
+            () => runtime.Generation,
+            sink)
+    {
+    }
+
+    internal RuntimePlacementProjectionSubscription(
+        RuntimePlacementProjectionChannel channel,
+        Func<RuntimeGenerationToken> generation,
+        IRuntimePlacementProjectionSink sink)
+    {
+        _channel = channel ?? throw new ArgumentNullException(nameof(channel));
+        _generation = generation
+            ?? throw new ArgumentNullException(nameof(generation));
+        _sink = sink ?? throw new ArgumentNullException(nameof(sink));
+        _subscription = _channel.Subscribe(this);
+        _ = RetryPending();
+    }
+
+    public bool HasAppliedReceiptAwaitingAcknowledgement =>
+        _appliedAwaitingAcknowledgement.IsValid;
+
+    /// <summary>
+    /// Republishes Runtime's complete still-pending FIFO. Later receipts are
+    /// ignored until the exact oldest receipt projects and acknowledges.
+    /// </summary>
+    public bool RetryPending()
+    {
+        ObjectDisposedException.ThrowIf(_disposed, this);
+        RuntimeGenerationToken generation = _generation();
+        if (_appliedAwaitingAcknowledgement.IsValid
+            && (!_channel.TryPeek(
+                    generation,
+                    out RuntimePlacementProjectionSnapshot head)
+                || head.Token != _appliedAwaitingAcknowledgement))
+        {
+            _appliedAwaitingAcknowledgement = default;
+        }
+        return _channel.RetryPending(generation);
+    }
+
+    public void OnPlacement(in RuntimePlacementDelta delta)
+    {
+        if (_disposed
+            || !_channel.TryPeek(
+                delta.Stamp.Generation,
+                out RuntimePlacementProjectionSnapshot head)
+            || head != delta.Placement)
+        {
+            return;
+        }
+
+        RuntimePlacementProjectionToken token = head.Token;
+        if (_appliedAwaitingAcknowledgement != token)
+        {
+            if (!_sink.TryApply(in head))
+                return;
+            // A sink can synchronously tear down its host while applying a
+            // receipt. Leave that receipt pending for the replacement host;
+            // disposal is never permission to acknowledge afterward.
+            if (_disposed)
+                return;
+            _appliedAwaitingAcknowledgement = token;
+        }
+
+        if (_channel.Acknowledge(delta.Stamp.Generation, token)
+            && _appliedAwaitingAcknowledgement == token)
+        {
+            _appliedAwaitingAcknowledgement = default;
+        }
+    }
+
+    public void Dispose()
+    {
+        if (_disposed)
+            return;
+        _disposed = true;
+        Interlocked.Exchange(ref _subscription, null)?.Dispose();
+        _appliedAwaitingAcknowledgement = default;
+    }
+}
diff --git a/tests/AcDream.Runtime.Tests/Physics/RuntimePlacementProjectionSubscriptionTests.cs b/tests/AcDream.Runtime.Tests/Physics/RuntimePlacementProjectionSubscriptionTests.cs
new file mode 100644
index 00000000..541a0ac3
--- /dev/null
+++ b/tests/AcDream.Runtime.Tests/Physics/RuntimePlacementProjectionSubscriptionTests.cs
@@ -0,0 +1,415 @@
+using System.Collections.Immutable;
+using System.Numerics;
+using AcDream.Core.Net;
+using AcDream.Core.Net.Messages;
+using AcDream.Core.Physics;
+using AcDream.Runtime.Entities;
+using AcDream.Runtime.Physics;
+
+namespace AcDream.Runtime.Tests.Physics;
+
+public sealed class RuntimePlacementProjectionSubscriptionTests
+{
+    private const uint Landblock = 0xA9B40000u;
+    private const uint Cell = Landblock | 0x0001u;
+
+    [Fact]
+    public void SuccessfulSinkAcknowledgesExactPlaceSynchronously()
+    {
+        using var fixture = new Fixture();
+        var sink = new RecordingSink();
+        using var subscription = fixture.Subscribe(sink);
+
+        RuntimeSetPositionOutcome outcome = fixture.Place(
+            fixture.First,
+            new Vector3(12f, 18f, 7f));
+
+        Assert.Equal(
+            RuntimeSetPositionStatus.CommittedHostAcknowledgementPending,
+            outcome.Status);
+        RuntimePlacementProjectionSnapshot only = Assert.Single(sink.Applied);
+        Assert.Equal(RuntimePlacementProjectionKind.Place, only.Kind);
+        Assert.Equal(outcome.Projection, only.Token);
+        Assert.Equal(0, fixture.Lifetime.Placements.PendingCount);
+        Assert.False(subscription.HasAppliedReceiptAwaitingAcknowledgement);
+    }
+
+    [Fact]
+    public void RejectedSinkRetainsHeadAndRetryAppliesItExactly()
+    {
+        using var fixture = new Fixture();
+        bool ready = false;
+        var sink = new RecordingSink(_ => ready);
+        using var subscription = fixture.Subscribe(sink);
+        RuntimeSetPositionOutcome outcome = fixture.Place(
+            fixture.First,
+            new Vector3(13f, 18f, 7f));
+
+        Assert.Equal(1, fixture.Lifetime.Placements.PendingCount);
+        Assert.Single(sink.Applied);
+        Assert.False(subscription.HasAppliedReceiptAwaitingAcknowledgement);
+
+        ready = true;
+        Assert.True(subscription.RetryPending());
+
+        Assert.Equal(2, sink.Applied.Count);
+        Assert.All(sink.Applied,
+            projection => Assert.Equal(outcome.Projection, projection.Token));
+        Assert.Equal(0, fixture.Lifetime.Placements.PendingCount);
+    }
+
+    [Fact]
+    public void ThrowingSinkLeavesReceiptRetryableAndRecordsDispatchFailure()
+    {
+        using var fixture = new Fixture();
+        bool fail = true;
+        var sink = new RecordingSink(_ =>
+        {
+            if (fail)
+                throw new InvalidOperationException("host unavailable");
+            return true;
+        });
+        using var subscription = fixture.Subscribe(sink);
+        _ = fixture.Place(fixture.First, new Vector3(14f, 18f, 7f));
+
+        Assert.Equal(1, fixture.Lifetime.Placements.PendingCount);
+        Assert.Equal(1, fixture.Lifetime.Events.DispatchFailureCount);
+        Assert.IsType<InvalidOperationException>(
+            fixture.Lifetime.Events.LastDispatchFailure);
+
+        fail = false;
+        Assert.True(subscription.RetryPending());
+
+        Assert.Equal(2, sink.Applied.Count);
+        Assert.Equal(0, fixture.Lifetime.Placements.PendingCount);
+    }
+
+    [Fact]
+    public void LaterReceiptCannotProjectBeforeRejectedFifoHead()
+    {
+        using var fixture = new Fixture(secondEntity: true);
+        bool ready = false;
+        RuntimeEntityKey firstKey = fixture.First.Key!.Value;
+        var sink = new RecordingSink(projection =>
+            ready || projection.Token.Entity != firstKey);
+        using var subscription = fixture.Subscribe(sink);
+
+        _ = fixture.Place(fixture.First, new Vector3(15f, 18f, 7f));
+        _ = fixture.Place(fixture.Second!, new Vector3(16f, 18f, 7f));
+
+        RuntimePlacementProjectionSnapshot initial = Assert.Single(sink.Applied);
+        Assert.Equal(firstKey, initial.Token.Entity);
+        Assert.Equal(2, fixture.Lifetime.Placements.PendingCount);
+
+        ready = true;
+        Assert.True(subscription.RetryPending());
+
+        Assert.Equal(
+            [firstKey, firstKey, fixture.Second!.Key!.Value],
+            sink.Applied.Select(item => item.Token.Entity).ToArray());
+        Assert.Equal(0, fixture.Lifetime.Placements.PendingCount);
+    }
+
+    [Fact]
+    public void ReentrantReplacementProjectsRevisedDiscardBeforeAcknowledging()
+    {
+        using var fixture = new Fixture();
+        RuntimeEntityPlacementToken replacement = default;
+        var sink = new RecordingSink(projection =>
+        {
+            if (projection.Kind is RuntimePlacementProjectionKind.Place)
+            {
+                replacement = fixture.Lifetime.Physics.SetPosition
+                    .BeginAcceptedPlacement(
+                        fixture.First,
+                        fixture.First.PositionAuthorityVersion,
+                        RuntimeSetPositionOperationKind.RemoteAuthoritative);
+            }
+            return true;
+        });
+        using var subscription = fixture.Subscribe(sink);
+
+        RuntimeSetPositionOutcome original = fixture.Place(
+            fixture.First,
+            new Vector3(17f, 18f, 7f));
+
+        Assert.True(replacement.IsValid);
+        Assert.Equal(2, sink.Applied.Count);
+        Assert.Equal(RuntimePlacementProjectionKind.Place,
+            sink.Applied[0].Kind);
+        Assert.Equal(RuntimePlacementProjectionKind.Discard,
+            sink.Applied[1].Kind);
+        Assert.Equal(original.Projection.Sequence,
+            sink.Applied[1].Token.Sequence);
+        Assert.True(sink.Applied[1].Token.Revision
+            > original.Projection.Revision);
+        Assert.Equal(0, fixture.Lifetime.Placements.PendingCount);
+        Assert.False(subscription.HasAppliedReceiptAwaitingAcknowledgement);
+
+        fixture.Lifetime.Physics.SetPosition.Forget(
+            fixture.First,
+            releasePreparedMover: true);
+    }
+
+    [Fact]
+    public void ConstructorDrainsReceiptsCreatedBeforeSubscriptionInFifoOrder()
+    {
+        using var fixture = new Fixture(secondEntity: true);
+        RuntimeSetPositionOutcome first = fixture.Place(
+            fixture.First,
+            new Vector3(18f, 18f, 7f));
+        RuntimeSetPositionOutcome second = fixture.Place(
+            fixture.Second!,
+            new Vector3(19f, 18f, 7f));
+        Assert.Equal(2, fixture.Lifetime.Placements.PendingCount);
+        var sink = new RecordingSink();
+
+        using var subscription = fixture.Subscribe(sink);
+
+        Assert.Equal(
+            [first.Projection, second.Projection],
+            sink.Applied.Select(item => item.Token).ToArray());
+        Assert.Equal(0, fixture.Lifetime.Placements.PendingCount);
+        Assert.False(subscription.HasAppliedReceiptAwaitingAcknowledgement);
+    }
+
+    [Fact]
+    public void SyntheticWithdrawalUsesTheSameExactSinkAndAckPath()
+    {
+        using var fixture = new Fixture();
+        var sink = new RecordingSink();
+        using var subscription = fixture.Subscribe(sink);
+
+        Assert.True(fixture.Lifetime.Physics.SetPosition.Cancel(
+            fixture.First,
+            publishWithdrawal: true));
+
+        RuntimePlacementProjectionSnapshot withdrawal = Assert.Single(
+            sink.Applied);
+        Assert.Equal(RuntimePlacementProjectionKind.Withdraw, withdrawal.Kind);
+        Assert.Equal(fixture.First.Key, withdrawal.Token.Entity);
+        Assert.Equal(0, fixture.Lifetime.Placements.PendingCount);
+        Assert.False(subscription.HasAppliedReceiptAwaitingAcknowledgement);
+    }
+
+    [Fact]
+    public void DisposeUnsubscribesWithoutConsumingPendingRuntimeReceipt()
+    {
+        using var fixture = new Fixture();
+        var sink = new RecordingSink(_ => false);
+        var subscription = fixture.Subscribe(sink);
+        _ = fixture.Place(fixture.First, new Vector3(18f, 18f, 7f));
+        Assert.Equal(1, fixture.Lifetime.Events.PlacementSubscriberCount);
+
+        subscription.Dispose();
+
+        Assert.Equal(0, fixture.Lifetime.Events.PlacementSubscriberCount);
+        Assert.Equal(1, fixture.Lifetime.Placements.PendingCount);
+        Assert.Throws<ObjectDisposedException>(() =>
+            subscription.RetryPending());
+
+        var replacementSink = new RecordingSink();
+        using var replacement = fixture.Subscribe(replacementSink);
+        Assert.Single(replacementSink.Applied);
+        Assert.Equal(0, fixture.Lifetime.Placements.PendingCount);
+    }
+
+    [Fact]
+    public void ReentrantSinkDisposalNeverAcknowledgesAfterHostTeardown()
+    {
+        using var fixture = new Fixture();
+        RuntimePlacementProjectionSubscription? subscription = null;
+        var sink = new RecordingSink(_ =>
+        {
+            subscription!.Dispose();
+            return true;
+        });
+        subscription = fixture.Subscribe(sink);
+
+        _ = fixture.Place(fixture.First, new Vector3(19f, 18f, 7f));
+
+        Assert.Single(sink.Applied);
+        Assert.Equal(0, fixture.Lifetime.Events.PlacementSubscriberCount);
+        Assert.Equal(1, fixture.Lifetime.Placements.PendingCount);
+        Assert.False(subscription.HasAppliedReceiptAwaitingAcknowledgement);
+
+        var replacementSink = new RecordingSink();
+        using var replacement = fixture.Subscribe(replacementSink);
+        Assert.Single(replacementSink.Applied);
+        Assert.Equal(0, fixture.Lifetime.Placements.PendingCount);
+    }
+
+    private sealed class Fixture : IDisposable
+    {
+        private readonly RuntimeGenerationToken _generation = new(7UL);
+
+        internal Fixture(bool secondEntity = false)
+        {
+            Lifetime = new RuntimeEntityObjectLifetime(FlatEngine());
+            Lifetime.BindEventContext(
+                () => _generation,
+                static () => 11UL);
+            First = CreateRecord(Lifetime, 0x70002001u, 1);
+            AttachBody(Lifetime, First, new Vector3(10f, 20f, 7f));
+            if (secondEntity)
+            {
+                Second = CreateRecord(Lifetime, 0x70002002u, 1);
+                AttachBody(Lifetime, Second, new Vector3(11f, 20f, 7f));
+            }
+        }
+
+        internal RuntimeEntityObjectLifetime Lifetime { get; }
+        internal RuntimeEntityRecord First { get; }
+        internal RuntimeEntityRecord? Second { get; }
+
+        internal RuntimePlacementProjectionSubscription Subscribe(
+            IRuntimePlacementProjectionSink sink) => new(
+                Lifetime.Placements,
+                () => _generation,
+                sink);
+
+        internal RuntimeSetPositionOutcome Place(
+            RuntimeEntityRecord record,
+            Vector3 position) => Lifetime.Physics.SetPosition.Apply(
+                record,
+                record.PositionAuthorityVersion,
+                Command(position));
+
+        public void Dispose() => Lifetime.Dispose();
+    }
+
+    private sealed class RecordingSink(
+        Func<RuntimePlacementProjectionSnapshot, bool>? apply = null)
+        : IRuntimePlacementProjectionSink
+    {
+        internal List<RuntimePlacementProjectionSnapshot> Applied { get; } = [];
+
+        public bool TryApply(
+            in RuntimePlacementProjectionSnapshot projection)
+        {
+            Applied.Add(projection);
+            return apply?.Invoke(projection) ?? true;
+        }
+    }
+
+    private static RuntimeSetPositionCommand Command(Vector3 position) => new(
+        new PhysicsSetPositionRequest(
+            position,
+            Quaternion.Identity,
+            Cell,
+            position,
+            ImmutableArray<FlatCollisionSphere>.Empty,
+            Scale: 1f,
+            StepUpHeight: 0.4f,
+            StepDownHeight: 0.4f,
+            Flags: PhysicsSetPositionFlags.Placement
+                | PhysicsSetPositionFlags.Slide),
+        RuntimeSetPositionOperationKind.RemoteAuthoritative,
+        GameTime: 10d,
+        ExpectedVelocityAuthorityVersion: 0UL);
+
+    private static RuntimeEntityRecord CreateRecord(
+        RuntimeEntityObjectLifetime lifetime,
+        uint guid,
+        ushort incarnation)
+    {
+        RuntimeEntityRecord record = lifetime.RegisterEntity(
+            Spawn(guid, incarnation)).Canonical!;
+        lifetime.Entities.SetFinalPhysicsState(
+            record,
+            PhysicsStateFlags.Gravity);
+        return record;
+    }
+
+    private static void AttachBody(
+        RuntimeEntityObjectLifetime lifetime,
+        RuntimeEntityRecord record,
+        Vector3 position)
+    {
+        lifetime.Entities.SetFullCell(record, Cell, Landblock | 0xFFFFu);
+        var body = new PhysicsBody
+        {
+            Position = position,
+            Orientation = Quaternion.Identity,
+            LastUpdateTime = 1d,
+            State = PhysicsStateFlags.Gravity,
+            TransientState = TransientStateFlags.Active,
+        };
+        body.SnapToCell(Cell, position, position);
+        lifetime.Entities.SetPhysicsBody(record, body);
+        record.ObjectClock.Activate();
+        lifetime.Physics.AcknowledgeSpatialProjection(record, spatial: true);
+    }
+
+    private static PhysicsEngine FlatEngine()
+    {
+        var engine = new PhysicsEngine
+        {
+            DataCache = new PhysicsDataCache(),
+        };
+        engine.AddLandblock(
+            Landblock,
+            new TerrainSurface(new byte[81], new float[256]),
+            Array.Empty<CellSurface>(),
+            Array.Empty<PortalPlane>(),
+            worldOffsetX: 0f,
+            worldOffsetY: 0f);
+        return engine;
+    }
+
+    private static WorldSession.EntitySpawn Spawn(uint guid, ushort instance)
+    {
+        var position = new CreateObject.ServerPosition(
+            Cell, 10f, 20f, 7f, 1f, 0f, 0f, 0f);
+        var timestamps = new PhysicsTimestamps(
+            Position: 1,
+            Movement: 1,
+            State: 1,
+            Vector: 1,
+            Teleport: 0,
+            ServerControlledMove: 1,
+            ForcePosition: 0,
+            ObjDesc: 1,
+            Instance: instance);
+        var physics = new PhysicsSpawnData(
+            RawState: (uint)PhysicsStateFlags.Gravity,
+            Position: position,
+            Movement: null,
+            AnimationFrame: null,
+            SetupTableId: 0x02000001u,
+            MotionTableId: 0x09000001u,
+            SoundTableId: null,
+            PhysicsScriptTableId: null,
+            Parent: null,
+            Children: null,
+            Scale: null,
+            Friction: null,
+            Elasticity: null,
+            Translucency: null,
+            Velocity: null,
+            Acceleration: null,
+            AngularVelocity: null,
+            DefaultScriptType: null,
+            DefaultScriptIntensity: null,
+            Timestamps: timestamps);
+        return new WorldSession.EntitySpawn(
+            guid,
+            position,
+            0x02000001u,
+            Array.Empty<CreateObject.AnimPartChange>(),
+            Array.Empty<CreateObject.TextureChange>(),
+            Array.Empty<CreateObject.SubPaletteSwap>(),
+            null,
+            null,
+            "placement-projection-fixture",
+            null,
+            null,
+            0x09000001u,
+            PhysicsState: (uint)PhysicsStateFlags.Gravity,
+            InstanceSequence: instance,
+            MovementSequence: 1,
+            ServerControlSequence: 1,
+            PositionSequence: 1,
+            Physics: physics);
+    }
+}