From 4aebf444d910f8b0e18bfc642974750a49f0c117 Mon Sep 17 00:00:00 2001
From: Erik <erik.nihlen@gmail.com>
Date: Mon, 22 Jun 2026 19:51:20 +0200
Subject: [PATCH] feat(D.2b): wire ConfirmMove (0x0022 echo) + RollbackMove
 (0x00A0) for optimistic inventory moves

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
---
 src/AcDream.Core.Net/GameEventWiring.cs       | 17 ++++++++-------
 .../GameEventWiringTests.cs                   | 21 +++++++++++++++++++
 2 files changed, 31 insertions(+), 7 deletions(-)

diff --git a/src/AcDream.Core.Net/GameEventWiring.cs b/src/AcDream.Core.Net/GameEventWiring.cs
index fc425532..8f660948 100644
--- a/src/AcDream.Core.Net/GameEventWiring.cs
+++ b/src/AcDream.Core.Net/GameEventWiring.cs
@@ -246,8 +246,9 @@ public static class GameEventWiring
         dispatcher.Register(GameEventType.InventoryPutObjInContainer, e =>
         {
             var p = GameEvents.ParsePutObjInContainer(e.Payload.Span);
-            if (p is not null) items.MoveItem(p.Value.ItemGuid, p.Value.ContainerGuid,
-                newSlot: (int)p.Value.Placement);
+            if (p is null) return;
+            items.MoveItem(p.Value.ItemGuid, p.Value.ContainerGuid, newSlot: (int)p.Value.Placement);
+            items.ConfirmMove(p.Value.ItemGuid);   // B-Drag: the server confirmed our optimistic move
         });
 
         // ViewContents (0x0196) — the server's AUTHORITATIVE full contents list for a container you
@@ -273,14 +274,16 @@ public static class GameEventWiring
             if (guid is not null) items.MoveItem(guid.Value, newContainerId: 0u);
         });
 
-        // B-Wire: InventoryServerSaveFailed (0x00A0) — rollback of a speculative move.
-        // acdream does not do speculative moves yet (read-only inventory); parse + log
-        // so the wire is correct. B-Drag wires the rollback behavior. (Divergence note.)
+        // B-Drag: InventoryServerSaveFailed (0x00A0) — server rejected an optimistic move.
+        // Snap the item back to its pre-move slot. Log only when there was no pending move
+        // (a server-initiated failure on a non-optimistic path).
         dispatcher.Register(GameEventType.InventoryServerSaveFailed, e =>
         {
             var p = GameEvents.ParseInventoryServerSaveFailed(e.Payload.Span);
-            if (p is not null)
-                Console.WriteLine($"[B-Wire] InventoryServerSaveFailed guid=0x{p.Value.ItemGuid:X8} err=0x{p.Value.WeenieError:X}");
+            if (p is null) return;
+            // B-Drag: the server rejected an optimistic move — snap the item back to its pre-move slot.
+            if (!items.RollbackMove(p.Value.ItemGuid))
+                Console.WriteLine($"[B-Drag] InventoryServerSaveFailed guid=0x{p.Value.ItemGuid:X8} err=0x{p.Value.WeenieError:X} (no pending move)");
         });
 
         // B-Wire: CloseGroundContainer (0x0052) — server closed a ground-container
diff --git a/tests/AcDream.Core.Net.Tests/GameEventWiringTests.cs b/tests/AcDream.Core.Net.Tests/GameEventWiringTests.cs
index 24d868f3..92d7b471 100644
--- a/tests/AcDream.Core.Net.Tests/GameEventWiringTests.cs
+++ b/tests/AcDream.Core.Net.Tests/GameEventWiringTests.cs
@@ -585,6 +585,27 @@ public sealed class GameEventWiringTests
         d.Dispatch(env!.Value);
     }
 
+    [Fact]
+    public void WireAll_InventoryServerSaveFailed_RollsBackOptimisticMove()
+    {
+        var (d, items, _, _, _) = MakeAll();
+        // An item known to be in container 0xC0 at slot 2, then optimistically moved to 0xC1.
+        items.RecordMembership(0x50000B01u, containerId: 0x500000C0u);
+        items.MoveItem(0x50000B01u, 0x500000C0u, 2);
+        items.MoveItemOptimistic(0x50000B01u, 0x500000C1u, 0);
+        Assert.Equal(0x500000C1u, items.Get(0x50000B01u)!.ContainerId);   // moved (optimistic)
+
+        // Server bounces it: InventoryServerSaveFailed (itemGuid, weenieError).
+        byte[] payload = new byte[8];
+        BinaryPrimitives.WriteUInt32LittleEndian(payload.AsSpan(0), 0x50000B01u);
+        BinaryPrimitives.WriteUInt32LittleEndian(payload.AsSpan(4), 0x1Au);   // some WeenieError
+        var env = GameEventEnvelope.TryParse(WrapEnvelope(GameEventType.InventoryServerSaveFailed, payload));
+        d.Dispatch(env!.Value);
+
+        Assert.Equal(0x500000C0u, items.Get(0x50000B01u)!.ContainerId);   // snapped back
+        Assert.Equal(2, items.Get(0x50000B01u)!.ContainerSlot);
+    }
+
     [Fact]
     public void WireAll_InventoryPutObjectIn3D_UnparentsFromContainer()
     {