feat(runtime): Slice 5.3 — RuntimeInventoryState owns the vendor browse session

The sole VendorState joins the J4.2 inventory owners: populated by the
new 0x0062 ApproachVendor route (parse via VendorApproach, wire-to-
domain mapping at the routing seam, silent-drop on malformed like every
sibling), borrowed by both graphical and headless hosts, and torn down
through the EXISTING ExternalContainer reset stage — session reset,
portal-out, and logout all funnel through the one mechanism. Close is
client-local per retail (nothing on the wire): a range watcher rides
the existing per-advanced-frame publishMovement callback, using the
vendor's own authored UseRadius (ACE's 0.6 m fallback when absent).
The dormant ItemInteractionController ActiveVendorId seam is finally
wired as a live delegate — real id while open, 0 the moment the
session clears.

AP-160 filed in this same commit: the watcher measures plain 3D center
distance rather than retail's cylinder-gap, because Runtime has no
per-NPC collision radius/height source; bounded sub-meter, client-
local UI only.

Twelve Runtime tests: populate/field mapping, vendor replacement,
range clear + within-range retention, all three generation teardowns,
the ActiveVendorId seam, malformed-event drop. Clean-room complete
solution: 11,302 passed / 4 skipped / 0 failed.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/AcDream.Runtime/Gameplay/RuntimeInventoryState.cs

@@ -15,7 +15,9 @@ public readonly record struct RuntimeInventoryOwnershipSnapshot(
     int ShortcutCount,
     int ShortcutSubscriberCount,
     long ShortcutDispatchFailureCount,
-    long TransactionDispatchFailureCount)
+    long TransactionDispatchFailureCount,
+    // Slice 5.3: the sole open vendor shop id, 0 when no session is open.
+    uint VendorId)
 {
     public bool IsConverged =>
         IsDisposed
@@ -27,7 +29,8 @@ public readonly record struct RuntimeInventoryOwnershipSnapshot(
         && CurrentContainerId == 0u
         && ItemManaCount == 0
         && ShortcutCount == 0
-        && ShortcutSubscriberCount == 0;
+        && ShortcutSubscriberCount == 0
+        && VendorId == 0u;
 }
 
 /// <summary>
@@ -48,6 +51,13 @@ public sealed class RuntimeInventoryState : IDisposable
         ItemMana = new ItemManaState();
         Shortcuts = new ShortcutStore();
         Transactions = new InventoryTransactionState(_entityObjects.Objects);
+        // Slice 5.3: VendorState joins RuntimeInventoryState exactly the way
+        // ExternalContainerState does (research doc
+        // docs/research/2026-08-08-slice5-vendor-browse-research.md §C.2) —
+        // same "authoritative server-driven full-replace view... with a
+        // Changed event for presentation observers" shape, generation-gated
+        // and torn down alongside the rest of this owner's children.
+        Vendor = new VendorState();
         View = new InventoryStateView(this);
     }
 
@@ -56,6 +66,7 @@ public sealed class RuntimeInventoryState : IDisposable
     public ItemManaState ItemMana { get; }
     public ShortcutStore Shortcuts { get; }
     public InventoryTransactionState Transactions { get; }
+    public VendorState Vendor { get; }
     public IRuntimeInventoryStateView View { get; }
     public bool IsDisposed => _disposed;
 
@@ -71,11 +82,13 @@ public sealed class RuntimeInventoryState : IDisposable
         Shortcuts.Count,
         Shortcuts.SubscriberCount,
         Shortcuts.DispatchFailureCount,
-        Transactions.DispatchFailureCount);
+        Transactions.DispatchFailureCount,
+        Vendor.VendorId);
 
     public void ResetExternalContainer() => ExternalContainers.Reset();
     public void ResetTransactions() => Transactions.ResetSession();
     public void ResetItemMana() => ItemMana.Clear();
+    public void ResetVendor() => Vendor.Reset();
 
     public void ResetPlayerSnapshots()
     {
@@ -142,6 +155,7 @@ public sealed class RuntimeInventoryState : IDisposable
         try
         {
             Try(() => ExternalContainers.Reset(), ref failures);
+            Try(() => Vendor.Reset(), ref failures);
             Try(ItemMana.Clear, ref failures);
             Try(Shortcuts.Dispose, ref failures);
             Try(Transactions.Dispose, ref failures);

src/AcDream.Runtime/Gameplay/RuntimeVendorRangeQuery.cs

@@ -0,0 +1,110 @@
+using System.Numerics;
+using AcDream.Core.Items;
+using AcDream.Core.Net.Messages;
+using AcDream.Core.Physics;
+using AcDream.Runtime.Entities;
+
+namespace AcDream.Runtime.Gameplay;
+
+/// <summary>
+/// Client-local vendor-panel distance watcher (Slice 5.3, research doc
+/// <c>docs/research/2026-08-08-slice5-vendor-browse-research.md</c> §A.3/§B.1/
+/// §B.2). Retail's <c>gmVendorUI::OpenVendor</c> (pc:203650, 0x004C4BA0)
+/// registers a range handler via <c>CPlayerSystem::RegisterObjectRangeHandler</c>
+/// (pc:203677, 0x004C4C34) keyed to the vendor's OWN
+/// <c>PublicWeenieDesc._useRadius</c>; <c>gmVendorUI::OnObjectRangeExit</c>
+/// (pc:199486, 0x004C02F0) then calls <c>gmVendorUI::CloseVendor</c>
+/// (pc:202080, 0x004C3020) — a pure client-side teardown, no wire message.
+/// ACE's server-side belt-and-suspenders equivalent, <c>Vendor.CheckClose</c>
+/// (<c>references/ACE/Source/ACE.Server/WorldObjects/Vendor.cs:322-367</c>),
+/// polls every 1.5 s and closes when <c>GetCylinderDistance(lastPlayer) &gt;
+/// UseRadius</c>, falling back to <c>wo.UseRadius ?? 0.6f</c> when the vendor
+/// carries no explicit radius (<c>WorldObject_Use.cs:50,57</c>).
+/// </summary>
+public static class RuntimeVendorRangeQuery
+{
+    /// <summary>ACE <c>WorldObject_Use.cs:50</c>: <c>wo.UseRadius ?? 0.6f</c>.</summary>
+    private const float DefaultUseRadius = 0.6f;
+
+    /// <summary>
+    /// Close the open vendor session (if any) once the local player has
+    /// moved beyond the vendor's own UseRadius. No-op when no vendor is
+    /// open, or when either side's live position cannot be resolved this
+    /// tick (matches the existing App-layer convention at
+    /// <c>WorldSelectionQuery.IsWithinExternalContainerUseRange</c>: "the
+    /// server remains authoritative while render projection is absent" —
+    /// never force-close on missing data).
+    ///
+    /// <para>
+    /// <b>Distance metric divergence (register AP-160):</b> retail/ACE close
+    /// on CYLINDER-GAP distance — both objects' own collision radius and
+    /// height subtracted from the center distance
+    /// (<c>Position::cylinder_distance</c>/ACE's <c>GetCylinderDistance</c>).
+    /// Runtime does not resolve a live per-NPC collision radius/height
+    /// outside the App-layer's Setup-cylinder resolver
+    /// (<c>WorldSelectionQuery</c>, App-only — out of reach per the
+    /// Core-structure rules), so this uses plain 3D center-to-center
+    /// distance via <see cref="ObjectRangeMath.ObjectsInRange"/>'s
+    /// <c>useRadii: false</c> branch instead. Effect: the panel can close up
+    /// to (player radius + vendor radius) sooner than exact retail —
+    /// typically well under a meter for a two-legged NPC.
+    /// </para>
+    /// </summary>
+    public static void EnforceRange(GameRuntime runtime)
+    {
+        ArgumentNullException.ThrowIfNull(runtime);
+
+        VendorState vendor = runtime.InventoryOwner.Vendor;
+        uint vendorId = vendor.VendorId;
+        if (vendorId == 0u)
+            return;
+
+        uint playerGuid = runtime.PlayerIdentity.ServerGuid;
+        if (playerGuid == 0u
+            || !runtime.EntityObjects.Entities.TryGetActive(
+                playerGuid,
+                out RuntimeEntityRecord playerRecord)
+            || playerRecord.Snapshot.Position is not { } playerPosition)
+        {
+            return;
+        }
+
+        if (!runtime.EntityObjects.Entities.TryGetActive(
+                vendorId,
+                out RuntimeEntityRecord vendorRecord)
+            || vendorRecord.Snapshot.Position is not { } vendorPosition)
+        {
+            return;
+        }
+
+        float useRadius = vendorRecord.Snapshot.UseRadius ?? DefaultUseRadius;
+        bool inRange = ObjectRangeMath.ObjectsInRange(
+            AbsolutePosition(playerPosition),
+            0f,
+            0f,
+            AbsolutePosition(vendorPosition),
+            0f,
+            0f,
+            useRadius,
+            useRadii: false,
+            ignoreZDelta: false);
+
+        if (!inRange)
+            vendor.Close();
+    }
+
+    /// <summary>
+    /// Same reconstruction <see cref="RuntimeHostileTargetQuery"/> uses:
+    /// wire local XYZ plus the landblock-prefix world offset (each
+    /// landblock is 192 m).
+    /// </summary>
+    private static Vector3 AbsolutePosition(CreateObject.ServerPosition position)
+    {
+        int landblockX = (int)((position.LandblockId >> 24) & 0xFFu);
+        int landblockY = (int)((position.LandblockId >> 16) & 0xFFu);
+        return new Vector3(
+            position.PositionX + landblockX * 192f,
+            position.PositionY + landblockY * 192f,
+            position.PositionZ);
+    }
+}