fix(ui): Slice 5.4 review corrections — the dropdown renders from its authored popup, retail cost semantics, auto-select, icon overlays

All nine review findings closed at root (one sub-item consciously
deferred):

F1 the category dropdown now draws: sprites/fonts wired and the popup
geometry read from the vendor menu's own authored popup LayoutDesc
0x21000043 (root 0x1000034F — correcting the review's 0x1000014F
transcription) per UIElement_Menu::MakePopup (pc:120705); chat's menu
is untouched and its tests prove it. The new test drives selection
through the REAL open/hit path the review flagged as bypassed.
F2+F3 the selected-item cost display ports VendorItemsUI::UpdateItemsUI
verbatim: quantity via the 0xDC41CB0 split-size mask (whole-stack for
ammo, per-unit for groceries/components; mask lives at the toolbar
SEEDING site pc:198784), plural names with retail's
fall-back-to-singular (pc:409056 — correcting the review's "name+s"
guess), full cost sentences with comma grouping and the player's coin
total, and Buy/Add buttons that disable without a selection.
F4 category switches auto-select the first filtered item (pc:201180).
F5 icon underlay/overlay/effects + plural name forwarded from the
already-parsed wire fields through VendorShopItem to the icon
composer. F6 a DIFFERENT vendor opens on its own first category;
same-vendor refresh preserves per the clamp. F7 scroll resets on
rebuild and authored empty slots fill; the right-click examine route
is consciously DEFERRED (shop items are not in ClientObjectTable and
the appraisal panel hard-requires it — documented, not faked).
F8 VendorState.Apply's fanout gets the same per-listener isolation as
Close/Reset. F9 AP-110/AP-161 wording corrected ("quantity-correct
pricing") and AP-161 rewritten to exactly the remaining conscious
gaps.

Clean-room complete solution with the #348 cursor fix in the same
tree: 11,334 passed / 4 skipped / 0 failed.

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

src/AcDream.Core/Items/VendorState.cs

@@ -57,7 +57,25 @@ public readonly record struct VendorShopItem(
     // conditionally present (weenieFlags-gated) -- absent maps to null here,
     // matching retail's own zeroed-struct default of 0 for the same case
     // (see VendorPricing.PerUnitValue's <= 0 guard).
-    int? DescStackSize = null);
+    int? DescStackSize = null,
+    // Review finding F5 (Slice 5.4 review): PublicWeenieDescBody already
+    // carries these three (IconOverlayId/IconUnderlayId/UiEffects) — see
+    // AcDream.Core.Net.Messages.PublicWeenieDescBody. Mirrors
+    // ClientObjectTable's ClientObject.IconUnderlayId/IconOverlayId/Effects
+    // naming exactly, so VendorUiController can forward them to
+    // _resolveIcon the same way ExternalContainerController.CreateCell does
+    // (item.Type, item.IconId, item.IconUnderlayId, item.IconOverlayId,
+    // item.Effects). 0 = "not sent", same as ClientObject's convention.
+    uint IconUnderlayId = 0u,
+    uint IconOverlayId = 0u,
+    uint Effects = 0u,
+    // Review finding F2/F3 (Slice 5.4 review): retail's NAME_PLURAL display
+    // (ACCWeenieObject::GetObjectName, pc:409056-409132) reads
+    // PublicWeenieDesc::_plural_name -- wire AcDream.Core.Net.Messages.
+    // PublicWeenieDescBody.PluralName. Null/empty is a real, retail-modeled
+    // case (no plural authored): GetObjectName falls back to the singular
+    // Name unchanged, not an auto-pluralized "Name+s".
+    string? PluralName = null);
 
 public enum VendorStateTransitionKind
 {
@@ -135,10 +153,31 @@ public sealed class VendorState
         Profile = profile;
         Items = items;
 
-        Changed?.Invoke(new VendorTransition(
+        var transition = new VendorTransition(
             sameVendor ? VendorStateTransitionKind.Refreshed : VendorStateTransitionKind.Opened,
             previous,
-            vendorGuid));
+            vendorGuid);
+        // Review finding F8 (Slice 5.4 review): match Close()'s per-listener
+        // isolation + catch-and-log shape instead of a bare Invoke — Apply()
+        // is called from the SAME per-frame inbound-message-dispatch boundary
+        // (GameEventDispatcher.Dispatch's ApproachVendor handler) that
+        // Close()'s doc comment already establishes must survive a broken
+        // observer, and a bare Invoke lets the FIRST listener's exception
+        // starve every listener registered after it (e.g. a plugin panel
+        // wired after the retail VendorUiController).
+        Action<VendorTransition>? listeners = Changed;
+        if (listeners is not null)
+        {
+            foreach (Action<VendorTransition> listener in listeners.GetInvocationList())
+            {
+                try { listener(transition); }
+                catch (Exception error)
+                {
+                    Console.Error.WriteLine(
+                        $"[VendorState] Apply() observer threw: {error.Message}");
+                }
+            }
+        }
         return true;
     }