fix(vendor): Slice 6 review corrections — ownership-checked retire, live slider display, drag-proof shop rows, hardened buy reservation

All nine findings from the buy-arc review, at root:

F1 the materializer's retire pass re-checks ownership (guid->vendorId
map; remove only while the live object's ContainerId still equals the
recording vendor) — buying a player-sold UNIQUE no longer deletes the
item you just purchased; the discriminating reparent-then-refresh test
pins it. F2 the cost/name display subscribes to the live split state
and shares ONE quantity computation with Buy (retail re-renders per
slider tick: RecvNotice_StackSliderChanged 0x004C4500) — the sentence
and the charge can no longer disagree. F3 shop rows never mint drag
payloads (UiItemSlot.AllowDragSource gates both IsDragSource AND
GetDragPayload — the second gate was caught by this pass's own test).
F4 sendBuy reports whether anything was sent; a null-session buy
cancels the reservation instead of leaking BusyCount forever.
F5 the retire loop snapshots, isolates per-guid observer failures, and
clears its tracking in finally and Dispose — teardown convergence can
no longer wedge. F6 auto-select is retail's unconditional
first-filtered-item shape (pc:201180-201184; the survival-check was
our invention and the comment claiming otherwise is corrected).
F7 non-stack buys clamp to quantity 1 locally (BuySingleItem
pc:201669). F8 the Add button is hard-disabled until staging exists.
F9 AP-161/162/163 rewritten to the post-fix reality.

Clean-room complete solution: 11,378 passed / 4 skipped / 0 failed.
The #350 render-ledger overflow observed this session is under
separate investigation and is NOT addressed here.

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

src/AcDream.App/Composition/InteractionRetainedUiComposition.cs

@@ -365,12 +365,17 @@ internal sealed class RetailInteractionRetainedUiCompositionFactory
             // Slice 6.3: ItemInteractionController.TryBuy owns the
             // reservation dance itself (see its doc comment); this is a
             // plain wire send, not a second requestUse-shaped delegate.
+            // F4 (Slice 6 review): report whether the send actually
+            // happened — a null CurrentSession or a not-in-world session
+            // must return false so TryBuy releases the reservation instead
+            // of marking it dispatched for a request nothing ever sent.
             sendBuy: (vendorGuid, itemGuid, amount, alternateCurrencyId) =>
-                session.CurrentSession?.SendBuy(
-                    vendorGuid,
-                    itemGuid,
-                    amount,
-                    alternateCurrencyId));
+            {
+                if (session.CurrentSession is not { } activeSession || !session.IsInWorld)
+                    return false;
+                activeSession.SendBuy(vendorGuid, itemGuid, amount, alternateCurrencyId);
+                return true;
+            });
     }
 
     public MagicRuntime CreateMagicRuntime(
@@ -671,8 +676,8 @@ internal sealed class RetailInteractionRetainedUiCompositionFactory
                     // guid" — Slice 6.1 guarantees a materialized shop
                     // item's ContainerId IS the vendor's guid, so this reads
                     // straight off the same ClientObjectTable/VendorState
-                    // pair VendorUiController.VendorSplitSize's display-only
-                    // copy also reads, through the SAME VendorSplitPolicy
+                    // pair VendorUiController.ResolveBuyQuantity (F2, Slice 6
+                    // review) also reads, through the SAME VendorSplitPolicy
                     // mask helper (no second mask copy).
                     guid =>
                         d.Inventory.Vendor.VendorId != 0u