feat(ui): the spell-bar drop ring — retail's authored drag-accept state, and the ring exposed a real drop off-by-one

The green ring is retail's own art: every UIItem cell carries an
authored DragAccept child (catalog 0x21000037, child 0x1000045A), and
the spell bar's drag-over handler (SpellCastSubMenu::OnItemListDragOver
@0x004C5990) flips it to the Accept state (0x10000040 -> surface
0x060011F9) for any spell payload. Ported through a per-slot
SetDragAcceptVisual seam + a catalog DragOverAcceptance hook; other
lists are untouched (null acceptance = neutral). A polarity error in
our older docs (Accept/Reject state ids swapped) was corrected against
three independent sources; the shipped art was always right, only the
labels lied.

The ring shares ONE landing computation with the drop
(FavoriteDropIndex) — and that requirement exposed a genuine #354
off-by-one: the empty-tail path double-applied the -1 adjustment
(retail gates it on the lift's removal @0x004C7157), landing a
reordered spell second-to-last instead of last. Fixed;
discriminator-verified both ways. AP-172 narrowed + its false
empty-tail claim corrected.

Clean-room complete solution: 11,545 passed / 4 skipped / 0 failed.

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

docs/research/2026-06-16-ui-item-slot-icon-dragdrop-spine-deep-dive.md

@@ -141,6 +141,19 @@ internal element states `SetDragAcceptState` writes — both are real; the Layou
 states and the `0x1000003x/4x` UIStateIds are the same overlay seen from the dat side vs.
 the C++ side. CONFIRMED.
 
+> **Correction 2026-08-08 (spell-bar drop-ring research):** the parenthetical
+> above has the accept/reject ids SWAPPED. The true mapping is
+> `ItemSlot_DragOver_Accept = 0x10000040 → 0x060011F9` and
+> `ItemSlot_DragOver_Reject = 0x10000041 → 0x060011F8`, confirmed by
+> DatReaderWriter's retail-derived `UIStateId` enum, by the legal/illegal
+> branches of `gmPaperDollUI::HandlePaperDollDragOver` @ 0x004A3AC9/0x004A3AEB
+> and `VendorSellUI::OnItemListDragOver` @ 0x004C2327/0x004C2336, and by the
+> machine layout dump (`2026-06-25-retail-ui-layout-dump.json`, states
+> 268435520/268435521 on elements 0x1000046D/0x1000046C). The table row's
+> name→art column above was always right; only this paragraph's numeric
+> pairing was inverted (and propagated into
+> `2026-07-13-retail-item-drag-visuals-pseudocode.md`, corrected the same day).
+
 ### 2.3 Key methods + the update pass (`UIItem_Update`, decomp 230226)
 
 `UIItem_Update` is the per-change refresh; the controller calls it whenever the bound

docs/research/2026-07-13-retail-item-drag-visuals-pseudocode.md

@@ -79,12 +79,28 @@ if target list is a container selector
     target.SetDragAcceptState(0x10000046)  # ItemSlot_DragOver_DropIn
                                            # 0x060011F7 green arrow
 else if target accepts an ordinary item-list placement:
-    target.SetDragAcceptState(0x10000041)  # ItemSlot_DragOver_Accept
+    target.SetDragAcceptState(0x10000040)  # ItemSlot_DragOver_Accept
                                            # 0x060011F9 green circle
 else:
-    target.SetDragAcceptState(0x10000040)  # 0x060011F8 reject
+    target.SetDragAcceptState(0x10000041)  # ItemSlot_DragOver_Reject
+                                           # 0x060011F8 reject
 ```
 
+> **Correction 2026-08-08 (spell-bar drop-ring research):** the block above
+> originally had the Accept/Reject numeric ids swapped (`0x10000041` labeled
+> Accept, `0x10000040` labeled reject). Three primary sources agree the true
+> mapping is `ItemSlot_DragOver_Accept = 0x10000040 → 0x060011F9` and
+> `ItemSlot_DragOver_Reject = 0x10000041 → 0x060011F8`: DatReaderWriter's
+> retail-derived `UIStateId` enum; the legal/illegal branches in
+> `gmPaperDollUI::HandlePaperDollDragOver` (`AutoWearIsLegal` → 0x10000040
+> @ 0x004A3AC9, else 0x10000041 @ 0x004A3AEB) and
+> `VendorSellUI::OnItemListDragOver` (`DragItemAcceptable` → 0x10000040
+> @ 0x004C2327, else 0x10000041 @ 0x004C2336); and the machine layout dump
+> (`2026-06-25-retail-ui-layout-dump.json`: state 268435520 = 0x10000040 →
+> image 0x060011F9, state 268435521 = 0x10000041 → 0x060011F8). The
+> art-per-semantic mapping in the shipped code was always correct; only the
+> numeric labels here were swapped.
+
 Therefore the backpack contents grid uses the green circle; the side-bag column
 and main-pack container cell use the green drop-in arrow. The selected/open
 indicators remain visible while `m_elem_Icon_Ghosted` is active, so the