fix(ui): match retail spell bar controls

Place favorite-bar arrows by their authored sides, import rollover and pressed media through the shared scrollbar, and preserve manual offsets across passive refreshes. Carry the mixed-parent DAT anchor chain to a fixed 18-cell favorite viewport so overflow controls and the Cast button remain inside the retail-sized combat frame.

Co-authored-by: Codex <codex@openai.com>

docs/research/2026-07-23-retail-spellbar-overflow-pseudocode.md

@@ -13,12 +13,12 @@ Each of the eight `SpellCastSubMenu` groups contains:
 ```text
 favorite group
   scrollbar 0x100000B5, 685x36
-    decrement button 0x10000071, 23x36
+    increment reference 0x10000072, authored x=0, 23x36
+      Normal   0x06004CDE (left-facing arrow)
+      Rollover 0x06004CDF
+    decrement reference 0x10000071, authored x=63, 23x36
       Normal   0x06004CDC
       Rollover 0x06004CDD
-    increment button 0x10000072, 23x36
-      Normal   0x06004CDE
-      Rollover 0x06004CDF
   item list 0x100000B6, x=23, y=2, 639x32
 
 scrollbar property 0x77 = increment button 0x10000072
@@ -28,7 +28,12 @@ item-list property 0x71 = horizontal scrollbar 0x100000B5
 ```
 
 The spell-bar scrollbar has no authored track or thumb. Its 23-pixel buttons
-occupy the space immediately outside the 639-pixel item-list viewport.
+occupy the space immediately outside the 639-pixel item-list viewport. The
+property names do not determine their drawn side:
+`UIElement_Scrollbar::UpdateScrollingArea @ 0x00470AA0` places the 0x77
+increment reference at the leading/top-left edge and the 0x78 decrement
+reference at the trailing/bottom-right edge. For this horizontal fixture that
+means `0x06004CDE` on the left and `0x06004CDC` on the right.
 
 ## Initialization and ownership
 
@@ -85,8 +90,8 @@ UpdateScrollbarSize(horizontal):
 
 Scrollbar.UpdateLayout():
     scrollingArea = own rectangle
-    position decrement button at the start and subtract its authored width
-    position increment button at the end and subtract its authored width
+    position property-0x77 button at the start and subtract its authored width
+    position property-0x78 button at the end and subtract its authored width
     update thumb/track geometry, when those children exist
     Visible = NOT (Disabled AND HideDisabled)
 ```
@@ -95,6 +100,31 @@ For the favorite bar, disabled plus HideDisabled removes both arrows when every
 favorite/empty cell fits. With overflow, the arrows remain visible and the
 item list clips the horizontally translated cells.
 
+The combat LayoutDesc deliberately mixes design extents: its outer combat root
+is 610 pixels wide, while the magic page's children are authored against an
+800-pixel parent. Applying retail
+`UIElement::UpdateForParentSizeChange @ 0x00462640` through that complete
+raw-edge chain gives a 439-pixel favorite viewport at the 610-pixel root—the
+13-slot short bar seen before this slice.
+
+The retail presentation exposes 18 favorite cells: nine shortcut-numbered
+cells plus nine unnumbered cells. At 32 pixels per cell the target viewport is
+576 pixels. Because every horizontal raw-edge stage carries the parent delta
+one-for-one, solving the imported tree for that viewport yields:
+
+```text
+outer combat root = 747 px
+magic page         = 737 px (5 px inset on each side)
+favorite group     = 622 px (x=40, followed by Cast)
+scrollbar          = 622 px (23 + 576 + 23)
+favorite list      = 576 px (18 * 32)
+Cast               = x=662, width=75 inside the magic page
+```
+
+This is a fixed visible-capacity HUD, not a desktop-wide strip. Stretching it
+to the display width makes the favorite content fit, which legitimately
+disables and hides the `HideDisabled` overflow arrows.
+
 ## Scroll delta and selection exposure
 
 Retail:
@@ -127,15 +157,23 @@ SpellCastSubMenu.SetSelected(spellId):
 ```
 
 The favorite cells are 32 pixels wide, so a line arrow moves exactly 32
-pixels. Programmatic or keyboard selection exposes the selected cell even when
-it was outside the prior viewport.
+pixels. An actual programmatic, keyboard, or pointer selection exposes the
+selected cell even when it was outside the prior viewport. Passive endowment
+or object-table refresh does not re-run `SetSelected`; doing so would undo a
+manual scrollbar offset.
 
 ## Port constraints
 
 - Preserve the imported `0x71`/`0x77`/`0x78` relationships.
 - Preserve each authored button's dimension; do not assume the 16-pixel chat
   scrollbar button size.
+- Preserve each authored button's Normal, Normal_rollover, and Normal_pressed
+  media through the shared scrollbar presentation path.
 - Do not fabricate a track/thumb for this arrow-only control.
 - Derive disabled state from the shared model's content and viewport extents.
 - Hide disabled controls from both drawing and hit-testing.
 - Keep every favorite tab's scroll offset independent.
+- Carry the DAT raw-edge policies through the full imported combat tree and
+  solve the root width for an 18-cell (576-pixel) favorite viewport.
+- Keep the resulting 747-pixel HUD width fixed across desktop resizes; do not
+  turn the favorite bar into a desktop-wide strip.