fix(ui): complete retail inventory scroll polish

Preserve pixel scroll offsets across inventory rebuilds, crop partially visible rows with nested geometry/UV clips, and replace the obsolete 560px resize ceiling with available screen height. Keep retail's row-sized wheel step while allowing continuous scrollbar thumb positions.

Co-Authored-By: Codex <codex@openai.com>

docs/research/2026-07-11-retail-inventory-scroll-pseudocode.md

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+# Retail inventory listbox scrolling pseudocode
+
+## Named-retail anchors
+
+- `UIElement_ListBox::ScrollToY @ 0x0046D550`
+- `UIElement_ListBox::InqScrollDelta @ 0x0046DC10`
+- `UIElement_ListBox::ScrollToView @ 0x0046E9F0`
+- `UIElement_Scrollable::SetScrollableXY @ 0x004740C0`
+- `UIElement_ItemList::ItemList_SetParentContainer @ 0x004E49D0`
+- `UIElement_ItemList::RefreshList @ 0x004E4C00`
+
+## Scroll model
+
+```text
+ScrollToY(pixelY):
+    SetScrollableXY(currentX, pixelY, false)
+
+InqScrollDelta(vertical, negativeDirection, page):
+    if page:
+        delta = viewportHeight
+    else if rowCount != 0:
+        delta = min(scrollableHeight / rowCount, viewportHeight)
+    else:
+        delta = 0
+    return negativeDirection ? -delta : delta
+```
+
+The stored position is an integer pixel coordinate, not a row index. Scrollbar
+thumb movement can therefore stop with a row partially visible. Wheel/arrow line
+steps remain one row high because `InqScrollDelta` derives the line delta from
+`scrollableHeight / rowCount`.
+
+`ScrollToView(index)` sums preceding row heights and compares that pixel rectangle
+against `[scrollY, scrollY + viewportHeight]`; it adjusts only when the item lies
+outside the visible pixel interval.
+
+## Refresh behavior
+
+```text
+RefreshList():
+    ItemList_SetParentContainer(parentContainerID, refresh=true, notify=true)
+
+ItemList_SetParentContainer(...):
+    update capacity
+    flush item elements
+    add current contained objects in order
+    // no ScrollToHome / SetScrollableXY(0) in this path
+```
+
+The item-element rebuild does not explicitly home the list. A client-side retained
+rebuild must therefore preserve `m_iScrollableY` and clamp it only after the complete
+replacement content establishes its final extent.
+
+## acdream port shape
+
+- `UiItemList.DeferLayout` prevents transient one-cell extents from clamping the
+  retained pixel offset during `InventoryController.Populate`.
+- Intersecting edge cells remain visible at their true `rowY - ScrollY` coordinate.
+- `UiElement.ClipsChildren` pushes a nested screen-space clip; `UiRenderContext`
+  crops sprite geometry and matching UVs, so a partial row paints only inside the
+  contents viewport and cannot receive input outside it.
+- The inventory window's maximum height is the available screen height rather than
+  the former arbitrary 560 px cap. Exact keystone resize bounds remain AP-54.