Stream B.1 of the 2026-06-18 handoff — the shared widget-level drag-drop
infra that both shortcut-drag (B) and the inventory window (C) sit on.
Four design decisions confirmed with the user this session:
1. Payload = typed ItemDragPayload record snapshotted at drag-begin
(ObjId/SourceKind/SourceSlot/SourceCell); SourceContainer derived at
drop from ClientObjectTable (single source of truth).
2. Cursor ghost painted by UiRoot via a generic UiElement.GetDragGhost()
hook — keeps UiRoot item-agnostic; floats above all windows.
3. Cell (UiItemSlot) is the drop-target hit unit + accept/reject overlay
owner, delegating the decision + dispatch UP to its parent UiItemList's
registered IItemListDragHandler (faithful to retail cell->ItemList_DragOver
->m_dragHandler; scales to the inventory N-cell grid).
4. PR ships infra + a visible toolbar STUB handler (logs, no wire) so the
ghost/overlay/dispatch are confirmable this session; AddShortcut/Remove
wire is Stream B.2.
Retail-grounded: InqDropIconInfo flags (&0xE==0 fresh / &4 reorder, reject
state 0x10000040) confirmed live at gmToolbarUI 0x004bd162; the cell
begin-drag/CatchDroppedItem/RegisterItemListDragHandler chain at decomp
229344/229744/230461. Planned register rows: AP-47 (ghost reuses full icon
at reduced alpha vs retail m_pDragIcon) + TS-33 (toolbar drop stub pending
B.2). No new wire format in the spine itself.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
