Land Finder file drops positionally, header release topmost

04's settled clauses were mostly shipped already — the create landing
resolved through DropSlotMath.cardSlot with one nominal shadow per
importable file — but a release on the lane header fell through to the
card zones, which clamp inward, so a scrolled lane could propose behind
the header stripe. FileDropZones now folds header, attach hit-test, and
card-slot resolution into one pure seam asked in that order, the header
answering topmost per the ruling; lane headers register their frames
for it. FinderDrop.shadowCount names the floor-at-one rule. New tests
pin the header boundary, a differential against cardSlot's own zones
(same zones, not similar), and a store-level differential proving a
file landing takes the very ranks a card move there takes.

Claude-Session: https://claude.ai/code/session_01SR4XGjmBE16ZUYWpfFHXwY

Kanban/UI/Board/LaneView.swift

@@ -132,6 +132,15 @@ struct LaneView: View {
                 )
             }
             .onDrag(startLaneDrag, preview: { dragReplica })
+            // **The header is the file drop's topmost position** (04-interactions.md ▸ Drag and drop,
+            // settled 2026-07-28: "a release on the lane header resolves to the topmost position —
+            // forgiving beats a dead stripe"). Its frame is registered rather than derived from the
+            // grid's because the grid is scroll-view *content*: scrolled down, its top edge climbs
+            // past the header and would stop being a boundary at all. The bar itself never moves.
+            .onGeometryChange(for: CGRect.self) { $0.frame(in: .global) } action: { frame in
+                drops.registry.update(header: frame, for: lane.id)
+            }
+            .onDisappear { drops.registry.removeHeader(lane.id) }
             .overlay(alignment: .trailing) { newCardButton }
             .contextMenu { laneMenu }
             // The lane's half of the Style… popover. Anchored on the header because that is the