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/LiveStore/BoardStore.swift

@@ -1704,7 +1704,14 @@ public final class BoardStore {
     }
 
     /// Creates one card per file at `index` in `laneID`, each titled with its filename minus the
-    /// extension and carrying that file as its attachment — the drop-on-empty-space half.
+    /// extension and carrying that file as its attachment — the drop-into-a-lane half.
+    ///
+    /// **`index` is the drop position, not the lane's end** (04-interactions.md ▸ Drag and drop,
+    /// settled 2026-07-28): "created cards land at the drop position — resolved through the same
+    /// card-grid zones an ordinary card drag uses … drops are positional everywhere, and
+    /// append-at-bottom stays the creation *trio*'s rule, not the drop's". The gesture resolves it
+    /// through `FileDropZones.landing`; the rank arithmetic below is `moveCards`', so a run landing
+    /// between two siblings takes exactly the ranks a card drop there would have produced.
     ///
     /// **Ordinary store writes, with no drop-only path**: a fresh GUID and an inserted rank per card
     /// (`Ranks.insertionRanks`, compacting and placing again when midpoint precision is exhausted,