The empty provider was never load-bearing — the dragless layer frees the rubber band

Measured on real events 2026-08-07, correcting the 2026-08-06 hosted
finding: a bare count-1 tap on LaneView's empty-space layer fires in
~1-3 ms with no drag source at all — the hold that made the empty
.onDrag look necessary was the sterile NSApp.postEvent stream
over-disambiguating. And the provider was actively harmful: even an
empty drag source claims the mouse-drag at threshold, starving the
marquee's simultaneous DragGesture after one sample — the band froze
and the mouseUp never arrived. The layer goes dragless; drags from
empty space belong wholly to MarqueeControl. PointerClick's and the
layer's comments retell the corrected story. Alongside: openCard is
typed @MainActor throughout, which makes the closure Sendable and
lets CardFaceRole carry it under CardFaceView's nonisolated ==.

Claude-Session: https://claude.ai/code/session_014PtZdPwqZuqEDLc6wZMtEy

Kanban/App/BoardWindowHost.swift

@@ -260,7 +260,7 @@ struct BoardWindowHost: View {
     /// Opens a card's window. `openWindow(value:)` with a ref that already has a window focuses it,
     /// so "at most one card window per card (reopen focuses)" needs no bookkeeping here
     /// (02-architecture.md § Windows).
-    private var openCard: (ItemID) -> Void {
+    private var openCard: @MainActor (ItemID) -> Void {
         { cardID in
             openWindow(id: WindowID.card, value: CardWindowRef(board: ref, cardID: cardID))
         }