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/UI/Board/CardFaceView.swift

@@ -30,11 +30,14 @@ import SwiftUI
 /// **Only the trash side carries the confirmation host** (settled): the board side's Delete is the
 /// ordinary staged move into `.trash/` and never stands an alert, so `board` needs nothing beyond the
 /// card opener.
-enum CardFaceRole {
+/// `Sendable` because `CardFaceView.==` is nonisolated and a nonisolated context may only read a
+/// main-actor `let` of Sendable type — which is why `openCard` is typed `@MainActor` (an isolated
+/// function type is Sendable; a bare one is not, and would sink the whole enum).
+enum CardFaceRole: Sendable {
 
     /// A card in a lane. Carries the board window's card opener — ⌘↩'s pointer twin
     /// (04-interactions.md ▸ Selection).
-    case board(openCard: (ItemID) -> Void)
+    case board(openCard: @MainActor (ItemID) -> Void)
 
     /// A card in `<root>/.trash/`. Carries the window's purge-alert host, because the trash's Delete
     /// is the permanent one and "confirms exactly where the loss is real" (03 § Trash).