Realign code with the 2026-07-31 rulings

The trash sorts by modified descending — the arrival rank mint retires
(Ranks.isOrderedForTrash one comparator, loader + merged order agree;
the legacy deleted: migration stamps modified from the tombstone
timestamp where parseable; delete undo steps validate existence-only;
agent guide v8). Trash selection goes kind-blind — ranges, marquee,
Select All, and the successor walk sweep both kinds; the guard moves to
the exits (mixed-payload drop refusal, copy/cut validation). The copy
stamping preflight widens back to comment depth (load-scoped posture —
the board always loads, the gesture refuses whole). Fixes a latent
no-op: trashed-lane drag restore never fired (DragSession.beginLanes
hard-coded the board container).

2403 tests in 413 suites green.

Claude-Session: https://claude.ai/code/session_01CqjXB7ASoWtbyoGod68k97

Kanban/UI/Board/BoardDrops.swift

@@ -535,6 +535,23 @@ struct BoardDropContext {
             cancelDrop()
             return false
         }
+        // **A mixed-kind drag never leaves the trash** (04-interactions.md ▸ The trash, ruled
+        // 2026-07-31 with kind-blind trash selection): "pickup is allowed — the selection is legal —
+        // but every out-of-trash drop target refuses the mixed payload, and the release surfaces a
+        // notice explaining the rule … the refused drag ends like any refusal, rows staying put".
+        //
+        // One guard for every out-of-trash target, because every one of them funnels through this
+        // commit — the lane masonries, the strip, the cross-board arrivals, and the window fallback
+        // alike. A *within*-trash release cannot reach it: the column declines `.trash`-container
+        // sessions outright (`TrashDrop.accepts`), so a trash-origin drag never holds a `.trash`
+        // proposal, and "within-trash drops stay inert" needs no clause here.
+        //
+        // The notice is the destination board's strip, which is where the user is looking.
+        guard !(session.container == .trash && session.mixesKinds) else {
+            store.banners.postMixedTrashDrag()
+            cancelDrop()
+            return false
+        }
         let ids = survivors.map { session.members[$0] }
         let folders = survivors.map { session.folders[$0] }
         let within = DragLocality.isSameBoard(sourceRoot, store.rootURL)