Materialize the trash — store, undo, and the container universe

Phase 2 swaps every consumer: Liveness and its ancestor walk are gone,
replaced by ItemContainer — a UUID set plus the container side it
lives on, presence the whole test, one selection boundary instead of
the old liveness law. Deletion stages by place: board cards move to
the trash at a store-minted head rank, trash-side delete is permanent
behind its confirmation, Delete Immediately skips the trash from
anywhere, lane delete captures the subtree and removes the folder.
Restore has no method at all — moveCards resolves members in either
container, so drag-out and cut-paste are the ordinary moves 13 calls
them, registering ordinary Move steps. The delete inverse moves the
card back to its captured lane and rank; redo replays the captured
trash rank, a value the gesture actually wrote; lane undo recreates
the subtree byte-faithfully in session. Purges register nothing —
where 13's trash section contradicts its own Rules on that, Rules
wins, filed for ruling. Staleness collapsed to present-or-absent: a
container is a path, so a foreign restore fails the delete step's
expectation structurally. Legacy tombstones migrate on the loose-file
tail hook, cards oldest-first so minting above top reproduces the
retired newest-first column, lanes returning live, one folded loss
row naming both directions. Put Back, restoreByDrag,
receiveRestoredCards, TrashEntry, and the kind machinery are deleted;
the trash column renders the container correctly with its full face
rework left to phase 3.

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

KanbanTests/TaskCheckboxWriteTests.swift

@@ -328,19 +328,19 @@ struct StoreToggleTaskMarkerTests {
         #expect(try fixture.indexData(cardPath) == before)
     }
 
-    @Test("A tombstoned card's checkbox does not write")
-    func aTombstonedCardWritesNothing() throws {
+    @Test("A trashed card's checkbox does not write")
+    func aTrashedCardWritesNothing() throws {
         let fixture = try makeBoard()
         defer { fixture.tearDown() }
-        try BoardWriter.deleteItem(at: fixture.url(cardPath))
+        try fixture.move(cardPath, toTrash: Ident.card1)
         let store = try BoardStore(rootURL: fixture.root)
-        let before = try body(of: fixture, cardPath)
+        let before = try body(of: fixture, ".trash/\(Ident.card1)")
         let offsets = markerOffsets(in: checklistBody)
 
-        // Effective liveness, ancestor-walked (`BoardStore.liveItem`): a card in the trash renders
-        // nowhere, so nothing may write through a preview of it.
+        // `BoardStore.boardItem` is the board container and only it: a trashed card does not open,
+        // so nothing may write through a preview of one (03 ▸ Trash's no-editing rule).
         store.toggleTaskMarker(inCard: ItemID(rawValue: Ident.card1), bodyOffset: offsets[0], checked: false)
 
-        #expect(try body(of: fixture, cardPath) == before)
+        #expect(try body(of: fixture, ".trash/\(Ident.card1)") == before)
     }
 }