Merge: collection ordering, and a range that says where it ends

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

# Conflicts:
#	docs/traceability.md
#	ui/dr-ui/src/collections_ui.rs
#	ui/dr-ui/src/library.rs
#	ui/dr-ui/ui/app.slint
#	ui/dr-ui/ui/library.slint
#	ui/dr-ui/ui/widgets.slint

ui/dr-ui/src/library_ui.rs

@@ -2245,6 +2245,23 @@ fn load_window(window: &AppWindow, ctl: &Rc<LibraryController>) {
         refresh_timeline(window, catalog, ctl);
     }
 
+    // TRACES: FR-CAT-7
+    // Whether this scope has an order a drag can change, which is what lets the
+    // grid draw an insertion caret and accept a drop.
+    //
+    // Answered here because this is the one place that runs on every re-read —
+    // a scope change, a reorder, a collection gaining a child that turns it
+    // into a set — so the caret cannot outlive the scope that justified it.
+    //
+    // The trash is never reorderable. It is a view of what was deleted, ordered
+    // by when, and it is not a collection at all.
+    window.set_library_manual_order(
+        !trash
+            && scope.is_some_and(|c| {
+                dr_catalog::collections::orders_manually(catalog.connection(), c).unwrap_or(false)
+            }),
+    );
+
     let cells = if trash {
         library::read_trashed_cells(catalog, offset, window_size)
     } else {