Delete a timeline row with everything in it

Delete or Backspace, or the × on the selected row, takes the node out of its
symbol along with every node hanging off it. One edit, so undo brings it back.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/arthur/domain/nest.cljs

@@ -144,6 +144,11 @@
   [nodes id]
   (into #{} (filter #(some #{id} (symbol/lineage nodes %))) (keys nodes)))
 
+(defn delete-node
+  "Take node `id` out of symbol `sid`, with everything hanging off it."
+  [clip sid id]
+  (clip/update-symbol clip sid update :nodes #(apply dissoc % (subtree % id))))
+
 (defn- transplant
   "Move node `id` from symbol `host`, where frame `frame` is showing, into symbol
   `target`, keeping where it is on screen and when. `carry` is the matrix from

frontend/src/arthur/events/history.cljs

@@ -7,6 +7,7 @@
             [arthur.domain.leaf :as leaf]
             [arthur.events.edit :as edit]
             [arthur.events.playback :as pb]
+            [arthur.events.ui :as ui]
             [arthur.footage.store :as store]
             [re-frame.core :as rf]))
 
@@ -66,16 +67,19 @@
   (or (#{"INPUT" "TEXTAREA" "SELECT"} (.-tagName target)) (.-isContentEditable target)))
 
 (defn install-keys!
-  "⌘Z / Ctrl+Z undoes, with Shift redoes, and Ctrl+Y redoes. Not while typing
-  in a field, where the browser's own undo is the one wanted."
+  "⌘Z / Ctrl+Z undoes, with Shift redoes, and Ctrl+Y redoes; Delete or
+  Backspace deletes the selected node, which undo brings back. Not while typing
+  in a field, where the browser's own keys are the ones wanted."
   []
   (.addEventListener
    js/window "keydown"
    (fn [^js e]
-     (when (and (or (.-metaKey e) (.-ctrlKey e)) (not (typing? (.-target e))))
+     (when-not (typing? (.-target e))
        (let [k (.toLowerCase (.-key e))]
-         (when-let [ev (cond (and (= k "z") (.-shiftKey e)) ::redo
-                             (= k "z") ::undo
-                             (= k "y") ::redo)]
+         (when-let [ev (if (or (.-metaKey e) (.-ctrlKey e))
+                         (cond (and (= k "z") (.-shiftKey e)) ::redo
+                               (= k "z") ::undo
+                               (= k "y") ::redo)
+                         (when (#{"delete" "backspace"} k) ::ui/delete-selected))]
            (.preventDefault e)
            (rf/dispatch [ev])))))))

frontend/src/arthur/events/ui.cljs

@@ -195,6 +195,16 @@
        (:refused r) (refused db (:refused r))
        :else (edit/edit db (constantly (:clip r)))))))
 
+(rf/reg-event-db
+ ::delete-selected
+ (fn [db _]
+   (let [[kind sid id] (get-in db [:ui :selection])]
+     (if (= :node kind)
+       (-> db
+           (edit/edit #(nest/delete-node % sid id))
+           (assoc-in [:ui :selection] nil))
+       db))))
+
 (rf/reg-event-db
  ::restack
  ;; Onto the edge of a row in another symbol, it goes into that symbol first:

frontend/src/arthur/ui/timeline.cljs

@@ -259,7 +259,13 @@
                    (rf/dispatch [::ui/toggle-row path]))}
       (when expandable? (if expanded? "▾" "▸"))]
      [:span.name label]
-     (when node? [:span.kind (str "·" (name node-kind))])]))
+     (when node? [:span.kind (str "·" (name node-kind))])
+     (when (and node? (= select selection))
+       [:button.tl-delete {:title    "delete, with everything in it (⌫)"
+                           :on-click (fn [^js e]
+                                       (.stopPropagation e)
+                                       (rf/dispatch [::ui/delete-selected]))}
+        "×"])]))
 
 (defn- track-cell
   "`sliding` is the pointer's side of a bar being dragged, `{:path :x :width