Let the native clipboard through where the canvas has nothing to copy

A bound chord used to be `preventDefault`ed before its handler ran, so the
canvas took every ⌘C and ⌘V whether or not the node clipboard would act —
which is what blocked copying selected text out of the chrome floating over
the canvas. A binding may now return `false` to decline the key; ⌘C does so
when there is a text selection or no node selected, ⌘V when nothing of ours
is stored.

frontend/src/components/Flow/FlowEditor.tsx

@@ -1061,8 +1061,21 @@ function FlowEditorInner({
     {
       "mod+z": () => step(true),
       "mod+shift+z": () => step(false),
-      "mod+c": () => void copyNodes(),
-      "mod+v": pasteNodes,
+      // Both decline the key unless the node clipboard has something to do
+      // with it, so the native copy and paste still work on the canvas. A
+      // text selection wins outright: that is what the user asked to copy.
+      "mod+c": () => {
+        const selection = document.getSelection()
+        if (selection && !selection.isCollapsed) return false
+        if (!canvasNodes.some((node) => node.selected) && !selectedId) {
+          return false
+        }
+        void copyNodes()
+      },
+      "mod+v": () => {
+        if (!safeStorage.get(CLIPBOARD_KEY)) return false
+        pasteNodes()
+      },
       // ⌘P, not ⌘K: the sidebar's global search owns that everywhere, and this
       // palette is the canvas's own, narrower thing.
       "mod+p": () => setPaletteOpen((open) => !open),

frontend/src/lib/shortcuts.ts

@@ -6,8 +6,12 @@ import { useEffect, useRef } from "react"
  * A chord reads as `mod+shift+z`, where `mod` is ⌘ on a Mac and Ctrl
  * everywhere else. Bindings are plain data, so a view declares the whole set
  * it answers to in one place.
+ *
+ * A binding that returns `false` declines the key: it did nothing, so the
+ * browser's own default runs. That is how ⌘C stays a native copy whenever the
+ * canvas has nothing of its own to copy.
  */
-export type Shortcuts = Record<string, (event: KeyboardEvent) => void>
+export type Shortcuts = Record<string, (event: KeyboardEvent) => unknown>
 
 /** Text fields and the code editor keep their own bindings and their own undo. */
 export function isTextEntry(target: EventTarget | null): boolean {
@@ -55,8 +59,8 @@ export function useShortcuts(bindings: Shortcuts, inTextEntry: string[] = []) {
       ) {
         return
       }
+      if (run(event) === false) return
       event.preventDefault()
-      run(event)
     }
     window.addEventListener("keydown", onKeyDown)
     return () => window.removeEventListener("keydown", onKeyDown)