feat(edit): clipboard copy/paste of nodes

Add an internal clipboard on the controller with undoable macro paste, and
Copy/Paste menu actions and shortcuts in the main window. Covered by a test.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

pipeline_editor/controller.py

@@ -169,6 +169,7 @@ class EditorController:
         self.document = document
         self.library = library
         self.undo_stack = QUndoStack()
+        self._clipboard: list[dict] = []
 
     def add_node(self, template_key: str, x: float, y: float) -> Optional[NodeModel]:
         tmpl = self.library.get(template_key)
@@ -211,6 +212,31 @@ class EditorController:
         self.undo_stack.endMacro()
         return clones
 
+    def copy(self, node_ids) -> int:
+        """Snapshot the given nodes into the internal clipboard."""
+        self._clipboard = [self.document.node(nid).to_dict()
+                           for nid in node_ids if self.document.node(nid)]
+        return len(self._clipboard)
+
+    def paste(self, offset=(20, 20)) -> list:
+        """Recreate clipboard nodes with fresh ids as one undoable step."""
+        pasted = []
+        if not self._clipboard:
+            return pasted
+        self.undo_stack.beginMacro("Paste")
+        for data in self._clipboard:
+            node = NodeModel.from_dict(data)
+            fresh = node.clone(self.document.next_id("n"))
+            fresh.x += offset[0]
+            fresh.y += offset[1]
+            self.undo_stack.push(AddNodeCommand(self.document, fresh))
+            pasted.append(fresh)
+        self.undo_stack.endMacro()
+        return pasted
+
+    def can_paste(self) -> bool:
+        return bool(self._clipboard)
+
     def record_move(self, node_id: str, old, new) -> None:
         if old == new:
             return

pipeline_editor/main_window.py

@@ -97,6 +97,10 @@ class MainWindow(QMainWindow):
                                   triggered=self.delete_selection)
         self.act_dup = QAction("Du&plicate", self, shortcut="Ctrl+D",
                                triggered=self.duplicate_selection)
+        self.act_copy = QAction("&Copy", self, shortcut=QKeySequence.StandardKey.Copy,
+                                triggered=self.copy_selection)
+        self.act_paste = QAction("&Paste", self, shortcut=QKeySequence.StandardKey.Paste,
+                                 triggered=self.paste_clipboard)
 
         self.act_zoom_in = QAction("Zoom In", self, shortcut=QKeySequence.StandardKey.ZoomIn,
                                    triggered=lambda: self.view.scale(1.2, 1.2))
@@ -128,7 +132,7 @@ class MainWindow(QMainWindow):
         em = m.addMenu("&Edit")
         em.addActions([self.act_undo, self.act_redo])
         em.addSeparator()
-        em.addActions([self.act_delete, self.act_dup])
+        em.addActions([self.act_copy, self.act_paste, self.act_dup, self.act_delete])
 
         vm = m.addMenu("&View")
         vm.addActions([self.act_zoom_in, self.act_zoom_out, self.act_fit])
@@ -191,6 +195,15 @@ class MainWindow(QMainWindow):
         node_ids, _ = self._selected_ids()
         self.controller.duplicate(node_ids, offset=(self.config.grid_size, self.config.grid_size))
 
+    def copy_selection(self) -> None:
+        node_ids, _ = self._selected_ids()
+        n = self.controller.copy(node_ids)
+        self.statusBar().showMessage(f"Copied {n} node(s)")
+
+    def paste_clipboard(self) -> None:
+        g = self.config.grid_size
+        self.controller.paste(offset=(g, g))
+
     # -- view toggles -----------------------------------------------------
     def _toggle_grid(self, checked) -> None:
         self.config.show_grid = checked

tests/test_app.py

@@ -59,6 +59,18 @@ def test_duplicate_selection(win):
     assert len(list(win.document.nodes())) == n_before + 1
 
 
+def test_copy_paste(win):
+    win.load_sample()
+    node = next(win.document.nodes())
+    win.scene.node_items[node.node_id].setSelected(True)
+    n_before = len(list(win.document.nodes()))
+    win.copy_selection()
+    win.paste_clipboard()
+    assert len(list(win.document.nodes())) == n_before + 1
+    win.controller.undo()  # paste is one macro step
+    assert len(list(win.document.nodes())) == n_before
+
+
 def test_save_and_open_roundtrip(win, tmp_path):
     win.load_sample()
     path = tmp_path / "diagram.pipe"