Live undo/redo: add/delete component and link, move, property edits

Undo and redo now work against a connected device; each step is sent
there through Sox. Deleting a component first reads its whole subtree
back (config, unloaded children, links, place among siblings) so undo
can recreate it; recreated components take new device ids, which the
DOM elements pick up so later steps still reach them. Binary Buf
config (a user's cred) is read with read_prop, since the cache decodes
every Buf as a Str. Moves, tidy layout, and Properties / page editor /
user edits record only what the device accepted.

A step that does not fully reach the device warns and clears the
history. History is also cleared on every view change in live mode,
as opening a sheet rebuilds the DOM from the device.

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

main.py

@@ -531,27 +531,27 @@ def _clear_restoring_flag():
 
 
 def do_undo(event=None):
-    if app_state.live_mode:
-        app_state.set_status("Undo is not available in live mode", warn=True)
-        return "break"
     label = undo.undo()
     if label is None:
         return "break"
-    app_state.window.title(f"{app_state.base_window_title()} — undid {label}")
+    app_state.window.title(f"{_base_title()} — undid {label}")
     return "break"
 
 
 def do_redo(event=None):
-    if app_state.live_mode:
-        app_state.set_status("Redo is not available in live mode", warn=True)
-        return "break"
     label = undo.redo()
     if label is None:
         return "break"
-    app_state.window.title(f"{app_state.base_window_title()} — redid {label}")
+    app_state.window.title(f"{_base_title()} — redid {label}")
     return "break"
 
 
+def _base_title():
+    if app_state.live_mode:
+        return app_state.base_window_title_live()
+    return app_state.base_window_title()
+
+
 def do_save(event=None):
     if app_state.live_mode:
         do_download_to_sax()
@@ -1771,11 +1771,12 @@ def on_canvas_release(event):
                             "Move", f"{comp_element.get('name', 'The component')} was not "
                             "moved on the device")
                         return
-                if not app_state.live_mode:
-                    undo.push(undo.MetaMoveCommand(
-                        [(comp_element, meta_before, raw_x, raw_y)],
-                        label=f"move {comp_element.get('name', 'component')}"
-                    ))
+                command_class = (undo.LiveMetaMoveCommand if app_state.live_mode
+                                 else undo.MetaMoveCommand)
+                undo.push(command_class(
+                    [(comp_element, meta_before, raw_x, raw_y)],
+                    label=f"move {comp_element.get('name', 'component')}"
+                ))
                 app_state.mark_dirty()
 
     app_state.drag_data["tag"] = None
@@ -2029,6 +2030,12 @@ def record_visit(kind, element):
     """
     global history_index, _history_file_path
 
+    # On a device, undo only reaches back as far as the view that is open. Opening a
+    # sheet reads the DOM afresh from the device, so steps taken before it name elements
+    # that are no longer there; Back and Forward are view changes too.
+    if app_state.live_mode:
+        undo.reset()
+
     if _suppress_history:
         return
 
@@ -2655,6 +2662,8 @@ def _live_tree_expand(comp_id, tree_item_id):
             def _ui():
                 global _restoring_selection
                 app_state.xml_root_element = sax_root
+                # A fresh DOM: undo steps name elements of the one it replaces.
+                undo.reset()
                 sax_file.refresh_treeview_from_dom(sax_root)
                 # Re-open and re-select the node without triggering a wiresheet
                 # re-render — the sheet is already showing the right content and