gum-tool-undo

name	gum-tool-undo
description	Gum undo/redo. Triggers: History tab, UndoManager, UndoPlugin, UndoSnapshot, stale references after undo.

Gum Undo/Redo System Reference

Overview

Gum has a snapshot-based undo/redo system scoped per-element. Undo history is displayed in the History tab in the Gum UI tool.

Key Characteristics

Per-Element Scoping

Undo history is stored separately for each open element (Screen, Component, or StandardElement). Switching between elements does not share or merge history — each element maintains its own independent undo stack.

No Selection Tracking

Undos do not record or restore the user's selection state. After undoing or redoing an operation, the selected object in the tree view or canvas may not match what was selected when the change was originally made.

No Persistence

Undo history is entirely in-memory and is cleared when the project is loaded or Gum is closed. There is no way to undo changes made in a previous session.

Element Deletion Is Not Undoable

When an element (Screen, Component, or StandardElement) is deleted, its entire undo history is discarded along with it. Deleting an element cannot be undone.

Behaviors Are Not Currently Supported

Undo/redo does not currently work for behavior-related changes. Changes to behaviors (adding, removing, or modifying) on an element may not be correctly undoable.

History Tab

The History tab in the Gum UI tool displays a human-readable list of all recorded undo actions for the currently selected element. Each entry shows a description of what changed, such as:

• Modify element variables: X=10
• Add instances: MySprite
• Remove instances: MySprite
• Add behaviors: MyBehavior
• Exposed variables: MyVar