Editing while playing: play runs on a runtime copy, new Game tab (Scene | Game | Graph)

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

README.md

@@ -16,20 +16,27 @@ Live: <https://nockal.com/game-maker/> · Widget playground: <https://nockal.com
 | **Collider** | A shape (box or circle) for collision detection, placed as a **child** of the object it belongs to (its *body*). Drawn as a green outline in edit mode only. |
 | **Override** | A per-object value that replaces the asset's value for one property. Only changed keys are stored; the inspector marks them bold and offers a reset (↺). |
 | **Default** | Every property has a schema default. Asset values that differ from it are marked bold in the inspector and can be reset (↺) the same way an override can. |
-| **Edit mode** | The viewport draws the project model; panels, grid, gizmos and drag-to-move are active. |
-| **Play mode** | A `World` is instantiated from the active scene (one entity per scene object, resolved properties as mutable state). Systems tick it; nothing writes back. **Stop discards the world.** |
+| **Edit mode** | The Scene tab draws the project model; panels, grid, gizmos and drag-to-move are active. |
+| **Play mode** | The editor switches to a **runtime copy** of the project (same ids). A `World` is instantiated from its active scene (one entity per scene object, resolved properties as mutable state) and shown in the **Game** tab. Systems tick it and mirror their changes into the copy; every panel stays open and edits the copy, which the world picks up immediately. **Stop discards world and copy** – the saved model is never touched. |
 
 **The camera defines what is rendered.** A camera asset has a view size (`width` × `height`,
-default 640×360) and a `zoom`; the frame it covers in world units is `size / zoom`. In edit
-mode that frame is drawn as an outline. In play mode only that frame is rendered – fitted into
-the viewport with black letterboxing – and objects outside it are culled. A scene without a
-camera renders nothing in play mode. Play has no built-in behaviour (no input, no movement):
+default 640×360) and a `zoom`; the frame it covers in world units is `size / zoom`. The Scene
+tab draws that frame as an outline. The Game tab renders only that frame – fitted into the
+view with black letterboxing – and objects outside it are culled. A scene without a camera
+renders nothing in the Game tab. Play has no built-in behaviour (no input, no movement):
 everything that happens is defined by behavior graphs.
 
+**Editing while playing.** Play opens the Game tab but leaves the editor fully usable: the
+Scene tab shows the live positions (symbols, gizmos and dragging included), the hierarchy and
+inspector show and edit the running objects, the graph can be changed, undo/redo work on the
+play session's own history. All of it happens in the runtime copy: values a behavior changes
+appear as overrides (bold, ↺ resets to the asset value), objects a graph destroys vanish from
+the lists, and Esc/Stop brings back exactly what was saved. Autosave pauses while playing.
+
 ## Behaviors (node graphs)
 
 A behavior asset holds a Blueprint-style graph edited in the **Graph** tab of the centre
-area (the **Scene** tab shows the viewport). Ports come in two kinds: **exec** (white
+area (the **Scene** tab shows the editable scene, the **Game** tab the running game). Ports come in two kinds: **exec** (white
 arrows, control flow) and **data** (coloured circles; `number`, `boolean`, `string`,
 `object`, `any`). Event nodes start a pulse; the interpreter follows exec edges and pulls
 data inputs lazily from connected outputs. Unconnected data inputs use the inline value
@@ -59,7 +66,7 @@ shown on the node and editable in the inspector.
   the empty canvas pans. Everything is undoable.
 - **Selection-bound**: the Graph tab shows the behavior the current selection refers to
   (asset, placed object or node); with nothing or a non-behavior selected it is empty.
-- **Live view**: Play always switches to the Scene tab; switch back to Graph while playing and
+- **Live view**: Play always switches to the Game tab; switch to Graph while playing and
   the exec edges and nodes that just ran light up – the same canvas draws editor and game, so
   this costs nothing extra.
 - **Runtime**: `BehaviorSystem` creates one `GraphInterpreter` per behavior entity; graphs only
@@ -132,7 +139,7 @@ src/core/           model, property schema, resolve, commands, store – no Pixi
 src/core/graph/     graph model, node registry + built-in nodes, interpreter (headless, unit-tested)
 src/runtime/        World, Entity, System interface, Input tracker, CollisionSystem, BehaviorSystem
 src/ui/             widget toolkit (generic, knows nothing about assets)
-src/viewport/       scene renderer: model in edit mode, world in play mode
+src/viewport/       scene renderer: Scene tab (model, editable) and Game tab (world through its camera)
 src/editor/         App composition, state, panels, inspector field factory
 src/editor/graph/   GraphEditor (canvas), NodeView, NodePalette
 api/                PHP backend            data/projects/   persisted projects