## Summary
The scene widget's serializeValue uploaded a fresh temp image on every
queue, so the `image / mask / normal` filenames in the prompt JSON were
new each run. The backend cache key (which hashes those input strings)
never matched, forcing Load3D and every downstream node to re-execute
even when the user changed nothing.
Track a session-scoped dirty flag and last-output cache in module-level
WeakMaps keyed by LGraphNode. serializeValue returns the cached output
when nothing has changed; user actions that mutate the visible scene
(scene/model/camera/light config, animation, recording, gizmo, camera
orbit) mark dirty through useLoad3d watchers and event handlers. The
model_file / width / height widget callbacks invalidate via a new
optional onSceneInvalidated hook plumbed through Load3DConfiguration, so
the captured screenshot stays consistent with the inputs the backend
sees.
## Screenshots (if applicable)
Before
https://github.com/user-attachments/assets/5ee5f79f-dd38-401e-babe-4d6ea156e56d
After
https://github.com/user-attachments/assets/5e00beb4-937c-4c66-abb2-e455f5301de6
