Fix Grid Scroll Flickering & Enhance VDOM State Synchronization

Description

This ticket addresses a critical race condition in the Buffered Grid component that caused visual flickering and infinite scroll loops during rapid scrolling. It also introduces a significant architectural enhancement to the VDOM state synchronization mechanism to ensure data consistency across worker threads.

The Issue

The Grid component suffered from a conflict between two scroll handling mechanisms:

1. Implicit: The global DomEvent hotpath calling onScrollCapture (sync), updating vnode/vdom.
2. Explicit: ScrollManager attaching manual scroll listeners (async/throttled) triggering update().

During rapid scrolling, the VDOM Worker would receive updates with conflicting or out-of-sync scroll states. Furthermore, the roundtrip to the VDOM worker resulted in a "clean" VNode structure that lacked the latest Main Thread scroll state captured by onScrollCapture. This caused the worker to generate "reset" deltas (e.g., setting scrollTop to 0), forcing the browser to jump and restarting the loop.

Changes

1. Grid Scroll Logic Refactoring

• Single Source of Truth: Removed the manual scroll listeners from src/grid/ScrollManager.mjs.
• onScrollCapture Implementation: Implemented onScrollCapture in src/grid/Body.mjs and src/grid/Container.mjs.
  • Calls super.onScrollCapture(data) to synchronously sync vnode and vdom state.
  • Forwards the event to ScrollManager to trigger the virtual row rendering logic.

2. VDOM State Synchronization Enhancement

• Renaming: Renamed syncVdomIds to syncVdomState globally (src/util/VDom.mjs, src/mixin/VdomLifecycle.mjs, usages) to reflect its expanded scope.
• Bidirectional Scroll Sync: Enhanced src/util/VDom.mjs to synchronize scroll state:
  • Preservation (VDOM -> VNode): Ensures that the live scroll position captured on the Main Thread (stored in vdom) overrides potentially stale state returning from the VDOM Worker. This prevents the worker response from resetting the scroll position.
  • Rehydration (VNode -> VDOM): Ensures that new VDOM trees (e.g., from Functional Components) inherit the persistent scroll state from the existing VNode.
• Documentation: Updated JSDoc for syncVdomState to explicitly explain the ID generation necessity and the bidirectional scroll logic.

Impact

• Eliminates grid scroll flickering and loops.
• Ensures VDOM/VNode consistency even when mutating state while update roundtrips are in flight.
• Improves stability for all components using saveScrollPosition.