Vue retains scroll observers after its scroll element becomes null #1352

Describe the bug

Removing a scroll container while its Vue component stays mounted sets the template ref to null, but virtualizer.value.scrollElement still points to the detached node. A scroll event on that node still invokes onChange.

Your minimal, reproducible example

https://github.com/clean99/oss-pr-media/tree/main/tanstack-virtual/vue-null-scroll-element

From that directory, run HUSKY=0 LEFTHOOK=0 npm ci --registry=https://registry.npmjs.org && npm run dev and open the local URL.

Steps to reproduce

1. Click Hide catalog. The state shows getterIsNull: true, attached: true, connected: false, and cleanups: 0.
2. Click Dispatch detached scroll. The listener still runs: callbackDelta: 1.
3. Click Show catalog. The old observer finally cleans up (cleanups: 1).

Expected behavior

Hiding the container should clear scrollElement and clean up its observer. A detached scroll should produce callbackDelta: 0.

How often does this bug happen?

Every time.

Platform

macOS 26.5.2, Chromium 147.0.0.0, Node.js 24.8.0.

tanstack-virtual version

@tanstack/vue-virtual 3.13.50, @tanstack/virtual-core 3.19.9, Vue 3.5.22.

TypeScript version

JavaScript reproduction.

Additional context

getScrollElement accepts null. The options object and getter stay stable. The reproduction wraps the built-in offset observer to count cleanup and retains the old node to test its listener; it does not measure heap growth.

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• I understand that if my bug cannot be reliably reproduced in a debuggable environment, it will probably not be fixed and this issue may even be closed.