fix(memory-graph): keep node selection when pagination changes the node count

[abhay-codes07]

What

Pin a node's popover in the memory graph, zoom out far enough for the load-more trigger to fetch the next page, and the popover vanishes mid-read.

The slideshow effect in memory-graph.tsx depends on nodes.length, and its inactive branch unconditionally cleared the selected node:

useEffect(() => {
    if (!isSlideshowActive || nodes.length === 0) {
        if (!isSlideshowActive) {
            setSelectedNode(null)   // runs on every node-count change
            ...

With the slideshow off (the default for every consumer), any change in node count re-ran the effect and wiped the user's selection — pagination appending documents being the common trigger. It also fired a stray coolDown() on the simulation each time.

Fix

Track the previous slideshow state in a ref and only clear the selection on a genuine active → inactive transition. Re-runs caused by nodes.length changing while the slideshow was never active are now no-ops.

Testing

• bun run test in packages/memory-graph — 188 pass
• bun run check-types — clean

Behaviour notes for review: the active → inactive transition still clears the selection and cools the simulation exactly as before; the only change is that re-runs where the slideshow was never active no longer touch the selection.

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[ishaanxgupta]

I don't think this issue exists in prod, I checked and could not reproduce this closing this for now, if you find this issue in prod, feel free to tag me

[abhay-codes07]

@ishaanxgupta thanks for checking. Taking you up on the "tag me" offer, because I think this reproduces on the default path rather than through the slideshow.

The trigger is not the slideshow being on, it is the effect re-running while the slideshow is off. On current main, memory-graph.tsx:

useEffect(() => {
    if (!isSlideshowActive || nodes.length === 0) {
        if (!isSlideshowActive) {
            setSelectedNode(null)      // clears selection on *every* re-run
            simulationRef.current?.coolDown()
        }
        return
    }
    // ...
}, [isSlideshowActive, nodes.length])   // re-runs whenever nodes.length changes

isSlideshowActive defaults to false for every consumer, so the effect sits in that top branch. Because nodes.length is a dependency, the effect re-runs any time the node count changes, and each re-run unconditionally calls setSelectedNode(null).

Repro without the slideshow:

1. Open the graph normally (slideshow off).
2. Click a node so its popover is pinned (selectedNode is set).
3. Do anything that appends nodes, the common one being the zoom-out load-more that fetches the next page. nodes.length goes up.
4. The effect re-runs, hits setSelectedNode(null), and the pinned popover disappears mid-read. It also fires a stray coolDown() on the simulation each time.

It is easy to miss because it only bites when there is a pinned selection and the node count changes in the same session, so a quick click-test without pagination looks fine. The PR keeps the active → inactive transition behaving exactly as before and only stops the no-op re-runs from clearing the selection.

If that repro holds up on your end, would you mind reopening? Happy to rebase onto the latest main first.