nearestX ruleX sometimes disappears when parameter is a selection

[frtennis1]

I'm working with spec that is a simplified version of the normalized stocks example from the docs and seeing some unexpected behavior:

spec = {
    "plot": [
        {
            "mark": "lineY",
            "data": {"from": "df"},
            "x": "Date",
            "y": "AdjClose",
        },
        {"select": "nearestX", "as": "$point"},
        {"mark": "ruleX", "x": "$point"},
        {
            "mark": "textX",
            "text": "$point",
            "x": "$point",
            "frameAnchor": "top",
            "lineAnchor": "bottom",
            "dy": -7,
        },
    ],
    "yLabel": "AdjClose",
    "params": {"point": {"select": "crossfilter"}},
    # "params": {"point": {"date": "2015-01-01"}},
}

When $point is a Param, the ruleX is always visible even when the mouse leaves the plot area (desirable). HoweverX when $point is a selection, about half the time when the mouse leaves the plot area, the ruleX disappears. I think I can trigger the (undesirable) disappearing behavior more often when I move the mouse quickly.

(For context, for my purpose I'm trying to get the nearestX interactor to relay into another crossfilter while also being visually displayed with the ruleX, hence why I think I need to use a selection and not a Param)

[jheer]

Two things going on here:

1. There are currently some small semantic differences between Params and Selections in the nearest interactor implementation. I'll patch that up.
2. Whether or not a nearest selection "persists" when the mouse cursor goes far away is a function of the maxRadius parameter, which defaults to 40. If you set maxRadius to a large value (like 10000) you should be able to make the rule+label persist.

[jheer]

Differences between params and selections fixed by 9531916.