[Python] How to link selection across marks/symbols in Altair?

Imagine we have an Altair graph in Python like:

import altair as alt
from vega_datasets import data

cars = data.cars.url

selector = alt.selection_point()
conditional = alt.when(selector).then("Origin:N").otherwise(alt.value("lightgray"))

base = alt.Chart(cars).encode(
x="Horsepower:Q",
y="Miles_per_Gallon:Q",
)

points = base.mark_point().encode(color=conditional).add_params(selector)
lines = base.mark_line().encode(color=conditional)

(points + lines).properties(width=600, height=300).interactive()


which gives the graph:



Currently, when selecting the points, all other points and all the lines go gray. But, is there a way to ensure that the selected point and the whole connecting line and points are both highlighted too?

I've been scouring the docs on this for a while and haven't quite worked it out. All my attempts have kept the selection separate, not shared across the different marks/symbols. I'm looking for some concept of the selector being 'shared' across the different layers.

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