...aaaand I figured it out.

As long as the platform has ever requested Space Platform Foundation from the planet, it remains with a 0 in the construction requests, apparently. And while an item remains there, it will never be auto-dropped to the ground, even if the requests is 0.

Toggling "Auto ...

I have a space platform that makes a lot of Space Platform Foundation, to build itself.
However, that platform is done now, and keeps making Space Platform Foundation.
I wanted to put this to use, and requested it in my Cargo Landing Pad, to build other platforms with.

While other things the ...

Just posting my solution to this, in case someone else wants it. I'm using stack inserters to efficiently throw away excess from huge platforms.

Features:

A single constant combinator that defines what's supposed to be stored on the hub, and how much of each item is to be stored
Any excess ...

If you just want to select a signal, stick to it, and stop sending it when it's no longer present in the input, you don't need all of that.
This is what I use to throw away excess on my space platforms:

Screenshot 2025-02-23 143555.png

0eNrFV0tv2zAM/iuCLtsAtUgcO20NbLdil2GH7VgUhmIziVBZ8iS5XlD4v4 ...