fix: ensure unowned deriveds can add themselves as reactions while connected

[dummdidumm]

Fixes #15829 and potentially #15853

I can't quite articulate yet why this is right, but I think it is. Basically, an unowned derived should still add itself as a reaction while it is properly connected, which means it can be cleaned up correctly - and this connection is indicated by it having reactions.

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[paoloricciuti]

Is the name of the test correct? Isn't the change that we actually add the derived as a reaction? I think it makes sense: the problem is probably that we check if the derived is UNOWNED before executing it so if the execution changes that (connecting it) when we reach the point of the code you changes skip_reaction should be false (because now the derived it's not unowned anymore) but it's still true and you can check that by looking if it has reactions (or i suppose we could also check if (reaction.f & UNOWNED) !== 0 in line?)

[paoloricciuti]

Btw scratch the last sentence, I confused it and also the flag is never set to false

[paoloricciuti]

I tried to spend the whole day to figure out if there was a different way we could get the hint that "this unowned derived can be cleared so add it anyway" and i couldn't...but I think the important bit is that it works and doesn't leak reactions...so i would say let's go with it?

[paoloricciuti]

I tried to spend the whole day to figure out if there was a different way we could get the hint that "this unowned derived can be cleared so add it anyway" and i couldn't...but I think the important bit is that it works and doesn't leak reactions...so i would say let's go with it?

[paoloricciuti]

I tried to spend the whole day to figure out if there was a different way we could get the hint that "this unowned derived can be cleared so add it anyway" and i couldn't...but I think the important bit is that it works and doesn't leak reactions...so i would say let's go with it?