I'm not making a deep point; everything which is separate has a way of enforcing inside vs outside. Some are robust (fort knox). Others are temporary, diffuse and don't hang around (a fart). Some have instruction content to help enforce their boundaries (i.e. DNA, a computer program, or the army corps of engineers manual).
At the point where an object ceases to use pure physics and starts to use information to defend its boundary, the rejection of non-self is often acquired early on. (with obvious selection bias).
If you want to rule out any supernatural stuff, you model it as: the cereal box is part of a system that includes general mills, kids like you, and this grrrreat breakfast. Most of the information content of the system is at general mills (infectious) and the consumer (defense). Tony the tiger is a plot to play kids against adults and get those boxes into households. So is putting the boxes on the bottom shelf at supermarkets.
The even creepier view is that the cereal box has some independent existence and the box is gaming general mills to propagate its existence.
Before you object that the information content and reproductive machine of the box are external, consider a sperm cell or a seed pod. Neither of these has the full information of its system; neither is self-serving. Sexual reproduction also means that in normal practice (ignoring lizards and parthenogenesis), no individual has the full machinery of the species.
Note: I'm not ascribing intellect, intention or consciousness to any of these objects. Just drawing the boundaries of information in convenient places. It's not crazy to say that a cereal box exists as a separate thing. Once you say that, you have to consider whether it exists separately from general mills (it does, other companies use it).
Your process hangup, evolved vs coalesced vs designed, is an important distinction and may bias the sorts of forms that emerge. Evolved and designed end up being similar; both are shaking up information particles until something emerges that can propogate itself. Thomas Edison set out to design a light-bulb but he didn't set out to be born as thomas edison; the ball was rolling down the hill when he started. Not to take away from people's inventions, but if you compare across 100 alien worlds, maybe there are patterns about when the lightbulb is invented, and most worlds do it after certain other pieces are in place.
Another example is the eye: this is an evolutionary form that shows up when pigments and neurons are in the genome but something more is needed. A wire gets crossed and there is no turning back.