"fuse" implies that the CPU will stop working when it is overclocked, this seems to be more of a mechanism for AMD to let them know that the reason the CPU is not working anymore is because it was overclocked and fried.
All this fuse does is tell AMD that the chip has had custom clocks or voltage applied to it (this appears to also apply to underclocking and undervolting as far as I can gather)
It does not prove that if the chip is faulty that it must be the OC/undervolt/whatever that caused it.
Think of those water detection strips in other products. They can tell the manufacturer if something has been in a humid environment, but just because it has been doesn't guarantee that that is what caused the fault to come about.
That was years ago, the phones have been waterproof for a long time- I would certainly file a warranty complaint with Apple if my waterproof iPhone was damaged from humid air, rain, falling in the tub as it’s rated to survive all those things. In fact, 5+ years ago people were doing tests dropping phones down 30 feet under water and bringing them up just fine.
Laptops on the other hand are not rated for water, and you’re right, a laptop full of purple spill sensors gets denied unless you bitch hard enough.
No, this means something else in chip design. For example, an AVR microcontroller can be configured by blowing some fuses. Here is an introduction: https://www.ladyada.net/learn/avr/fuses.html
Understandable but this is not a fuse in common usage of the word, which is used to break a circuit to protect against over-current. Rather it's an part that changes state irreversibly (much like a fuse would) when something happens. There is no implication that it would cut off the power to the CPU in this sense.
But in the world of electronics fuses and circuit breakers exist to trip when too much voltage is applied to protect the circuit. That's their generally agreed upon definition.
A fuse is just an electronic component. It can be used for circuit protection, but it doesn't have to be. For example, a transistor doesn't have to be an amplifier, a resistor doesn't have to be for dimming bulbs, etc.