Is there in English language an expression/idiom that reflects the idea that we make something vulnerable to be attacked because we want to trap the attacker ?
The term honey pot is often used for this.
A sweet, tempting attraction to trap an attacker.
You may also find the word "bait" useful, as in "to bait someone" or "baiting someone", although recent usage has changed it somewhat to mean "to provoke someone into reacting (often excessively and to their own disadvantage)".
"Feigned retreat" may be useful in some contexts, but this connotes that open conflict has already begun.