Leetcode 3504. Longest Palindrome After Substring Concatenation II

Given strings s and t, pick any substring of s and any substring of t, concatenate them in order, and return the length of the longest palindrome obtainable. The core challenge is efficiently handling palindromes that may lie entirely in one string or span the s/t boundary by matching characters from s with mirrored characters from t (n ≤ 1000).