Beware Of findFirst() And findAny()

Using `findFirst()` or `findAny()` after filtering a Java 8 Stream implicitly assumes at most one element matches, but this assumption is never enforced. If multiple elements pass the filter, the code silently returns just one, potentially causing hard-to-detect bugs. A safer alternative is using `reduce()` with a custom accumulator that throws an exception when a second element is encountered. A reusable `toOnlyElement()` utility method can be extracted to make the intent explicit. The trade-off is that unlike `findFirst()`/`findAny()`, this approach is not short-circuiting and will traverse the entire stream unless a duplicate is found early.