psalm: Immutability/purity is not enforced in inheritance/contracts

Following example (https://psalm.dev/r/e5b578def2) is a clear violation of purity rules:

<?php

/** @psalm-immutable */
interface SomethingImmutable {
    public function someInteger() : int;
}

class MutableImplementation implements SomethingImmutable {
    private int $counter = 0;
    public function someInteger() : int {
        return ++$this->counter;
    }
}

/** @psalm-pure */
function useSomething(SomethingImmutable $something) : int
{
    return $something->someInteger();
}

$instance = new MutableImplementation;

echo useSomething($instance);
echo useSomething($instance);

Psalm does not find errors, but it should probably implicitly propagate @psalm-immutable to MutableImplementation, and flag it as an error.