Mistune directives/include: mutual `.. include::` recursion crashes the renderer with `RecursionError`, denial of service via two attacker-controlled markdown files

Summary Type: Uncontrolled recursion via mutual include. The Include directive checks for direct self-reference a.md cannot include a.md, but does not detect indirect cycles. Two markdown files that include each other a.md → includes b.md → includes a.md cause unbounded recursion until Python's...