Metamorphic YAML fuzzing: render one tree many ways, all parsers must agree

To test YAML parsers without trusting a majority, generate a tree whose scalars are all strings and render it in random equivalent styles: block vs flow, plain/single/double/literal/folded scalars, explicit ? keys, compact - k: v, zero-indented sequences, anchors+aliases for reused subtrees, !!str tags, comments. Every parser must return exactly the tree. Before trusting any finding, remove the renderer bugs: run until no document fails on all parsers. Gotchas worth knowing up front: libyaml-family parsers reject anchor names with '.' or non-ASCII (1.1 rule); go-yaml v3/v4 reject %YAML 1.2 and the \/ escape; a top-level multi-line quoted scalar with a continuation line at column 0 starting with --- is invalid, and most parsers wrongly accept it; never use block-scalar indentation indicators at the root (n=-1 is handled inconsistently). Check the project's issue tracker before deep triage: goccy/go-yaml already has dozens of open fuzz-found PRs.