v0.13.0

• Fixed. A schema that refers to itself — a tree whose children are
  trees, a comment thread, a nested error — can be loaded. Every $ref was
  inlined, so a self-reference expanded until the depth guard tripped and the
  document was refused as $ref chain is too deep (possible circular reference). The members of a reference cycle are now kept as the Schema
  Object's $defs, named after their JSON Pointer
  (#/components/schemas/Node → components.schemas.Node, a.json:Node from
  another file), and the reference back to one becomes a local
  {$ref: '#/$defs/…'} carrying the target's type — the form the validation
  backend evaluates natively; the schema the cycle starts from is inlined
  where it is first met and kept as a def as well. The directional
  readOnly/writeOnly rewrite (SchemaCheck::effective()) reaches into
  $defs, so a readOnly member of a tree node is not required at any depth
  of a request. A schema without a cycle compiles exactly as before, with no
  $defs; a cycle outside a schema (a Path Item or Response reaching itself)
  and a cycle with no schema in it (A: {$ref: B}, B: {$ref: A}) stay
  refused, now by name. The cycle is found before the depth is charged, so a
  cycle at the end of a long chain is a cycle, not a deep chain, and the
  depth message drops its "(possible circular reference)". (#159)
• Fixed. {} in a subschema position — items: {}, properties: {x: {}}, additionalProperties: {} — was refused as a list where a schema was
  expected: the empty object decodes to the empty array, which
  array_is_list() calls a list. It is the schema with no keywords, admits
  everything, and now goes back on the wire as {}; so does a schema that
  normalizes down to nothing, such as OAS 3.0's {nullable: true}, which the
  backend used to reject as []. GitHub's published REST description
  declares both shapes.
• Added. Limits::$resolvedNodes (default 1 000 000): the
  reference-resolution budget was a constant of 100 000 inside the resolver,
  absent from Limits while the README listed it among the budgets, and a
  large flat document tripped it with no way to raise it. A shared component
  is visited once per use, so a description costs more resolution than it
  has nodes — GitHub's REST API (1 239 operations, 13 MB) needs about 360 000,
  and loads with documentBytes raised. Stripe's spec3.json still does
  not: its components form a DAG that inlining expands past twenty million
  nodes for a single schema, which is a different limitation, tracked
  separately.
• Changed. A 3.1 schema reference that is an alias of another
  (a: {$ref: b}) lifts type, items and properties to the top of the
  conjunction it forms with its siblings, as a direct reference always did;
  the chain is resolved to its end before the merge.