v0.3.0

Full detail lives in the docs and CHANGELOG.

⚠️ Breaking changes

• Variance markers are now out T / in T (was +T / -T) — rewrite +T → out T,
  -T → in T. Old source fails with a migration error. See variance.
• A final variant class is rejected — a covariant/contravariant class can't anchor the
  extends edge. Remove final from variant templates.
• Variant constructor params keep their real type (no longer erased to mixed), so
  construction is runtime-type-checked.

New features

• xphp check — validate-in-CI without emitting; collects every problem in one pass
  (text / json / github renderers) and runs your PHPStan over the compiled output.
• compile gates by default — runs the same validators + PHPStan before emitting;
  --no-check for a fast iteration build.
• Closure(...) signature types — typed-closure hints, conformance-checked and erased to
  \Closure. See closure types.
• xphp.json manifest — declare source roots / output / hash length for multi-root builds.
• Element-typed methods on covariant collections — a method-generic bound grounded on the
  enclosing class parameter (contains<U : E>). See type bounds.
• Generic methods through inheritance — turbofish on a subclass receiver (instance, static,
  nullsafe); an unresolved turbofish is now a compile error.
• Variance refinements — out T / in T on private properties; by-reference params are
  invariant.

Bug fixes

• Turbofish on an undeterminable receiver is rejected instead of emitting a runtime fatal.
• A sibling-referencing class bound (class Pair<T, U : T>) is grounded correctly.
• A scalar bound (int, string, …) is no longer flagged as an undeclared type.