Reference const-expr closures through engine ids on PHP 8.6

CHANGELOG.md

@@ -39,6 +39,26 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   relied on the previous unconditional by-name behavior must pass the flag.
   Closures declared in constant expressions are unaffected.
 
+- Const-expr closures are referenced as `[class, "<site>@<rank>", line]` on
+  every PHP version: the id names the declaring reflection element (the class,
+  a constant, a property, a property hook or a method, parameters folded into
+  their method) and the closure's rank among the element's closures, in
+  evaluation order (attribute arguments first, nested const-expr surfaces
+  depth-first, then parameter defaults, then the constant or property default
+  value). The id equals the engine's own `getConstExprId()` for the sites the
+  engine addresses, and payloads produced on PHP 8.5, on PHP 8.6 and by the
+  polyfill are identical. On PHP 8.6 encoding uses the engine's non-evaluating
+  walk for anonymous closures and decoding tries `Closure::fromConstExpr()`
+  first, falling back to the evaluating walk (which alone covers constant and
+  property-default values). The previous site-based 5-element reference is
+  gone, with no backward compatibility: it never shipped in a release.
+- On PHP 8.6, first-class callables declared in a constant expression of another
+  class (`#[When(Validators::check(...))]`) or over a global function
+  (`#[When(strlen(...))]`) get their declaring class from the engine and
+  serialize as a (site-based) declaration-site reference with no
+  `allow_named_closures` opt-in -- the same payload the extension produces on
+  8.5 through ReflectionAttribute provenance, and that the polyfill produces.
+
 - On PHP 8.4+, `deepclone_from_array()` now creates object nodes whose
   payload slots or replayed `__unserialize` state carry a named-closure or
   const-expr-closure marker as