Chez Phase 1 (increment 3q): multimethod dispatch + late-bind

host/chez/multimethods.ss implements the multimethod runtime: defmulti/defmethod
expand to defmulti-setup/defmethod-setup calls (+ get-method/methods/
remove-method/prefer-method/prefers). A jolt-multifn record carries its dispatch
fn and a jolt=-keyed method table; jolt-invoke dispatches it (exact match, then
isa?/hierarchy with prefer-method, then :default), reusing the overlay's
isa?/derive/make-hierarchy. The multifn's ns comes from a runtime chez-current-ns
(default user; the prelude load sets clojure.core for print-method/print-dup).

Two emit-side changes were needed:
- late-bind (:late-bind-unresolved? ctx flag, default OFF): defmulti expands to a
  bare-symbol setup call, so the analyzer doesn't intern the name and a forward
  reference '(area ...)' after '(defmulti area ...)' in one form was 'Unable to
  resolve symbol'. The strict compiler punts these to the interpreter; the Chez
  back end has none, so the flag lowers an unresolved symbol to a var-ref against
  the compile ns (open-world -e semantics). Set only by the Chez make-ctx /
  jolt-chez; the main compiler keeps strict resolution (host_iface late-bind?
  defaults nil).
- a :var call head now routes through jolt-invoke, since a late-bound var can hold
  a multifn (or keyword/coll IFn), not just a procedure. Transparent for
  procedures; the hot self-recursive call is a :local known-proc, stays direct.

Class-based dispatch ((class x)/String) deferred (needs deftype/class subsystem).

Parity 1506 -> 1530/2497, 0 new divergences. emit-test 302/302. Full janet gate
green (the analyzer flag is off there; suite flakiness under parallel load only).

jolt-core/jolt/analyzer.clj

@@ -24,7 +24,7 @@
                                form-regex? form-regex-source
                                form-macro? form-expand-1 resolve-global
                                form-sym-meta host-intern! form-syntax-quote-lower
-                               record-type? record-ctor-key form-position]]))
+                               record-type? record-ctor-key form-position late-bind?]]))
 
 (declare analyze)
 
@@ -317,7 +317,13 @@
                 ;; (defmulti's setup call) legitimately reference the var they
                 ;; are about to create when nested in a non-top-level do. Real
                 ;; forward references want (declare ...), as in Clojure.
-                (uncompilable (str "Unable to resolve symbol: " nm " in this context")))))))
+                ;; Under late-bind? (the Chez back end, which has no interpreter
+                ;; to punt to) an unresolved symbol instead lowers to a var-ref
+                ;; against the compile ns — resolved at runtime, the open-world
+                ;; semantics of -e — so defmulti/defmethod forward references work.
+                (if (late-bind? ctx)
+                  (var-ref (compile-ns ctx) nm)
+                  (uncompilable (str "Unable to resolve symbol: " nm " in this context"))))))))
 
 (defn- analyze-list [ctx form env]
   (let [items (vec (form-elements form))]