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).

test/chez/README.md

@@ -163,6 +163,28 @@ class names, eval-order, with-open — all deferred Phase-2 / dynamic-var gaps).
     The Chez host throws (Clojure-correct), so the 4 `odd arg …` corpus rows — which
     encode the seed's lenient behavior — sit in the crash bucket until the seed is
     fixed and those spec rows are updated to `:throws`.
+- inc 3q multimethod dispatch + late-bind (jolt-9ls5, Phase 2): `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 is set via a runtime
+  `chez-current-ns` (default "user"; the prelude load sets "clojure.core").
+
+  Two emit-side changes made this work:
+  - **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 makes an unresolved symbol lower to a
+    `var-ref` against the compile ns — the open-world semantics of `-e`. Set only by
+    the Chez `make-ctx`/`jolt-chez`; the main compiler keeps its strict behavior.
+  - a `:var` call head now routes through `jolt-invoke` (not a direct application),
+    since a late-bound var can hold a multifn (or a keyword/coll IFn), not just a
+    procedure. Transparent for procedures; the hot self-recursive call is a `:local`
+    known-proc, so it stays direct. (Class-based dispatch — `(class x)`/`String` — is
+    deferred; it needs the deftype/class subsystem.)
 
 The remaining buckets are the punch-list the next increments chase: ~361 emit-fail
 (genuine host interop — qualified Java/Janet refs, runtime `defmacro`/`eval`, out of