jolt build: --opt mode turns on the inference passes (Phase 4 stage 4a)

Wire the optimization gate to build mode. inline-enabled? (which gates the
inference + flatten-lets + scalar-replace passes in jolt.passes/run-passes) was
hardwired off, so those passes had never run on Chez at all. host-contract now
exposes a settable hc-optimize? flag; `jolt build --opt` flips it on during app
emission.

Kept off for the default release build for now: the passes are sound by design
(RFC 0005/0006) but unexercised on Chez, so release stays on the proven
var-deref codegen until they're validated against the corpus. --opt is the
opt-in fast path. buildsmoke checks both modes produce the same result.

This does not yet deliver direct call binding — the backend has no direct-link
emission path (every :var call still routes through jolt-invoke/var-deref) and
the inline-ir host stash is still a stub. Those are the remaining stage-4 levers.

host/chez/build-smoke.sh

@@ -22,11 +22,22 @@ want='HELLO FROM A BUILT BINARY!
 HELLO FROM A BUILT BINARY!
 args: [alpha bb ccc]
 sum: 10'
-if [ "$got" = "$want" ]; then
-  echo "build smoke: passed"
-else
+if [ "$got" != "$want" ]; then
   echo "  FAIL: binary output mismatch"
   echo "--- want ---"; echo "$want"
   echo "--- got ----"; echo "$got"
   exit 1
 fi
+
+# Optimized mode (inference + flatten + scalar-replace) must produce the same
+# result — a sanity check that the passes don't miscompile this app.
+if ! JOLT_PWD="$app" bin/joltc build -m app.core -o "$out" --opt >/dev/null 2>&1; then
+  echo "  FAIL: jolt build --opt exited non-zero"; exit 1
+fi
+got_opt="$(cd / && "$out" alpha bb ccc 2>&1)"
+if [ "$got_opt" != "$want" ]; then
+  echo "  FAIL: --opt binary output mismatch"
+  echo "--- got ----"; echo "$got_opt"
+  exit 1
+fi
+echo "build smoke: passed (release + optimized)"

host/chez/build.ss

@@ -179,10 +179,15 @@
       (when (null? ordered)
         (error 'jolt-build (string-append "no source namespace loaded for " entry-ns
                                           " — is it on the source roots?")))
-      ;; 2. emit each app namespace.
+      ;; 2. emit each app namespace. `optimized` turns on the inference + flatten
+      ;; + scalar-replace passes (closed world). release/dev stay on proven
+      ;; var-deref codegen until those passes are validated on Chez — they were
+      ;; dormant before `jolt build` (inline-enabled? was hardwired off).
+      (set-optimize! (string=? mode "optimized"))
       (let* ((app-strs (apply append
                          (map (lambda (nf) (bld-emit-ns (car nf) (read-file-string (cdr nf))))
                               ordered)))
+             (_ (set-optimize! #f))
              (builddir (string-append out-path ".build"))
              (flat-ss  (string-append builddir "/flat.ss"))
              (flat-so  (string-append builddir "/flat.so"))

host/chez/host-contract.ss

@@ -280,7 +280,12 @@
 (define (hc-record-type? ctx name) #f)
 (define (hc-record-ctor-key ctx name) jolt-nil)
 (define (hc-record-shapes ctx) (jolt-hash-map))
-(define (hc-inline-enabled? ctx) #f)
+;; Optimization gate. Off for ordinary runs (open world, redefinition); `jolt
+;; build` flips it on during app emission for release/optimized modes (closed
+;; world), turning on the inference + flatten + scalar-replace passes.
+(define hc-optimize? #f)
+(define (set-optimize! on) (set! hc-optimize? on))
+(define (hc-inline-enabled? ctx) hc-optimize?)
 (define (hc-inline-ir ctx ns-name nm) jolt-nil)
 
 ;; --- declare the hot clojure.core primitives so resolve-global sees them ------