kernel: $let* sequential let + multi-body $let + 8 tests [nothing]

$let* nests env-extensions one per binding — each binding sees earlier
ones. $let now also accepts multi-expression bodies. 260 tests total.

lib/kernel/runtime.sx

@@ -572,14 +572,47 @@
   (kernel-make-primitive-operative
     (fn (args dyn-env)
       (cond
-        ((not (= (length args) 2))
-          (error "$let: expects (bindings body)"))
+        ((< (length args) 2)
+          (error "$let: expects (bindings body...)"))
         ((not (list? (first args)))
           (error "$let: bindings must be a list"))
         (:else
           (let ((local (kernel-extend-env dyn-env)))
             (knl-bind-let-vals! local (first args) dyn-env)
-            (kernel-eval (nth args 1) local)))))))
+            (knl-eval-body (rest args) local)))))))
+
+;; $let* — sequential let. Each binding sees prior names in scope.
+;; Implemented by nesting envs one per binding; the body runs in the
+;; innermost env, so later bindings shadow earlier ones if names repeat.
+(define knl-let*-step
+  (fn (bindings env body-forms)
+    (cond
+      ((or (nil? bindings) (= (length bindings) 0))
+        (knl-eval-body body-forms env))
+      (:else
+        (let ((b (first bindings)))
+          (cond
+            ((not (and (list? b) (= (length b) 2)))
+              (error "$let*: each binding must be (name expr)"))
+            ((not (string? (first b)))
+              (error "$let*: binding name must be a symbol"))
+            (:else
+              (let ((child (kernel-extend-env env)))
+                (kernel-env-bind! child
+                                  (first b)
+                                  (kernel-eval (nth b 1) env))
+                (knl-let*-step (rest bindings) child body-forms)))))))))
+
+(define kernel-let*-operative
+  (kernel-make-primitive-operative
+    (fn (args dyn-env)
+      (cond
+        ((< (length args) 2)
+          (error "$let*: expects (bindings body...)"))
+        ((not (list? (first args)))
+          (error "$let*: bindings must be a list"))
+        (:else
+          (knl-let*-step (first args) dyn-env (rest args)))))))
 
 (define kernel-define-in!-operative
   (kernel-make-primitive-operative
@@ -646,5 +679,6 @@
       (kernel-env-bind! env "make-encapsulation-type"
                             kernel-make-encap-type-applicative)
       (kernel-env-bind! env "$let"         kernel-let-operative)
+      (kernel-env-bind! env "$let*"        kernel-let*-operative)
       (kernel-env-bind! env "$define-in!"  kernel-define-in!-operative)
       env)))