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/tests/hygiene.sx

@@ -191,4 +191,30 @@
     (kh-eval-in "x" env))
   1)
 
+;; ── $let* — sequential let ──────────────────────────────────────
+(kh-test "let*: empty bindings"
+  (kh-eval-in "($let* () 42)" (kernel-standard-env)) 42)
+(kh-test "let*: single binding"
+  (kh-eval-in "($let* ((x 5)) (+ x 1))" (kernel-standard-env)) 6)
+(kh-test "let*: later sees earlier"
+  (kh-eval-in "($let* ((x 1) (y (+ x 1)) (z (+ y 1))) z)"
+              (kernel-standard-env)) 3)
+(kh-test "let*: bindings don't leak after"
+  (let ((env (kernel-standard-env)))
+    (kh-eval-in "($define! x 1)" env)
+    (kh-eval-in "($let* ((x 99) (y (+ x 1))) y)" env)
+    (kh-eval-in "x" env)) 1)
+(kh-test "let*: same-name later binding shadows earlier"
+  (kh-eval-in "($let* ((x 1) (x 2)) x)" (kernel-standard-env)) 2)
+(kh-test "let*: multi-expression body"
+  (kh-eval-in "($let* ((x 5)) ($define! double (+ x x)) double)"
+              (kernel-standard-env)) 10)
+(kh-test "let*: error on malformed binding"
+  (guard (e (true :raised))
+    (kh-eval-in "($let* ((x)) x)" (kernel-standard-env)))
+  :raised)
+(kh-test "let: multi-body"
+  (kh-eval-in "($let ((x 5)) ($define! tmp (+ x 1)) tmp)"
+              (kernel-standard-env)) 6)
+
 (define kh-tests-run! (fn () {:total (+ kh-test-pass kh-test-fail) :passed kh-test-pass :failed kh-test-fail :fails kh-test-fails}))