Fix named-let set! scoping + convert test to deftest

Named let's sf-named-let used call-lambda which returns a thunk that
was never trampolined. The body executed in a disconnected env, so
set! couldn't reach outer let bindings. Fixed by using cek-call which
evaluates through the full CEK machine with proper env chain.

Also converted test-named-let-set.sx from assert= (uses broken = for
lists) to deftest/assert-equal (uses deep equal?).

JS standard: 1120/1120, JS full: 1600/1600. Zero failures.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

shared/static/scripts/sx-browser.js

@@ -24,7 +24,7 @@
   // =========================================================================
 
   var NIL = Object.freeze({ _nil: true, toString: function() { return "nil"; } });
-  var SX_VERSION = "2026-03-31T10:16:31Z";
+  var SX_VERSION = "2026-03-31T21:28:15Z";
 
   function isNil(x) { return x === NIL || x === null || x === undefined; }
   function isSxTruthy(x) { return x !== false && !isNil(x); }
@@ -422,7 +422,7 @@
   PRIMITIVES["len"] = function(c) { return Array.isArray(c) ? c.length : typeof c === "string" ? c.length : Object.keys(c).length; };
   PRIMITIVES["first"] = function(c) { return c && c.length > 0 ? c[0] : NIL; };
   PRIMITIVES["last"] = function(c) { return c && c.length > 0 ? c[c.length - 1] : NIL; };
-  PRIMITIVES["rest"] = function(c) { if (c && typeof c.slice !== "function") { console.error("[sx-debug] rest called on non-sliceable:", typeof c, c, new Error().stack); return []; } return c ? c.slice(1) : []; };
+  PRIMITIVES["rest"] = function(c) { if (!c || c._nil) return []; if (typeof c.slice !== "function") return []; return c.slice(1); };
   PRIMITIVES["nth"] = function(c, n) { return c && n >= 0 && n < c.length ? c[n] : NIL; };
   PRIMITIVES["cons"] = function(x, c) { return [x].concat(c || []); };
   PRIMITIVES["append"] = function(c, x) { return (c || []).concat(Array.isArray(x) ? x : [x]); };
@@ -1366,7 +1366,7 @@ return append_b(inits, nth(binding, 1)); }, bindings) : reduce(function(acc, pai
   envBind(lambdaClosure(loopFn), loopName, loopFn);
   return (function() {
   var initVals = map(function(e) { return trampoline(evalExpr(e, env)); }, inits);
-  return callLambda(loopFn, initVals, env);
+  return cekCall(loopFn, initVals);
 })();
 })();
 })(); };
@@ -6683,7 +6683,7 @@ PRIMITIVES["batch"] = batch;
 PRIMITIVES["notify-subscribers"] = notifySubscribers;
 
   // flush-subscribers
-  var flushSubscribers = function(s) { return forEach(function(sub) { return sub(); }, signalSubscribers(s)); };
+  var flushSubscribers = function(s) { return forEach(function(sub) { return cekCall(sub, NIL); }, signalSubscribers(s)); };
 PRIMITIVES["flush-subscribers"] = flushSubscribers;
 
   // dispose-computed

spec/evaluator.sx

@@ -544,7 +544,7 @@
         (env-bind! (lambda-closure loop-fn) loop-name loop-fn)
         (let
           ((init-vals (map (fn (e) (trampoline (eval-expr e env))) inits)))
-          (call-lambda loop-fn init-vals env))))))
+          (cek-call loop-fn init-vals))))))
 
 (define
   sf-lambda

spec/tests/test-named-let-set.sx

@@ -1,52 +1,38 @@
-(assert=
+(defsuite "named-let-set"
-  (let ((x 0)) (let loop () (when (< x 5) (set! x (+ x 1)) (loop))) x)
+  (deftest "set! counter in named let loop"
-  5
+    (assert-equal 5
-  "set! counter in named let loop")
+      (let ((x 0)) (let loop () (when (< x 5) (set! x (+ x 1)) (loop))) x)))
 
-(assert=
+  (deftest "set! list accumulator in named let with param"
-  (let
+    (assert-equal (list 0 1 2)
-    ((acc (list)))
+      (let ((acc (list)))
-    (let
+        (let loop ((i 0))
-      loop
-      ((i 0))
           (when (< i 3) (set! acc (append acc (list i))) (loop (+ i 1))))
-    acc)
+        acc)))
-  (list 0 1 2)
-  "set! list accumulator in named let with param")
 
-(assert=
+  (deftest "append! + set! counter in named let"
-  (let
+    (assert-equal (list 0 1 2)
-    ((acc (list)) (i 0))
+      (let ((acc (list)) (i 0))
         (let loop () (when (< i 3) (append! acc i) (set! i (+ i 1)) (loop)))
-    acc)
+        acc)))
-  (list 0 1 2)
-  "append! + set! counter in named let")
 
-(assert=
+  (deftest "set! sum in named let loop (1..10)"
-  (let
+    (assert-equal 55
-    ((sum 0))
+      (let ((sum 0))
-    (let
+        (let loop ((i 1))
-      loop
-      ((i 1))
           (when (<= i 10) (set! sum (+ sum i)) (loop (+ i 1))))
-    sum)
+        sum)))
-  55
-  "set! sum in named let loop (1..10)")
 
-(assert=
+  (deftest "set! string accumulator in named let"
-  (let
+    (assert-equal "012"
-    ((result ""))
+      (let ((result ""))
-    (let
+        (let loop ((i 0))
-      loop
-      ((i 0))
           (when (< i 3) (set! result (str result (str i))) (loop (+ i 1))))
-    result)
+        result)))
-  "012"
-  "set! string accumulator in named let")
 
-(assert= (let ((x 0)) (set! x 42) x) 42 "set! in plain let (baseline)")
+  (deftest "set! in plain let (baseline)"
+    (assert-equal 42 (let ((x 0)) (set! x 42) x)))
 
-(assert=
+  (deftest "named let without set! (baseline)"
-  (let loop ((i 0) (acc 0)) (if (< i 5) (loop (+ i 1) (+ acc i)) acc))
+    (assert-equal 10
-  10
+      (let loop ((i 0) (acc 0)) (if (< i 5) (loop (+ i 1) (+ acc i)) acc)))))
-  "named let without set! (baseline)")