Expand WASM browser tests: 28 SX deftest forms

Added 13 new tests covering:
- Signal core: create, reset!, swap!, computed, effect re-run,
  effect cleanup, batch
- DOM extended: nested elements, boolean attrs, nil attrs, multiple
  children, HTML/DOM output match
- Reactive attrs: initial value, signal updates, nil removal,
  multiple attrs on same element, multi-token spread
- Island scope: scope detection, disposer collection, context
  visibility, defcomp rendering
- Conditional: if/when/cond/let/begin in render-to-dom

28/28 source, 28/28 bytecode.

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

web/tests/test-wasm-browser.sx

@@ -168,6 +168,127 @@
           "outerHTML")
         "sx-text-center"))))
 
+(defsuite
+  "wasm-signals-core"
+  (deftest "signal create and deref" (assert-equal 42 (deref (signal 42))))
+  (deftest
+    "reset! changes value"
+    (let
+      ((s (signal "old")))
+      (reset! s "new")
+      (assert-equal "new" (deref s))))
+  (deftest
+    "swap! applies function"
+    (let ((s (signal 10))) (swap! s + 5) (assert-equal 15 (deref s))))
+  (deftest
+    "computed derives from signal"
+    (let
+      ((s (signal 3)))
+      (let
+        ((c (computed (fn () (* (deref s) 2)))))
+        (assert-equal 6 (deref c)))))
+  (deftest
+    "effect runs immediately"
+    (let
+      ((log (list)))
+      (effect (fn () (append! log "ran")))
+      (assert-equal 1 (len log))))
+  (deftest
+    "effect re-runs on signal change"
+    (let
+      ((log (list)) (s (signal "a")))
+      (effect (fn () (append! log (deref s))))
+      (reset! s "b")
+      (assert-equal 2 (len log))
+      (assert-equal "b" (nth log 1))))
+  (deftest
+    "effect cleanup called on re-run"
+    (let
+      ((log (list)) (s (signal 1)))
+      (effect
+        (fn
+          ()
+          (let
+            ((v (deref s)))
+            (append! log (str "run:" v))
+            (fn () (append! log (str "cleanup:" v))))))
+      (reset! s 2)
+      (assert-true (contains? log "cleanup:1"))))
+  (deftest
+    "batch delays notification"
+    (let
+      ((count 0) (s (signal 0)))
+      (effect (fn () (deref s) (set! count (+ count 1))))
+      (batch (fn () (reset! s 1) (reset! s 2) (reset! s 3)))
+      (assert-equal 2 count))))
+
+(defsuite
+  "wasm-conditional-rendering"
+  (deftest
+    "if renders then branch"
+    (assert-true
+      (contains?
+        (host-get
+          (let
+            ((d (list)))
+            (with-island-scope
+              (fn (x) (append! d x))
+              (fn
+                ()
+                (render-to-dom
+                  (quote (if true (div "yes") (div "no")))
+                  (global-env)
+                  nil))))
+          "outerHTML")
+        "yes")))
+  (deftest
+    "when renders body on true"
+    (assert-true
+      (contains?
+        (host-get
+          (let
+            ((d (list)))
+            (with-island-scope
+              (fn (x) (append! d x))
+              (fn
+                ()
+                (render-to-dom
+                  (quote (when true (div "visible")))
+                  (global-env)
+                  nil))))
+          "outerHTML")
+        "visible")))
+  (deftest
+    "cond selects correct branch"
+    (assert-true
+      (contains?
+        (host-get
+          (render-to-dom
+            (quote (cond false (div "a") true (div "b") :else (div "c")))
+            (global-env)
+            nil)
+          "outerHTML")
+        "b")))
+  (deftest
+    "render-to-dom with let bindings"
+    (assert-true
+      (contains?
+        (host-get
+          (render-to-dom
+            (quote (let ((x "hello")) (div x)))
+            (global-env)
+            nil)
+          "outerHTML")
+        "hello")))
+  (deftest
+    "render-to-dom with begin"
+    (assert-true
+      (contains?
+        (host-get
+          (render-to-dom (quote (do (div "only-this"))) (global-env) nil)
+          "outerHTML")
+        "only-this"))))
+
 (defsuite
   "wasm-signal-propagation"
   (deftest