Fix hydration: effect was a no-op primitive, bytecode compiler emitted CALL_PRIM

Root cause: sx_primitives.ml registered "effect" as a native no-op (for SSR).
The bytecode compiler's (primitive? "effect") returned true, so it emitted
OP_CALL_PRIM instead of OP_GLOBAL_GET + OP_CALL. The VM's CALL_PRIM handler
found the native Nil-returning stub and never called the real effect function
from core-signals.sx.

Fix: Remove effect and register-in-scope from the primitives table. The server
overrides them via env_bind in sx_server.ml (after compilation), which doesn't
affect primitive? checks.

Also: VM CALL_PRIM now falls back to cek_call for non-NativeFn values (safety
net for any other functions that get misclassified).

15/15 source mode, 15/15 bytecode mode.

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

shared/static/wasm/sx/engine.sx

@@ -342,11 +342,16 @@
         (=
           (dom-get-attr old-node "data-sx-island")
           (dom-get-attr new-node "data-sx-island")))
-      (morph-island-children old-node new-node)
+      (do
+        (sync-attrs old-node new-node)
+        (morph-island-children old-node new-node))
       (or
         (not (= (dom-node-type old-node) (dom-node-type new-node)))
         (not (= (dom-node-name old-node) (dom-node-name new-node))))
-      (dom-replace-child (dom-parent old-node) (dom-clone new-node) old-node)
+      (dom-replace-child
+        (dom-parent old-node)
+        (dom-clone new-node true)
+        old-node)
       (or (= (dom-node-type old-node) 3) (= (dom-node-type old-node) 8))
       (when
         (not (= (dom-text-content old-node) (dom-text-content new-node)))
@@ -411,25 +416,37 @@
     (let
       ((old-kids (dom-child-list old-parent))
         (new-kids (dom-child-list new-parent))
-        (old-by-id
-          (reduce
-            (fn
-              ((acc :as dict) kid)
-              (let
-                ((id (let ((raw (dom-id kid))) (if (empty? raw) nil raw))))
-                (if id (do (dict-set! acc id kid) acc) acc)))
-            (dict)
-            old-kids))
-        (oi 0))
+        (old-by-id (dict))
+        (old-idx-by-id (dict))
+        (consumed (dict))
+        (oi 0)
+        (idx 0))
+      (for-each
+        (fn
+          (kid)
+          (let
+            ((id (dom-id kid)))
+            (when
+              (and id (not (empty? id)))
+              (dict-set! old-by-id id kid)
+              (dict-set! old-idx-by-id id idx)))
+          (set! idx (inc idx)))
+        old-kids)
       (for-each
         (fn
           (new-child)
           (let
-            ((match-id (let ((raw-id (dom-id new-child))) (if (empty? raw-id) nil raw-id)))
+            ((raw-id (dom-id new-child))
+              (match-id (if (and raw-id (not (empty? raw-id))) raw-id nil))
               (match-by-id (if match-id (dict-get old-by-id match-id) nil)))
             (cond
               (and match-by-id (not (nil? match-by-id)))
               (do
+                (let
+                  ((matched-idx (dict-get old-idx-by-id match-id)))
+                  (when
+                    matched-idx
+                    (dict-set! consumed (str matched-idx) true)))
                 (when
                   (and
                     (< oi (len old-kids))
@@ -443,20 +460,25 @@
               (< oi (len old-kids))
               (let
                 ((old-child (nth old-kids oi)))
-                (if
-                  (and (not (empty? (dom-id old-child))) (not match-id))
-                  (dom-insert-before
-                    old-parent
-                    (dom-clone new-child)
-                    old-child)
-                  (do (morph-node old-child new-child) (set! oi (inc oi)))))
-              :else (dom-append old-parent (dom-clone new-child)))))
+                (let
+                  ((old-id (dom-id old-child)))
+                  (if
+                    (and old-id (not (empty? old-id)) (not match-id))
+                    (dom-insert-before
+                      old-parent
+                      (dom-clone new-child true)
+                      old-child)
+                    (do
+                      (dict-set! consumed (str oi) true)
+                      (morph-node old-child new-child)
+                      (set! oi (inc oi))))))
+              :else (dom-append old-parent (dom-clone new-child true)))))
         new-kids)
       (for-each
         (fn
-          ((i :as number))
+          (i)
           (when
-            (>= i oi)
+            (not (dict-get consumed (str i)))
             (let
               ((leftover (nth old-kids i)))
               (when
@@ -465,7 +487,7 @@
                   (not (dom-has-attr? leftover "sx-preserve"))
                   (not (dom-has-attr? leftover "sx-ignore")))
                 (dom-remove-child old-parent leftover)))))
-        (range oi (len old-kids))))))
+        (range 0 (len old-kids))))))
 
 (define
   morph-island-children
@@ -588,7 +610,7 @@
           (morph-children target wrapper)))
       "outerHTML"
       (let
-        ((parent (dom-parent target)) (new-el (dom-clone new-nodes)))
+        ((parent (dom-parent target)) (new-el (dom-clone new-nodes true)))
         (if
           (dom-is-fragment? new-nodes)
           (let
@@ -596,7 +618,7 @@
             (if
               fc
               (do
-                (set! new-el (dom-clone fc))
+                (set! new-el (dom-clone fc true))
                 (dom-replace-child parent new-el target)
                 (let
                   ((sib (dom-next-sibling fc)))