Unify scoped effects: scope as general primitive, provide as sugar

- Add `scope` special form to eval.sx: (scope name body...) or
  (scope name :value v body...) — general dynamic scope primitive
- `provide` becomes sugar: (provide name value body...) calls scope
- Rename provide-push!/provide-pop! to scope-push!/scope-pop! throughout
  all adapters (async, dom, html, sx) and platform implementations
- Update boundary.sx: Tier 5 now "Scoped effects" with scope-push!/
  scope-pop! as primary, provide-push!/provide-pop! as aliases
- Add scope form handling to async adapter and aser wire format
- Update sx-browser.js, sx_ref.py (bootstrapped output)
- Add scopes.sx docs page, update provide/spreads/demo docs
- Update nav-data, page-functions, docs page definitions

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

shared/sx/ref/adapter-html.sx

@@ -56,7 +56,7 @@
   (list "if" "when" "cond" "case" "let" "let*" "begin" "do"
         "define" "defcomp" "defisland" "defmacro" "defstyle" "defhandler"
         "deftype" "defeffect"
-        "map" "map-indexed" "filter" "for-each" "provide"))
+        "map" "map-indexed" "filter" "for-each" "scope" "provide"))
 
 (define render-html-form? :effects []
   (fn ((name :as string))
@@ -229,18 +229,38 @@
                   (render-to-html (apply f (list item)) env)))
               coll)))
 
-      ;; provide — render-time dynamic scope
+      ;; scope — unified render-time dynamic scope
+      (= name "scope")
+        (let ((scope-name (trampoline (eval-expr (nth expr 1) env)))
+              (rest-args (slice expr 2))
+              (scope-val nil)
+              (body-exprs nil))
+          ;; Check for :value keyword
+          (if (and (>= (len rest-args) 2)
+                   (= (type-of (first rest-args)) "keyword")
+                   (= (keyword-name (first rest-args)) "value"))
+            (do (set! scope-val (trampoline (eval-expr (nth rest-args 1) env)))
+                (set! body-exprs (slice rest-args 2)))
+            (set! body-exprs rest-args))
+          (scope-push! scope-name scope-val)
+          (let ((result (if (= (len body-exprs) 1)
+                          (render-to-html (first body-exprs) env)
+                          (join "" (map (fn (e) (render-to-html e env)) body-exprs)))))
+            (scope-pop! scope-name)
+            result))
+
+      ;; provide — sugar for scope with value
       (= name "provide")
         (let ((prov-name (trampoline (eval-expr (nth expr 1) env)))
               (prov-val (trampoline (eval-expr (nth expr 2) env)))
               (body-start 3)
               (body-count (- (len expr) 3)))
-          (provide-push! prov-name prov-val)
+          (scope-push! prov-name prov-val)
           (let ((result (if (= body-count 1)
                           (render-to-html (nth expr body-start) env)
                           (join "" (map (fn (i) (render-to-html (nth expr i) env))
                                        (range body-start (+ body-start body-count)))))))
-            (provide-pop! prov-name)
+            (scope-pop! prov-name)
             result))
 
       ;; Fallback
@@ -314,12 +334,12 @@
         (str "<" tag (render-attrs attrs) " />")
         ;; Provide scope for spread emit!
         (do
-          (provide-push! "element-attrs" nil)
+          (scope-push! "element-attrs" nil)
           (let ((content (join "" (map (fn (c) (render-to-html c env)) children))))
             (for-each
               (fn (spread-dict) (merge-spread-attrs attrs spread-dict))
               (emitted "element-attrs"))
-            (provide-pop! "element-attrs")
+            (scope-pop! "element-attrs")
             (str "<" tag (render-attrs attrs) ">"
               content
               "</" tag ">")))))))
@@ -359,12 +379,12 @@
         args)
       ;; Provide scope for spread emit!
       (let ((lake-attrs (dict "data-sx-lake" (or lake-id ""))))
-        (provide-push! "element-attrs" nil)
+        (scope-push! "element-attrs" nil)
         (let ((content (join "" (map (fn (c) (render-to-html c env)) children))))
           (for-each
             (fn (spread-dict) (merge-spread-attrs lake-attrs spread-dict))
             (emitted "element-attrs"))
-          (provide-pop! "element-attrs")
+          (scope-pop! "element-attrs")
           (str "<" lake-tag (render-attrs lake-attrs) ">"
                content
                "</" lake-tag ">"))))))
@@ -407,12 +427,12 @@
         args)
       ;; Provide scope for spread emit!
       (let ((marsh-attrs (dict "data-sx-marsh" (or marsh-id ""))))
-        (provide-push! "element-attrs" nil)
+        (scope-push! "element-attrs" nil)
         (let ((content (join "" (map (fn (c) (render-to-html c env)) children))))
           (for-each
             (fn (spread-dict) (merge-spread-attrs marsh-attrs spread-dict))
             (emitted "element-attrs"))
-          (provide-pop! "element-attrs")
+          (scope-pop! "element-attrs")
           (str "<" marsh-tag (render-attrs marsh-attrs) ">"
                content
                "</" marsh-tag ">"))))))