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>

sx/sx/provide.sx

@@ -67,10 +67,12 @@
   (~docs/page :title "Provide / Context / Emit!"
 
     (p :class "text-stone-500 text-sm italic mb-8"
-      "Render-time dynamic scope. " (code "provide") " creates a named scope with a value "
-      "and an accumulator. " (code "context") " reads the value downward. "
+      "Sugar for " (code "scope") " with a value. " (code "provide") " creates a named scope "
+      "with a value and an accumulator. " (code "context") " reads the value downward. "
       (code "emit!") " appends to the accumulator upward. " (code "emitted") " retrieves what was emitted. "
-      "This is the substrate that spreads, CSSX, and script collection are built on.")
+      "See "
+      (a :href "/sx/(geography.(scopes))" :class "text-violet-600 hover:underline" "scopes")
+      " for the unified primitive.")
 
     ;; =====================================================================
     ;; I. The four primitives
@@ -215,25 +217,26 @@
     ;; =====================================================================
 
     (~docs/section :title "Platform implementation" :id "platform"
-      (p "Each platform (Python, JavaScript) must provide five operations. "
-         "The platform manages per-name stacks — each stack entry has a value and an "
-         "emitted list.")
+      (p (code "provide") " is sugar for " (code "scope") ". At the platform level, "
+         (code "provide-push!") " and " (code "provide-pop!") " are aliases for "
+         (code "scope-push!") " and " (code "scope-pop!") ". All operations work on a unified "
+         (code "_scope_stacks") " data structure.")
 
       (~docs/table
         :headers (list "Platform primitive" "Purpose")
         :rows (list
-          (list "provide-push!(name, value)" "Push a new scope with value and empty emitted list")
-          (list "provide-pop!(name)" "Pop the most recent scope")
+          (list "scope-push!(name, value)" "Push a new scope with value and empty accumulator")
+          (list "scope-pop!(name)" "Pop the most recent scope")
           (list "context(name, ...default)" "Read value from nearest scope (error if missing and no default)")
-          (list "emit!(name, value)" "Append to nearest scope's emitted list (tolerant: no-op if missing)")
-          (list "emitted(name)" "Return list of emitted values from nearest scope")))
+          (list "emit!(name, value)" "Append to nearest scope's accumulator (tolerant: no-op if missing)")
+          (list "emitted(name)" "Return accumulated values from nearest scope")))
 
-      (p (code "provide") " itself is a special form in "
+      (p (code "provide") " is a special form in "
          (a :href "/sx/(language.(spec.(explore.evaluator)))" :class "font-mono text-violet-600 hover:underline text-sm" "eval.sx")
-         " — it calls " (code "provide-push!") ", evaluates the body, "
-         "then calls " (code "provide-pop!") ". The five platform primitives are declared in "
-         (a :href "/sx/(language.(spec.(explore.boundary)))" :class "font-mono text-violet-600 hover:underline text-sm" "boundary.sx")
-         " (Tier 5: Dynamic scope).")
+         " — it calls " (code "scope-push!") ", evaluates the body, "
+         "then calls " (code "scope-pop!") ". See "
+         (a :href "/sx/(geography.(scopes))" :class "text-violet-600 hover:underline" "scopes")
+         " for the full unified platform.")
 
       (~docs/note
         (p (strong "Spec explorer: ") "See the provide/emit! primitives in "