Decouple core evaluator from web platform, extract libraries

The core evaluator (spec/evaluator.sx) is now the irreducible computational
core with zero web, rendering, or type-system knowledge. 2531 → 2313 lines.

- Add extensible special form registry (*custom-special-forms* + register-special-form!)
- Add render dispatch hooks (*render-check* / *render-fn*) replacing hardcoded render-active?/is-render-expr?/render-expr
- Extract freeze scopes → spec/freeze.sx (library, not core)
- Extract content addressing → spec/content.sx (library, not core)
- Move sf-deftype/sf-defeffect → spec/types.sx (self-registering)
- Move sf-defstyle → web/forms.sx (self-registering with all web forms)
- Move web tests (defpage, streaming) → web/tests/test-forms.sx
- Add is-else-clause? helper (replaces 5 inline patterns)
- Make escape-html/escape-attr library functions in render.sx (pure SX, not platform-provided)
- Add foundations plan: Step 3.5 (data representations), Step 3.7 (verified components), OCaml for Step 4d
- Update all three bootstrappers (JS 957/957, Python 744/744, OCaml 952/952)

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

spec/types.sx

@@ -4,10 +4,13 @@
 ;; Registration-time type checking: zero runtime cost.
 ;; Annotations are optional — unannotated code defaults to `any`.
 ;;
-;; Depends on: eval.sx (type-of, component accessors, env ops)
+;; This is an optional spec module — NOT part of the core evaluator.
+;; It registers deftype and defeffect via register-special-form! at load time.
+;;
+;; Depends on: evaluator.sx (type-of, component accessors, env ops)
 ;;             primitives.sx, boundary.sx (return type declarations)
 ;;
-;; Platform interface (from eval.sx, already provided):
+;; Platform interface (from evaluator.sx, already provided):
 ;;   (type-of x)            → type string
 ;;   (symbol-name s)        → string
 ;;   (keyword-name k)       → string
@@ -22,6 +25,88 @@
 ;; ==========================================================================
 
 
+;; --------------------------------------------------------------------------
+;; 0. Definition forms — deftype and defeffect
+;; --------------------------------------------------------------------------
+;; These were previously in evaluator.sx. Now they live here and register
+;; themselves via the custom special form mechanism.
+
+(define make-type-def
+  (fn ((name :as string) (params :as list) body)
+    {:name name :params params :body body}))
+
+(define normalize-type-body
+  (fn (body)
+    ;; Convert AST type expressions to type representation.
+    ;; Symbols → strings, (union ...) → (or ...), dict keys → strings.
+    (cond
+      (nil? body) "nil"
+      (= (type-of body) "symbol")
+        (symbol-name body)
+      (= (type-of body) "string")
+        body
+      (= (type-of body) "keyword")
+        (keyword-name body)
+      (= (type-of body) "dict")
+        ;; Record type — normalize values
+        (map-dict (fn (k v) (normalize-type-body v)) body)
+      (= (type-of body) "list")
+        (if (empty? body) "any"
+          (let ((head (first body)))
+            (let ((head-name (if (= (type-of head) "symbol")
+                               (symbol-name head) (str head))))
+              ;; (union a b) → (or a b)
+              (if (= head-name "union")
+                (cons "or" (map normalize-type-body (rest body)))
+                ;; (or a b), (list-of t), (-> ...) etc.
+                (cons head-name (map normalize-type-body (rest body)))))))
+      :else (str body))))
+
+(define sf-deftype
+  (fn ((args :as list) (env :as dict))
+    ;; (deftype name body) or (deftype (name a b ...) body)
+    (let ((name-or-form (first args))
+          (body-expr (nth args 1))
+          (type-name nil)
+          (type-params (list)))
+      ;; Parse name — symbol or (symbol params...)
+      (if (= (type-of name-or-form) "symbol")
+        (set! type-name (symbol-name name-or-form))
+        (when (= (type-of name-or-form) "list")
+          (set! type-name (symbol-name (first name-or-form)))
+          (set! type-params
+            (map (fn (p) (if (= (type-of p) "symbol")
+                           (symbol-name p) (str p)))
+                 (rest name-or-form)))))
+      ;; Normalize and store in *type-registry*
+      (let ((body (normalize-type-body body-expr))
+            (registry (if (env-has? env "*type-registry*")
+                        (env-get env "*type-registry*")
+                        (dict))))
+        (dict-set! registry type-name
+          (make-type-def type-name type-params body))
+        (env-bind! env "*type-registry*" registry)
+        nil))))
+
+(define sf-defeffect
+  (fn ((args :as list) (env :as dict))
+    ;; (defeffect name) — register an effect name
+    (let ((effect-name (if (= (type-of (first args)) "symbol")
+                         (symbol-name (first args))
+                         (str (first args))))
+          (registry (if (env-has? env "*effect-registry*")
+                      (env-get env "*effect-registry*")
+                      (list))))
+      (when (not (contains? registry effect-name))
+        (append! registry effect-name))
+      (env-bind! env "*effect-registry*" registry)
+      nil)))
+
+;; Register as custom special forms
+(register-special-form! "deftype" sf-deftype)
+(register-special-form! "defeffect" sf-defeffect)
+
+
 ;; --------------------------------------------------------------------------
 ;; 1. Type representation
 ;; --------------------------------------------------------------------------