WASM browser build: interned env keys, async kernel boot, bundled .sx platform

- Symbol interning in sx_types.ml: env lookups use int keys (intern/unintern)
  to avoid repeated string hashing in scope chain walks
- sx-platform.js: poll for SxKernel availability (WASM init is async)
- shell.sx: load sx_browser.bc.wasm.js when SX_USE_WASM=1
- bundle.sh: fix .sx file paths (web-signals.sx rename)
- browser/dune: target byte+js+wasm modes
- Bundle 23 .sx platform files for browser (dom, signals, router, boot, etc.)

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

shared/static/wasm/sx/freeze.sx

@@ -0,0 +1,94 @@
+;; ==========================================================================
+;; freeze.sx — Serializable state boundaries
+;;
+;; Freeze scopes collect signals registered within them. On freeze,
+;; their current values are serialized to SX. On thaw, values are
+;; restored. Multiple named scopes can coexist independently.
+;;
+;; This is a library built on top of the evaluator's scoped effects
+;; (scope-push!/scope-pop!/context) and signal system. It is NOT
+;; part of the core evaluator — it loads after evaluator.sx.
+;;
+;; Usage:
+;;   (freeze-scope "editor"
+;;     (let ((doc (signal "hello")))
+;;       (freeze-signal "doc" doc)
+;;       ...))
+;;
+;;   (cek-freeze-scope "editor")  → {:name "editor" :signals {:doc "hello"}}
+;;   (cek-thaw-scope "editor" frozen-data)  → restores signal values
+;; ==========================================================================
+
+;; Registry of freeze scopes: name → list of {name signal} entries
+(define freeze-registry (dict))
+
+;; Register a signal in the current freeze scope
+(define freeze-signal :effects [mutation]
+  (fn (name sig)
+    (let ((scope-name (context "sx-freeze-scope" nil)))
+      (when scope-name
+        (let ((entries (or (get freeze-registry scope-name) (list))))
+          (append! entries (dict "name" name "signal" sig))
+          (dict-set! freeze-registry scope-name entries))))))
+
+;; Freeze scope delimiter — collects signals registered within body
+(define freeze-scope :effects [mutation]
+  (fn (name body-fn)
+    (scope-push! "sx-freeze-scope" name)
+    ;; Initialize empty entry list for this scope
+    (dict-set! freeze-registry name (list))
+    (cek-call body-fn nil)
+    (scope-pop! "sx-freeze-scope")
+    nil))
+
+;; Freeze a named scope → SX dict of signal values
+(define cek-freeze-scope :effects []
+  (fn (name)
+    (let ((entries (or (get freeze-registry name) (list)))
+          (signals-dict (dict)))
+      (for-each (fn (entry)
+        (dict-set! signals-dict
+          (get entry "name")
+          (signal-value (get entry "signal"))))
+        entries)
+      (dict "name" name "signals" signals-dict))))
+
+;; Freeze all scopes
+(define cek-freeze-all :effects []
+  (fn ()
+    (map (fn (name) (cek-freeze-scope name))
+      (keys freeze-registry))))
+
+;; Thaw a named scope — restore signal values from frozen data
+(define cek-thaw-scope :effects [mutation]
+  (fn (name frozen)
+    (let ((entries (or (get freeze-registry name) (list)))
+          (values (get frozen "signals")))
+      (when values
+        (for-each (fn (entry)
+          (let ((sig-name (get entry "name"))
+                (sig (get entry "signal"))
+                (val (get values sig-name)))
+            (when (not (nil? val))
+              (reset! sig val))))
+          entries)))))
+
+;; Thaw all scopes from a list of frozen scope dicts
+(define cek-thaw-all :effects [mutation]
+  (fn (frozen-list)
+    (for-each (fn (frozen)
+      (cek-thaw-scope (get frozen "name") frozen))
+      frozen-list)))
+
+;; Serialize a frozen scope to SX text
+(define freeze-to-sx :effects []
+  (fn (name)
+    (sx-serialize (cek-freeze-scope name))))
+
+;; Restore from SX text
+(define thaw-from-sx :effects [mutation]
+  (fn (sx-text)
+    (let ((parsed (sx-parse sx-text)))
+      (when (not (empty? parsed))
+        (let ((frozen (first parsed)))
+          (cek-thaw-scope (get frozen "name") frozen))))))