OCaml CEK machine compiled to WebAssembly for browser execution

- wasm_of_ocaml compiles OCaml SX engine to WASM (722/722 spec tests)
- js_of_ocaml fallback also working (722/722 spec tests)
- Thin JS platform layer (sx-platform.js) with ~80 DOM/browser natives
- Lambda callback bridge: SX lambdas callable from JS via handle table
- Side-channel pattern bypasses js_of_ocaml return-value property stripping
- Web adapters (signals, deps, router, adapter-html) load as SX source
- Render mode dispatch: HTML tags + fragments route to OCaml renderer
- Island/component accessors handle both Component and Island types
- Dict-based signal support (signals.sx creates dicts, not native Signal)
- Scope stack implementation (collect!/collected/emit!/emitted/context)
- Bundle script embeds web adapters + WASM loader + platform layer
- SX_USE_WASM env var toggles WASM engine in dev/production
- Bootstrap extended: --web flag transpiles web adapters, :effects stripping

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

hosts/ocaml/browser/build.sh

@@ -0,0 +1,37 @@
+#!/usr/bin/env bash
+# Build the OCaml SX engine for browser use (WASM + JS fallback).
+#
+# Outputs:
+#   _build/default/browser/sx_browser.bc.wasm.js       WASM loader
+#   _build/default/browser/sx_browser.bc.wasm.assets/   WASM modules
+#   _build/default/browser/sx_browser.bc.js             JS fallback
+#
+# Usage:
+#   cd hosts/ocaml && ./browser/build.sh
+
+set -euo pipefail
+cd "$(dirname "$0")/.."
+
+eval $(opam env 2>/dev/null || true)
+
+echo "=== Building OCaml SX browser engine ==="
+
+# Build all targets: bytecode, JS, WASM
+dune build browser/sx_browser.bc.js browser/sx_browser.bc.wasm.js
+
+echo ""
+echo "--- Output sizes ---"
+echo -n "JS (unoptimized):  "; ls -lh _build/default/browser/sx_browser.bc.js | awk '{print $5}'
+echo -n "WASM loader:       "; ls -lh _build/default/browser/sx_browser.bc.wasm.js | awk '{print $5}'
+echo -n "WASM modules:      "; du -sh _build/default/browser/sx_browser.bc.wasm.assets/*.wasm | awk '{s+=$1}END{print s"K"}'
+
+# Optimized JS build
+js_of_ocaml --opt=3 -o _build/default/browser/sx_browser.opt.js _build/default/browser/sx_browser.bc
+echo -n "JS (optimized):    "; ls -lh _build/default/browser/sx_browser.opt.js | awk '{print $5}'
+
+echo ""
+echo "=== Build complete ==="
+echo ""
+echo "Test with:"
+echo "  node hosts/ocaml/browser/run_tests_js.js                                    # JS"
+echo "  node --experimental-wasm-imported-strings hosts/ocaml/browser/run_tests_wasm.js  # WASM"