OCaml evaluator for page dispatch + handler aser, 83/83 Playwright tests

Major architectural change: page function dispatch and handler execution
now go through the OCaml kernel instead of the Python bootstrapped evaluator.

OCaml integration:
- Page dispatch: bridge.eval() evaluates SX URL expressions (geography, marshes, etc.)
- Handler aser: bridge.aser() serializes handler responses as SX wire format
- _ensure_components loads all .sx files into OCaml kernel (spec, web adapter, handlers)
- defhandler/defpage registered as no-op special forms so handler files load
- helper IO primitive dispatches to Python page helpers + IO handlers
- ok-raw response format for SX wire format (no double-escaping)
- Natural list serialization in eval (no (list ...) wrapper)
- Clean pipe: _read_until_ok always sends io-response on error

SX adapter (aser):
- scope-emit!/scope-peek aliases to avoid CEK special form conflict
- aser-fragment/aser-call: strings starting with "(" pass through unserialized
- Registered cond-scheme?, is-else-clause?, primitive?, get-primitive in kernel
- random-int, parse-int as kernel primitives; json-encode, into via IO bridge

Handler migration:
- All IO calls converted to (helper "name" args...) pattern
- request-arg, request-form, state-get, state-set!, now, component-source etc.
- Fixed bare (effect ...) in island bodies leaking disposer functions as text
- Fixed lower-case → lower, ~search-results → ~examples/search-results

Reactive islands:
- sx-hydrate-islands called after client-side navigation swap
- force-dispose-islands-in for outerHTML swaps (clears hydration markers)
- clear-processed! platform primitive for re-hydration

Content restructuring:
- Design, event bridge, named stores, phase 2 consolidated into reactive overview
- Marshes split into overview + 5 example sub-pages
- Nav links use sx-get/sx-target for client-side navigation

Playwright test suite (sx/tests/test_demos.py):
- 83 tests covering hypermedia demos, reactive islands, marshes, spec explorer
- Server-side rendering, handler interactions, island hydration, navigation

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

shared/sx/primitives_io.py

@@ -642,7 +642,8 @@ from . import primitives_ctx  # noqa: E402, F401
 # Auto-derive IO_PRIMITIVES from registered handlers
 # ---------------------------------------------------------------------------
 
-IO_PRIMITIVES: frozenset[str] = frozenset(_IO_HANDLERS.keys())
+# Placeholder — rebuilt at end of file after all handlers are registered
+IO_PRIMITIVES: frozenset[str] = frozenset()
 
 
 # ---------------------------------------------------------------------------
@@ -703,9 +704,45 @@ _PRIMITIVES["relations-from"] = _bridge_relations_from
 # Validate all IO handlers against boundary.sx
 # ---------------------------------------------------------------------------
 
+@register_io_handler("helper")
+async def _io_helper(
+    args: list[Any], kwargs: dict[str, Any], ctx: RequestContext
+) -> Any:
+    """``(helper "name" args...)`` → dispatch to page helpers or IO handlers.
+
+    Universal IO dispatcher — same interface as the OCaml kernel's helper
+    IO primitive. Checks page helpers first, then IO handlers.
+    """
+    if not args:
+        raise ValueError("helper requires a name")
+    name = str(args[0])
+    helper_args = args[1:]
+
+    # Check page helpers first
+    from .pages import get_page_helpers
+    helpers = get_page_helpers("sx")
+    fn = helpers.get(name)
+    if fn is not None:
+        import asyncio
+        result = fn(*helper_args)
+        if asyncio.iscoroutine(result):
+            result = await result
+        return result
+
+    # Fall back to IO handlers
+    io_handler = _IO_HANDLERS.get(name)
+    if io_handler is not None:
+        return await io_handler(helper_args, {}, ctx)
+
+    raise ValueError(f"Unknown helper: {name!r}")
+
+
 def _validate_io_handlers() -> None:
     from .boundary import validate_io
     for name in _IO_HANDLERS:
         validate_io(name)
 
 _validate_io_handlers()
+
+# Rebuild IO_PRIMITIVES now that all handlers (including helper) are registered
+IO_PRIMITIVES = frozenset(_IO_HANDLERS.keys())