Complete Python eval removal: epoch protocol, scope consolidation, JIT fixes

Route all rendering through OCaml bridge — render_to_html no longer uses
Python async_eval. Fix register_components to parse &key params and &rest
children from defcomp forms. Remove all dead sx_ref.py imports.

Epoch protocol (prevents pipe desync):
- Every command prefixed with (epoch N), all responses tagged with epoch
- Both sides discard stale-epoch messages — desync structurally impossible
- OCaml main loop discards stale io-responses between commands

Consolidate scope primitives into sx_scope.ml:
- Single source of truth for scope-push!/pop!/peek, collect!/collected,
  emit!/emitted, context, and 12 other scope operations
- Removes duplicate registrations from sx_server.ml (including bugs where
  scope-emit! and clear-collected! were registered twice with different impls)
- Bind scope prims into env so JIT VM finds them via OP_GLOBAL_GET

JIT VM fixes:
- Trampoline thunks before passing args to CALL_PRIM
- as_list resolves thunks via _sx_trampoline_fn
- len handles all value types (Bool, Number, RawHTML, SxExpr, Spread, etc.)

Other fixes:
- ~cssx/tw signature: (tokens) → (&key tokens) to match callers
- Minimal Python evaluator in html.py for sync sx() Jinja function
- Python scope primitive stubs (thread-local) for non-OCaml paths
- Reader macro resolution via OcamlSync instead of sx_ref.py

Tests: 1114 OCaml, 1078 JS, 35 Python regression, 6/6 Playwright SSR

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

shared/sx/primitives.py

@@ -579,26 +579,54 @@ def prim_json_encode(value) -> str:
 # (shared global state between transpiled and hand-written evaluators)
 # ---------------------------------------------------------------------------
 
-def _lazy_scope_primitives():
-    """Register scope/provide/collect primitives from sx_ref.py.
+def _register_scope_primitives():
+    """Register scope/provide/collect primitive stubs.
 
-    Called at import time — if sx_ref.py isn't built yet, silently skip.
-    These are needed by the hand-written _aser in async_eval.py when
-    expanding components that use scoped effects (e.g. ~cssx/flush).
+    The OCaml kernel provides the real implementations. These stubs exist
+    so _PRIMITIVES contains the names for dependency analysis, and so
+    any Python-side code that checks for their existence finds them.
     """
-    try:
-        from .ref.sx_ref import (
-            sx_collect, sx_collected, sx_clear_collected,
-            sx_emitted, sx_emit, sx_context,
-        )
-        _PRIMITIVES["collect!"] = sx_collect
-        _PRIMITIVES["collected"] = sx_collected
-        _PRIMITIVES["clear-collected!"] = sx_clear_collected
-        _PRIMITIVES["emitted"] = sx_emitted
-        _PRIMITIVES["emit!"] = sx_emit
-        _PRIMITIVES["context"] = sx_context
-    except ImportError:
-        pass
+    import threading
+    _scope_data = threading.local()
 
-_lazy_scope_primitives()
+    def _collect(channel, value):
+        if not hasattr(_scope_data, 'collected'):
+            _scope_data.collected = {}
+        _scope_data.collected.setdefault(channel, []).append(value)
+        return NIL
+
+    def _collected(channel):
+        if not hasattr(_scope_data, 'collected'):
+            return []
+        return list(_scope_data.collected.get(channel, []))
+
+    def _clear_collected(channel):
+        if hasattr(_scope_data, 'collected'):
+            _scope_data.collected.pop(channel, None)
+        return NIL
+
+    def _emit(channel, value):
+        if not hasattr(_scope_data, 'emitted'):
+            _scope_data.emitted = {}
+        _scope_data.emitted.setdefault(channel, []).append(value)
+        return NIL
+
+    def _emitted(channel):
+        if not hasattr(_scope_data, 'emitted'):
+            return []
+        return list(_scope_data.emitted.get(channel, []))
+
+    def _context(key):
+        if not hasattr(_scope_data, 'context'):
+            return NIL
+        return _scope_data.context.get(key, NIL) if isinstance(_scope_data.context, dict) else NIL
+
+    _PRIMITIVES["collect!"] = _collect
+    _PRIMITIVES["collected"] = _collected
+    _PRIMITIVES["clear-collected!"] = _clear_collected
+    _PRIMITIVES["emitted"] = _emitted
+    _PRIMITIVES["emit!"] = _emit
+    _PRIMITIVES["context"] = _context
+
+_register_scope_primitives()