Fix process-bindings scope loss and async-invoke arity, bootstrap async adapter

Two bugs fixed:
1. process-bindings used merge(env) which returns {} for Env objects
   (Env is not a dict subclass). Changed to env-extend in render.sx
   and adapter-async.sx. This caused "Undefined symbol: theme" etc.
2. async-aser-eval-call passed evaled-args list to async-invoke(&rest),
   double-wrapping it. Changed to inline apply + coroutine check.

Also: bootstrap define-async into sx_ref.py (Phase 6), replace ~1000 LOC
hand-written async_eval_ref.py with 24-line thin re-export shim.

Test runner now uses Env (not flat dict) for render envs to catch scope bugs.
8 new regression tests (4 scope chain, 2 native callable arity, 2 render).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

shared/sx/ref/platform_py.py

@@ -462,10 +462,7 @@ def invoke(f, *args):
 
 def json_serialize(obj):
     import json
-    try:
-        return json.dumps(obj)
-    except (TypeError, ValueError):
-        return "{}"
+    return json.dumps(obj)
 
 
 def is_empty_dict(d):
@@ -1067,10 +1064,19 @@ import inspect
 
 from shared.sx.primitives_io import (
     IO_PRIMITIVES, RequestContext, execute_io,
-    css_class_collector as _css_class_collector_cv,
-    _svg_context as _svg_context_cv,
 )
 
+# Lazy imports to avoid circular dependency (html.py imports sx_ref.py)
+_css_class_collector_cv = None
+_svg_context_cv = None
+
+def _ensure_html_imports():
+    global _css_class_collector_cv, _svg_context_cv
+    if _css_class_collector_cv is None:
+        from shared.sx.html import css_class_collector, _svg_context
+        _css_class_collector_cv = css_class_collector
+        _svg_context_cv = _svg_context
+
 # When True, async_aser expands known components server-side
 _expand_components_cv: contextvars.ContextVar[bool] = contextvars.ContextVar(
     "_expand_components_ref", default=False
@@ -1094,18 +1100,22 @@ def expand_components_p():
 
 
 def svg_context_p():
+    _ensure_html_imports()
     return _svg_context_cv.get(False)
 
 
 def svg_context_set(val):
+    _ensure_html_imports()
     return _svg_context_cv.set(val)
 
 
 def svg_context_reset(token):
+    _ensure_html_imports()
     _svg_context_cv.reset(token)
 
 
 def css_class_collect(val):
+    _ensure_html_imports()
     collector = _css_class_collector_cv.get(None)
     if collector is not None:
         collector.update(str(val).split())
@@ -1123,6 +1133,25 @@ def is_sx_expr(x):
     return isinstance(x, SxExpr)
 
 
+# Predicate helpers used by adapter-async (these are in PRIMITIVES but
+# the bootstrapped code calls them as plain functions)
+def string_p(x):
+    return isinstance(x, str)
+
+
+def list_p(x):
+    return isinstance(x, _b_list)
+
+
+def number_p(x):
+    return isinstance(x, (int, float)) and not isinstance(x, bool)
+
+
+def sx_parse(src):
+    from shared.sx.parser import parse_all
+    return parse_all(src)
+
+
 def is_async_coroutine(x):
     return inspect.iscoroutine(x)
 
@@ -1199,48 +1228,16 @@ async def async_eval_slot_to_sx(expr, env, ctx=None):
         ctx = RequestContext()
     token = _expand_components_cv.set(True)
     try:
-        return await _eval_slot_inner(expr, env, ctx)
+        result = await async_eval_slot_inner(expr, env, ctx)
+        if isinstance(result, SxExpr):
+            return result
+        if result is None or result is NIL:
+            return SxExpr("")
+        if isinstance(result, str):
+            return SxExpr(result)
+        return SxExpr(sx_serialize(result))
     finally:
         _expand_components_cv.reset(token)
-
-
-async def _eval_slot_inner(expr, env, ctx):
-    if isinstance(expr, list) and expr:
-        head = expr[0]
-        if isinstance(head, Symbol) and head.name.startswith("~"):
-            comp = env.get(head.name)
-            if isinstance(comp, Component):
-                result = await async_aser_component(comp, expr[1:], env, ctx)
-                if isinstance(result, SxExpr):
-                    return result
-                if result is None or result is NIL:
-                    return SxExpr("")
-                if isinstance(result, str):
-                    return SxExpr(result)
-                return SxExpr(sx_serialize(result))
-    result = await async_aser(expr, env, ctx)
-    result = await _maybe_expand_component_result(result, env, ctx)
-    if isinstance(result, SxExpr):
-        return result
-    if result is None or result is NIL:
-        return SxExpr("")
-    if isinstance(result, str):
-        return SxExpr(result)
-    return SxExpr(sx_serialize(result))
-
-
-async def _maybe_expand_component_result(result, env, ctx):
-    raw = None
-    if isinstance(result, SxExpr):
-        raw = str(result).strip()
-    elif isinstance(result, str):
-        raw = result.strip()
-    if raw and raw.startswith("(~"):
-        from shared.sx.parser import parse_all as _pa
-        parsed = _pa(raw)
-        if parsed:
-            return await async_eval_slot_to_sx(parsed[0], env, ctx)
-    return result
 '''
 
 # ---------------------------------------------------------------------------
@@ -1366,7 +1363,8 @@ aser_special = _aser_special_with_continuations
 # Public API generator
 # ---------------------------------------------------------------------------
 
-def public_api_py(has_html: bool, has_sx: bool, has_deps: bool = False) -> str:
+def public_api_py(has_html: bool, has_sx: bool, has_deps: bool = False,
+                  has_async: bool = False) -> str:
     lines = [
         '',
         '# =========================================================================',
@@ -1419,8 +1417,9 @@ def public_api_py(has_html: bool, has_sx: bool, has_deps: bool = False) -> str:
 # ---------------------------------------------------------------------------
 
 ADAPTER_FILES = {
-    "html": ("adapter-html.sx", "adapter-html"),
-    "sx":   ("adapter-sx.sx",   "adapter-sx"),
+    "html":  ("adapter-html.sx",  "adapter-html"),
+    "sx":    ("adapter-sx.sx",    "adapter-sx"),
+    "async": ("adapter-async.sx", "adapter-async"),
 }
 
 SPEC_MODULES = {