Bootstrap CEK as default evaluator on both JS and Python sides

SPEC_MODULES + SPEC_MODULE_ORDER for frames/cek in platform_js.py,
PLATFORM_CEK_JS + CEK_FIXUPS_JS constants, auto-inclusion in
run_js_sx.py, 70+ RENAMES in js.sx. Python: CEK always-include in
bootstrap_py.py, eval_expr/trampoline overridden to cek_run in
platform_py.py with _tree_walk_* preserved for test runners.

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

shared/sx/ref/platform_py.py

@@ -659,51 +659,6 @@ def escape_string(s):
         .replace("</script", "<\\\\/script"))
 
 
-def serialize(val):
-    """Serialize an SX value to SX source text.
-
-    Note: parser.sx defines sx-serialize with a serialize alias, but parser.sx
-    is only included in JS builds (for client-side parsing). Python builds
-    provide this as a platform function.
-    """
-    t = type_of(val)
-    if t == "sx-expr":
-        return val.source
-    if t == "nil":
-        return "nil"
-    if t == "boolean":
-        return "true" if val else "false"
-    if t == "number":
-        return str(val)
-    if t == "string":
-        return '"' + escape_string(val) + '"'
-    if t == "symbol":
-        return symbol_name(val)
-    if t == "keyword":
-        return ":" + keyword_name(val)
-    if t == "raw-html":
-        escaped = escape_string(raw_html_content(val))
-        return '(raw! "' + escaped + '")'
-    if t == "list":
-        if not val:
-            return "()"
-        items = [serialize(x) for x in val]
-        return "(" + " ".join(items) + ")"
-    if t == "dict":
-        items = []
-        for k, v in val.items():
-            items.append(":" + str(k))
-            items.append(serialize(v))
-        return "{" + " ".join(items) + "}"
-    if callable(val):
-        return "nil"
-    return str(val)
-
-# Aliases for transpiled code — parser.sx defines sx-serialize/sx-serialize-dict
-# but parser.sx is JS-only. Provide aliases so transpiled render.sx works.
-sx_serialize = serialize
-sx_serialize_dict = lambda d: serialize(d)
-
 _SPECIAL_FORM_NAMES = frozenset()  # Placeholder — overridden by transpiled adapter-sx.sx
 _HO_FORM_NAMES = frozenset()
 
@@ -1066,6 +1021,55 @@ has_key_p = PRIMITIVES["has-key?"]
 dict_p = PRIMITIVES["dict?"]
 dissoc = PRIMITIVES["dissoc"]
 index_of = PRIMITIVES["index-of"]
+lower = PRIMITIVES["lower"]
+char_from_code = PRIMITIVES["char-from-code"]
+'''
+
+# ---------------------------------------------------------------------------
+# Platform: parser module — character classification, number parsing,
+# reader macro registry
+# ---------------------------------------------------------------------------
+
+PLATFORM_PARSER_PY = '''
+# =========================================================================
+# Platform interface — Parser
+# =========================================================================
+
+import re as _re_parser
+
+_IDENT_START_RE = _re_parser.compile(r"[a-zA-Z_~*+\\-><=/!?&]")
+_IDENT_CHAR_RE = _re_parser.compile(r"[a-zA-Z0-9_~*+\\-><=/!?.:&/\\[\\]#,]")
+
+
+def ident_start_p(ch):
+    return bool(_IDENT_START_RE.match(ch))
+
+
+def ident_char_p(ch):
+    return bool(_IDENT_CHAR_RE.match(ch))
+
+
+def parse_number(s):
+    """Parse a numeric string to int or float."""
+    try:
+        if "." in s or "e" in s or "E" in s:
+            return float(s)
+        return int(s)
+    except (ValueError, TypeError):
+        return float(s)
+
+
+# Reader macro registry
+_reader_macros = {}
+
+
+def reader_macro_get(name):
+    return _reader_macros.get(name, NIL)
+
+
+def reader_macro_set_b(name, handler):
+    _reader_macros[name] = handler
+    return NIL
 '''
 
 # ---------------------------------------------------------------------------
@@ -1159,6 +1163,23 @@ def cek_run(state):
     while not cek_terminal_p(state):
         state = cek_step(state)
     return cek_value(state)
+
+# CEK is the canonical evaluator — override eval_expr to use it.
+# The tree-walk evaluator (eval_expr from eval.sx) is superseded.
+_tree_walk_eval_expr = eval_expr
+
+def eval_expr(expr, env):
+    """Evaluate expr using the CEK machine."""
+    return cek_run(make_cek_state(expr, env, []))
+
+# CEK never produces thunks — trampoline becomes identity
+_tree_walk_trampoline = trampoline
+
+def trampoline(val):
+    """In CEK mode, values are immediate — resolve any legacy thunks."""
+    if is_thunk(val):
+        return eval_expr(thunk_expr(val), thunk_env(val))
+    return val
 '''
 
 # ---------------------------------------------------------------------------
@@ -1258,11 +1279,6 @@ 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)
 
@@ -1590,9 +1606,10 @@ def public_api_py(has_html: bool, has_sx: bool, has_deps: bool = False,
 # ---------------------------------------------------------------------------
 
 ADAPTER_FILES = {
-    "html":  ("adapter-html.sx",  "adapter-html"),
-    "sx":    ("adapter-sx.sx",    "adapter-sx"),
-    "async": ("adapter-async.sx", "adapter-async"),
+    "parser": ("parser.sx",       "parser"),
+    "html":   ("adapter-html.sx", "adapter-html"),
+    "sx":     ("adapter-sx.sx",   "adapter-sx"),
+    "async":  ("adapter-async.sx", "adapter-async"),
 }
 
 SPEC_MODULES = {