Replace invoke with cek-call in reactive island primitives

All signal operations (computed, effect, batch, etc.) now dispatch
function calls through cek-call, which routes SX lambdas via cek-run
and native callables via apply. This replaces the invoke shim.

Key changes:
- cek.sx: add cek-call (defined before reactive-shift-deref), replace
  invoke in subscriber disposal and ReactiveResetFrame handler
- signals.sx: replace all 11 invoke calls with cek-call
- js.sx: fix octal escape in js-quote-string (char-from-code 0)
- platform_js.py: fix JS append to match Python (list concat semantics),
  add Continuation type guard in PLATFORM_CEK_JS, add scheduleIdle
  safety check, module ordering (cek before signals)
- platform_py.py: fix ident-char regex (remove [ ] from valid chars),
  module ordering (cek before signals)
- run_js_sx.py: emit PLATFORM_CEK_JS before transpiled spec files
- page-functions.sx: add cek and provide page functions for SX URLs

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

shared/sx/ref/boundary_parser.py

@@ -20,17 +20,21 @@ logger = logging.getLogger("sx.boundary_parser")
 
 # Allow standalone use (from bootstrappers) or in-project imports
 try:
-    from shared.sx.parser import parse_all
     from shared.sx.types import Symbol, Keyword, NIL as SX_NIL
 except ImportError:
     import sys
     _HERE = os.path.dirname(os.path.abspath(__file__))
     _PROJECT = os.path.abspath(os.path.join(_HERE, "..", "..", ".."))
     sys.path.insert(0, _PROJECT)
-    from shared.sx.parser import parse_all
     from shared.sx.types import Symbol, Keyword, NIL as SX_NIL
 
 
+def _get_parse_all():
+    """Lazy import to avoid circular dependency when parser.py loads sx_ref.py."""
+    from shared.sx.parser import parse_all
+    return parse_all
+
+
 def _ref_dir() -> str:
     return os.path.dirname(os.path.abspath(__file__))
 
@@ -81,7 +85,7 @@ def _extract_declarations(
 
     Returns (io_names, {service: helper_names}).
     """
-    exprs = parse_all(source)
+    exprs = _get_parse_all()(source)
     io_names: set[str] = set()
     helpers: dict[str, set[str]] = {}
 
@@ -144,7 +148,7 @@ def parse_primitives_sx() -> frozenset[str]:
 def parse_primitives_by_module() -> dict[str, frozenset[str]]:
     """Parse primitives.sx and return primitives grouped by module."""
     source = _read_file("primitives.sx")
-    exprs = parse_all(source)
+    exprs = _get_parse_all()(source)
     modules: dict[str, set[str]] = {}
     current_module = "_unscoped"
 
@@ -204,7 +208,7 @@ def parse_primitive_param_types() -> dict[str, dict]:
     type of the &rest parameter (or None if no &rest, or None if untyped &rest).
     """
     source = _read_file("primitives.sx")
-    exprs = parse_all(source)
+    exprs = _get_parse_all()(source)
     result: dict[str, dict] = {}
 
     for expr in exprs:
@@ -293,7 +297,7 @@ def parse_boundary_effects() -> dict[str, list[str]]:
     Pure primitives from primitives.sx are not included (they have no effects).
     """
     source = _read_file("boundary.sx")
-    exprs = parse_all(source)
+    exprs = _get_parse_all()(source)
     result: dict[str, list[str]] = {}
 
     _DECL_FORMS = {
@@ -338,7 +342,7 @@ def parse_boundary_effects() -> dict[str, list[str]]:
 def parse_boundary_types() -> frozenset[str]:
     """Parse boundary.sx and return the declared boundary type names."""
     source = _read_file("boundary.sx")
-    exprs = parse_all(source)
+    exprs = _get_parse_all()(source)
     for expr in exprs:
         if (isinstance(expr, list) and len(expr) >= 2
                 and isinstance(expr[0], Symbol)