Fix _aser_call and sx_call list serialization: use (list ...) for data arrays

Data lists (dicts, strings, numbers) were wrapped in (<> ...) fragments
which the client rendered as empty DocumentFragments instead of iterable
arrays. This broke map/filter over cards, tag_groups, and authors in
blog index and similar components.

- _aser_call: data lists → (list ...), rendered content (SxExpr) → (<> ...)
- sx_call: all list kwargs → (list ...)

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

shared/sx/async_eval.py

@@ -1253,15 +1253,25 @@ async def _aser_call(
                         extra_class = val.class_name
                     else:
                         parts.append(f":{arg.name}")
-                        # Plain list (e.g. from map) → wrap as fragment to
+                        # Plain list → serialize for the client.
-                        # avoid ambiguity with function application on re-parse
+                        # Rendered items (SxExpr) → wrap in (<> ...) fragment.
+                        # Data items (dicts, strings, numbers) → (list ...)
+                        # so the client gets an iterable array, not a
+                        # DocumentFragment that breaks map/filter.
                         if isinstance(val, list):
-                            items = [serialize(v) for v in val
+                            live = [v for v in val
-                                     if v is not NIL and v is not None]
+                                    if v is not NIL and v is not None]
-                            parts.append(
+                            items = [serialize(v) for v in live]
-                                "(<> " + " ".join(items) + ")" if items
+                            if not items:
-                                else "nil"
+                                parts.append("nil")
-                            )
+                            elif any(isinstance(v, SxExpr) for v in live):
+                                parts.append(
+                                    "(<> " + " ".join(items) + ")"
+                                )
+                            else:
+                                parts.append(
+                                    "(list " + " ".join(items) + ")"
+                                )
                         else:
                             parts.append(serialize(val))
                 i += 2

shared/sx/helpers.py

@@ -404,13 +404,22 @@ def sx_call(component_name: str, **kwargs: Any) -> str:
 
     Values are serialized: strings are quoted, None becomes nil,
     bools become true/false, numbers stay as-is.
+    List values use ``(list ...)`` so the client gets an iterable array
+    rather than a rendered fragment.
     """
-    from .parser import serialize
+    from .parser import serialize, SxExpr
     name = component_name if component_name.startswith("~") else f"~{component_name}"
     parts = [name]
     for key, val in kwargs.items():
         parts.append(f":{key.replace('_', '-')}")
-        parts.append(serialize(val))
+        if isinstance(val, list):
+            items = [serialize(v) for v in val if v is not None]
+            if not items:
+                parts.append("nil")
+            else:
+                parts.append("(list " + " ".join(items) + ")")
+        else:
+            parts.append(serialize(val))
     return "(" + " ".join(parts) + ")"