Fix filter/map tag disambiguation inside SVG context without keyword attrs

(filter (feTurbulence ...)) inside (svg ...) has no keyword first arg,
so the keyword-only check dispatched it as a HO function. Now also
check SVG/MathML context (ns in client, _svg_context in server).

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

shared/sx/async_eval.py

@@ -648,10 +648,13 @@ async def _arender_list(expr: list, env: dict[str, Any], ctx: RequestContext) ->
             return await _arender_element(name[5:], expr[1:], env, ctx)
 
         # Render-aware special forms
-        # If name is also an HTML tag and first arg is Keyword → tag call
+        # If name is also an HTML tag and (keyword arg or SVG context) → tag call
         arsf = _ASYNC_RENDER_FORMS.get(name)
         if arsf is not None:
-            if name in HTML_TAGS and len(expr) > 1 and isinstance(expr[1], Keyword):
+            if name in HTML_TAGS and (
+                (len(expr) > 1 and isinstance(expr[1], Keyword))
+                or _svg_context.get(False)
+            ):
                 return await _arender_element(name, expr[1:], env, ctx)
             return await arsf(expr, env, ctx)
 
@@ -1098,10 +1101,13 @@ async def _aser(expr: Any, env: dict[str, Any], ctx: RequestContext) -> Any:
 
         # Serialize-mode special/HO forms (checked BEFORE HTML_TAGS
         # because some names like "map" are both HTML tags and sx forms).
-        # If name is also an HTML tag and first arg is Keyword → tag call.
+        # If name is also an HTML tag and (keyword arg or SVG context) → tag call.
         sf = _ASER_FORMS.get(name)
         if sf is not None:
-            if name in HTML_TAGS and len(expr) > 1 and isinstance(expr[1], Keyword):
+            if name in HTML_TAGS and (
+                (len(expr) > 1 and isinstance(expr[1], Keyword))
+                or _svg_context.get(False)
+            ):
                 return await _aser_call(name, expr[1:], env, ctx)
             return await sf(expr, env, ctx)