Fix aser list flattening bug, add wire format test suite (41 tests)

The sync aser-call in adapter-sx.sx didn't flatten list results from
map/filter in positional children — serialize(list) wrapped in parens
creating ((div ...) ...) which re-parses as an invalid call. Rewrote
aser-call from reduce to for-each (bootstrapper can't nest for-each
inside reduce lambdas) and added list flattening in both aser-call
and aser-fragment.

Also adds test-aser.sx (41 tests), render-sx platform function,
expanded test-render.sx (+7 map/filter children tests), and specs
async-eval-slot-inner in adapter-async.sx.

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

shared/sx/tests/run.py

@@ -134,6 +134,28 @@ def render_html(sx_source):
     return result
 
 
+# --- Render SX (aser) platform function ---
+
+def render_sx(sx_source):
+    """Parse SX source and serialize to SX wire format via the bootstrapped evaluator."""
+    try:
+        from shared.sx.ref.sx_ref import aser as _aser, serialize as _serialize
+    except ImportError:
+        raise RuntimeError("aser not available — sx_ref.py not built")
+    exprs = parse_all(sx_source)
+    render_env = dict(env)
+    result = ""
+    for expr in exprs:
+        val = _aser(expr, render_env)
+        if isinstance(val, str):
+            result += val
+        elif val is None or val is NIL:
+            pass
+        else:
+            result += _serialize(val)
+    return result
+
+
 # --- Signal platform primitives ---
 # Implements the signal runtime platform interface for testing signals.sx
 
@@ -258,6 +280,7 @@ SPECS = {
     "parser":        {"file": "test-parser.sx",        "needs": ["sx-parse"]},
     "router":        {"file": "test-router.sx",        "needs": []},
     "render":        {"file": "test-render.sx",        "needs": ["render-html"]},
+    "aser":          {"file": "test-aser.sx",          "needs": ["render-sx"]},
     "deps":          {"file": "test-deps.sx",          "needs": []},
     "engine":        {"file": "test-engine.sx",        "needs": []},
     "orchestration": {"file": "test-orchestration.sx", "needs": []},
@@ -296,8 +319,9 @@ env = _Env({
     "make-keyword": make_keyword,
     "symbol-name": symbol_name,
     "keyword-name": keyword_name,
-    # Render platform function
+    # Render platform functions
     "render-html": render_html,
+    "render-sx": render_sx,
     # Extra primitives needed by spec modules (router.sx, deps.sx)
     "for-each-indexed": "_deferred",  # replaced below
     "dict-set!": "_deferred",
@@ -773,9 +797,9 @@ def main():
             print(f"# --- {spec_name} ---")
             eval_file(spec["file"], env)
 
-            # Reset render state after render tests to avoid leaking
+            # Reset render state after render/aser tests to avoid leaking
             # into subsequent specs (bootstrapped evaluator checks render_active)
-            if spec_name == "render":
+            if spec_name in ("render", "aser"):
                 try:
                     from shared.sx.ref.sx_ref import set_render_active_b
                     set_render_active_b(False)