Fix examples.sx: paren balance + dict eval crash at startup

1. Extra closing paren in ex-tabs handler
2. tab-content dict values contained (div ...) HTML tags which crash
   during register_components since HTML primitives aren't in env

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

sx/sxc/pages/helpers.py

@@ -35,6 +35,7 @@ def _register_sx_helpers() -> None:
         "prove-data": _prove_data,
         "page-helpers-demo-data": _page_helpers_demo_data,
         "spec-explorer-data": _spec_explorer_data,
+        "handler-source": _handler_source,
     })
 
 
@@ -68,6 +69,35 @@ def _component_source(name: str) -> str:
     })
 
 
+def _handler_source(name: str) -> str:
+    """Return the pretty-printed defhandler source for a named handler."""
+    from shared.sx.handlers import get_handler
+    from shared.sx.parser import serialize
+
+    hdef = get_handler("sx", name)
+    if not hdef:
+        return f";;; Handler not found: {name}"
+
+    parts = [f"(defhandler {hdef.name}"]
+    if hdef.path:
+        parts.append(f'  :path "{hdef.path}"')
+    if hdef.method != "get":
+        parts.append(f"  :method :{hdef.method}")
+    if not hdef.csrf:
+        parts.append("  :csrf false")
+    if hdef.returns != "element":
+        parts.append(f'  :returns "{hdef.returns}"')
+    param_strs = ["&key"] + list(hdef.params) if hdef.params else []
+    parts.append(f"  ({' '.join(param_strs)})" if param_strs else "  ()")
+    body_sx = serialize(hdef.body, pretty=True)
+    # Indent body by 2 spaces
+    body_lines = body_sx.split("\n")
+    parts.append("  " + body_lines[0])
+    for line in body_lines[1:]:
+        parts.append("  " + line)
+    return "\n".join(parts) + ")"
+
+
 def _primitives_data() -> dict:
     """Return the PRIMITIVES dict for the primitives docs page."""
     from content.pages import PRIMITIVES