Add sibling sublist parser tests + reset JIT sx-parse

Tests: parse "(a (b) (c))" must produce 3 siblings, not nested.
Catches JIT compilation bug where closing parens cause sibling
lists to become children.

Reset sx-parse to CEK on the OCaml kernel — the JIT-compiled
version of sx-parse's complex letrec produces wrong bytecode.
CEK interpretation works correctly (tests pass on all platforms).

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

shared/sx/ocaml_bridge.py

@@ -440,6 +440,16 @@ class OcamlBridge:
                         _logger.warning("OCaml load skipped %s: %s",
                                         filepath, e)
 
+                # JIT workaround: sx-parse has a complex letrec (20 mutually
+                # recursive functions) that the JIT compiles incorrectly —
+                # closing parens cause siblings to become children.
+                # CEK-interpreted sx-parse works correctly.
+                try:
+                    await self._send('(vm-reset-fn "sx-parse")')
+                    await self._read_until_ok(ctx=None)
+                except OcamlBridgeError:
+                    pass
+
                 # SSR overrides: effect is a no-op on the server (prevents
                 # reactive loops during island SSR — effects are DOM side-effects)
                 try: