OCaml bootstrapper Phase 2: HTML renderer, SX server, Python bridge

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

sx/app.py

@@ -148,6 +148,21 @@ def create_app() -> "Quart":
             target = path + "/" + ("?" + qs if qs else "")
             return redirect(target, 301)
 
+    @app.get("/sx/_engine")
+    async def sx_engine_info():
+        """Diagnostic: which SX engine is active."""
+        import os, json
+        info = {"engine": "python-ref", "ocaml": False}
+        if os.environ.get("SX_USE_OCAML") == "1":
+            try:
+                from shared.sx.ocaml_bridge import get_bridge
+                bridge = await get_bridge()
+                engine = await bridge.ping()
+                info = {"engine": engine, "ocaml": True, "pid": bridge._proc.pid}
+            except Exception as e:
+                info = {"engine": "ocaml-error", "ocaml": False, "error": str(e)}
+        return json.dumps(info), 200, {"Content-Type": "application/json"}
+
     @app.get("/sx/")
     async def sx_home():
         """SX docs home page."""