fix: set_page_config before heavy import; cache_resource spinner; no-op patch

streamlit_app.py

@@ -1,22 +1,41 @@
 import streamlit as st
 import sys, os, traceback
 from pathlib import Path
-import importlib.util
+
+# Set page config immediately so the browser gets a response before the
+# heavy ML imports below.  demo/streamlit_app.py also calls set_page_config
+# at module level — we monkey-patch it to a no-op so the duplicate call
+# (on first import) doesn't raise a StreamlitAPIException.
+st.set_page_config(
+    page_title="SpindleFlow RL",
+    page_icon="⚡",
+    layout="wide",
+    initial_sidebar_state="collapsed",
+)
+_orig_spc = st.set_page_config
+st.set_page_config = lambda *a, **kw: None   # silence double-call from demo
 
 root = Path(__file__).resolve().parent
-sys.path.insert(0, str(root))
+demo_dir = root / "demo"
+for p in (str(root), str(demo_dir)):
+    if p not in sys.path:
+        sys.path.insert(0, p)
 os.chdir(str(root))
 
+
+@st.cache_resource(show_spinner="Loading SpindleFlow RL…")
+def _load_app():
+    """Cache the demo module so the 10–20 s ML import only happens once."""
+    import demo.streamlit_app as _app   # noqa: PLC0415
+    return _app
+
+
 try:
-    demo_file = root / "demo" / "streamlit_app.py"
-    spec = importlib.util.spec_from_file_location("spindleflow_demo", str(demo_file))
-    mod  = importlib.util.module_from_spec(spec)
-    mod.__file__ = str(demo_file)          # demo's own sys.path logic resolves correctly
-    sys.modules["spindleflow_demo"] = mod
-    spec.loader.exec_module(mod)           # runs demo/streamlit_app.py in its own context
-    mod.main()
+    st.set_page_config = _orig_spc      # restore before main() uses st.*
+    _app = _load_app()
+    _app.main()
 except SystemExit:
     pass
-except BaseException as e:
-    st.error(f"SpindleFlow failed to load: {e}")
+except Exception as exc:
+    st.error(f"SpindleFlow failed to load: {exc}")
     st.code(traceback.format_exc())