Add Oracle health pre-check in run_pre_screen to warn before bar-fetch timeout

If Oracle is unreachable at 09:20 ET, without this check the pre-screen silently
waits through 5 chunks × 15s timeout (75s) before logging the empty-bars warning.
The new 3s probe logs a CRITICAL warning immediately so the operator can restart
Oracle before the market opens.

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

apps/orb_trader/engine.py

@@ -129,6 +129,22 @@ class ORBTradingEngine:
             self._session.session_id, date_str, phase="pre_screen"
         )
 
+        # Cheap Oracle health probe — warns early so the operator can restart Oracle
+        # before the bar-fetch loop (5 chunks × 15s timeout) burns 75s silently.
+        try:
+            import httpx as _httpx
+            from libs.oracle_client.alpaca import _base_url as _oracle_base_url
+            _oracle_health_url = _oracle_base_url() + "/api/v1/health"
+            _r = _httpx.get(_oracle_health_url, timeout=3.0)
+            _ok = _r.status_code < 400
+        except Exception:
+            _ok = False
+        if not _ok:
+            self._log(
+                "CRITICAL: Oracle is unreachable — bar fetches will likely fail. "
+                "Start Oracle before 09:20 ET on live trading days."
+            )
+
         universe_source = getattr(self._params, "_universe_source", "midlarge")
         universe_symbols_file = getattr(self._params, "_universe_symbols_file", None)
         tickers = load_universe(universe_source, universe_symbols_file)