Harden discovery: surface screener failures + regression test

- discover_active_symbols logs the screener error instead of swallowing silently.
- run_discovery records an explicit error when the universe is empty (surfaces in
  the discovery event + Grafana).
- momentum doctor now FAILs when the latest discovery universe is 0 (the morning's
  dead screener would have shown red within a minute).
- tests/unit/research/test_discovery.py: pins get_most_actives top<=100 and the
  ETF/price-band filtering.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

research/ingestion/discovery.py

@@ -168,6 +168,12 @@ def run_discovery(
     for ticker in result.news:
         if ticker not in result.universe:
             result.universe.append(ticker)
+    if not result.universe:
+        # Make a dead screener LOUD (this was silent for a whole session once):
+        # surfaces in the discovery event's errors and `momentum doctor`.
+        result.errors.append(
+            "screener returned 0 names (Alpaca cap/limit, or no qualifying movers)"
+        )
 
     # Backfill daily history for the universe so gap%/RVOL have a baseline.
     if backfill_daily and result.universe and client is not None:

research/ingestion/market_data.py

@@ -13,6 +13,7 @@ hardcoded ``is_regular_hours = TRUE`` on every row. Here we:
 
 from __future__ import annotations
 
+import logging
 from dataclasses import dataclass, field
 from datetime import date, datetime, time, timedelta, timezone
 from zoneinfo import ZoneInfo
@@ -23,6 +24,8 @@ REGULAR_CLOSE = time(16, 0)
 PREMARKET_OPEN = time(4, 0)
 AFTERHOURS_CLOSE = time(20, 0)
 
+logger = logging.getLogger(__name__)
+
 
 def classify_session(ts_utc: datetime) -> tuple[date, bool, bool, bool]:
     """Return (session_date, is_premarket, is_regular_hours, is_afterhours)."""
@@ -251,5 +254,6 @@ def discover_active_symbols(
             if len(in_band) >= top:
                 break
         return in_band
-    except Exception:  # noqa: BLE001 - screener needs a paid feed sometimes
+    except Exception as exc:  # noqa: BLE001 - screener needs a paid feed sometimes
+        logger.warning("most-actives screener failed: %s", exc)
         return []