diff --git a/momentum_cli.py b/momentum_cli.py
index 32b22e9..ed19b34 100644
--- a/momentum_cli.py
+++ b/momentum_cli.py
@@ -138,9 +138,18 @@ def doctor():
     try:
         ev = _events_of(con, module="discovery", stage="completed")
         if ev:
-            m = json.loads(ev[0][2]).get("metrics", {})
-            _row(results, "discovery", "PASS",
-                 f"{len(m.get('universe', []))} sub-$20 names, {len(m.get('gappers', []))} gappers @ {ev[0][0]}")
+            payload = json.loads(ev[0][2])
+            m = payload.get("metrics", {})
+            n_uni, n_gap = len(m.get("universe", [])), len(m.get("gappers", []))
+            errs = payload.get("errors", [])
+            if n_uni == 0:
+                _row(results, "discovery", "FAIL",
+                     f"screener returned 0 names @ {ev[0][0]} — check Alpaca screener/limits"
+                     + (f"; {errs}" if errs else ""))
+            else:
+                _row(results, "discovery", "PASS" if not errs else "WARN",
+                     f"{n_uni} sub-$20 names, {n_gap} gappers @ {ev[0][0]}"
+                     + (f"; errors={errs}" if errs else ""))
         else:
             _row(results, "discovery", "WARN", "no discovery events yet (run the app)")
     except Exception as e:
diff --git a/research/ingestion/discovery.py b/research/ingestion/discovery.py
index ccbb994..1d556f8 100644
--- a/research/ingestion/discovery.py
+++ b/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:
diff --git a/research/ingestion/market_data.py b/research/ingestion/market_data.py
index 72ca1fb..238be09 100644
--- a/research/ingestion/market_data.py
+++ b/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 []
diff --git a/tests/unit/research/test_discovery.py b/tests/unit/research/test_discovery.py
new file mode 100644
index 0000000..817eb35
--- /dev/null
+++ b/tests/unit/research/test_discovery.py
@@ -0,0 +1,54 @@
+"""Discovery screener: top-cap + ETF/band filtering.
+
+Regression for the bug where screen_universe's top*2 headroom made
+discover_active_symbols request get_most_actives(top*3=120), exceeding Alpaca's
+hard cap of 100 -> HTTP 400 -> swallowed -> empty universe for a whole session.
+"""
+
+from research.ingestion.market_data import discover_active_symbols
+from research.ingestion.discovery import screen_universe, LEVERAGED_ETFS
+
+
+class _FakeScreener:
+    """Records the `top` it is asked for and prices a few fake symbols."""
+
+    PRICES = {"AAA": 5.0, "BBB": 500.0, "SOXL": 10.0, "CCC": 15.0, "DDD": 2.0}
+
+    def __init__(self):
+        self.last_top = None
+
+    def get_most_actives(self, top, by="volume"):
+        self.last_top = top
+        if top > 100:  # mirror Alpaca: reject top > 100
+            raise ValueError("invalid top: should not be larger than 100")
+        return [{"symbol": s} for s in self.PRICES]
+
+    def get_latest_trades(self, symbols):
+        return {s: {"p": self.PRICES[s]} for s in symbols if s in self.PRICES}
+
+
+def test_most_actives_top_never_exceeds_100():
+    fake = _FakeScreener()
+    # top=50 -> top*3=150 historically; must be capped to 100
+    out = discover_active_symbols(fake, top=50, price_min=1.0, price_max=20.0)
+    assert fake.last_top is not None and fake.last_top <= 100
+    assert out, "should return names, not swallow a 400 into []"
+
+
+def test_discover_active_symbols_filters_price_band():
+    fake = _FakeScreener()
+    out = discover_active_symbols(fake, top=10, price_min=1.0, price_max=20.0)
+    assert "BBB" not in out          # $500 is out of the $1-20 band
+    assert {"AAA", "CCC", "DDD"} <= set(out)
+
+
+def test_screen_universe_filters_leveraged_etfs():
+    fake = _FakeScreener()
+    out = screen_universe(fake, price_min=1.0, price_max=20.0, top=20)
+    assert "SOXL" in LEVERAGED_ETFS   # sanity: it's a known leveraged ETF
+    assert "SOXL" not in out          # ...and it's filtered out of the universe
+    assert "AAA" in out
+
+
+def test_screen_universe_empty_when_client_none():
+    assert screen_universe(None, 1.0, 20.0, 20) == []