diff --git a/alembic/versions/010_add_setup_momentum_percentile.py b/alembic/versions/010_add_setup_momentum_percentile.py
new file mode 100644
index 0000000..d74a1df
--- /dev/null
+++ b/alembic/versions/010_add_setup_momentum_percentile.py
@@ -0,0 +1,34 @@
+"""add momentum_percentile to trade_setups
+
+The activation gate selects the top slice of the universe by 12-1 month momentum.
+That rank is computed across all tickers at scan time and stored on each setup so
+the live list, the Track Record's qualified stats, and outcome evaluation all gate
+on the same value (momentum as of the setup's detection).
+
+Revision ID: 010
+Revises: 009
+Create Date: 2026-06-23 00:00:00.000000
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision: str = "010"
+down_revision: Union[str, None] = "009"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "trade_setups",
+        sa.Column("momentum_percentile", sa.Float(), nullable=True),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("trade_setups", "momentum_percentile")
diff --git a/app/models/trade_setup.py b/app/models/trade_setup.py
index 24f9239..69f0e95 100644
--- a/app/models/trade_setup.py
+++ b/app/models/trade_setup.py
@@ -26,6 +26,9 @@ class TradeSetup(Base):
     )
 
     confidence_score: Mapped[float | None] = mapped_column(Float, nullable=True)
+    # Ticker's 12-1 momentum percentile across the universe at detection time
+    # (0–100, 100 = strongest). Drives the activation gate's core selection.
+    momentum_percentile: Mapped[float | None] = mapped_column(Float, nullable=True)
     targets_json: Mapped[str | None] = mapped_column(Text, nullable=True)
     conflict_flags_json: Mapped[str | None] = mapped_column(Text, nullable=True)
     recommended_action: Mapped[str | None] = mapped_column(String(20), nullable=True)
diff --git a/app/schemas/trade_setup.py b/app/schemas/trade_setup.py
index 4445b6a..109a763 100644
--- a/app/schemas/trade_setup.py
+++ b/app/schemas/trade_setup.py
@@ -48,4 +48,5 @@ class TradeSetupResponse(BaseModel):
     outcome_date: date | None = None
     evaluated_at: datetime | None = None
     current_price: float | None = None
+    momentum_percentile: float | None = None
     recommendation_summary: RecommendationSummaryResponse | None = None
diff --git a/app/services/backtest_service.py b/app/services/backtest_service.py
index f0d9bad..89251e3 100644
--- a/app/services/backtest_service.py
+++ b/app/services/backtest_service.py
@@ -580,11 +580,14 @@ def _assign_momentum_percentiles(candidates: list[dict]) -> None:
 
 def _momentum_qualifies(cand: dict, threshold: float) -> bool:
     """Whether a candidate clears the floors (meets_core) and the momentum gate.
-    Threshold 0 disables the momentum gate (floors only)."""
+    Threshold 0 disables the momentum gate (floors only). The gate is long-only:
+    while it's active, shorts (fighting the trend) never qualify."""
     if not cand["meets_core"]:
         return False
     if threshold <= 0:
         return True
+    if cand["direction"] == "short":
+        return False
     mp = cand.get("momentum_percentile")
     return mp is not None and mp >= threshold
 
diff --git a/app/services/momentum_service.py b/app/services/momentum_service.py
new file mode 100644
index 0000000..569ff73
--- /dev/null
+++ b/app/services/momentum_service.py
@@ -0,0 +1,63 @@
+"""Cross-sectional 12-1 momentum ranking for the universe.
+
+The activation gate selects the top ``min_momentum_percentile`` of the universe
+by 12-1 month momentum (return from ~12 months ago to ~1 month ago — the one
+price signal the backtest showed sorts forward returns). The daily scan ranks
+every ticker and stores each setup's percentile (see ``rr_scanner_service``), so
+the live list, the Track Record's qualified stats, and outcome evaluation all gate
+on the same value.
+"""
+
+from __future__ import annotations
+
+import json
+import logging
+
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.models.ticker import Ticker
+from app.services.price_service import query_ohlcv
+
+logger = logging.getLogger(__name__)
+
+# 12-1 momentum: ~12 months of daily history (252 bars) with the last ~1 month
+# (21 bars) skipped. Matches the backtest's _signal_values / _window_setups.
+_MOM_LOOKBACK = 252
+_MOM_SKIP = 21
+
+
+def compute_12_1_momentum(closes: list[float]) -> float | None:
+    """Return over the window ending ~1 month ago, starting ~12 months ago.
+    None when there isn't a full year of history."""
+    if len(closes) >= _MOM_LOOKBACK + 1 and closes[-(_MOM_LOOKBACK + 1)] > 0:
+        return closes[-(_MOM_SKIP + 1)] / closes[-(_MOM_LOOKBACK + 1)] - 1.0
+    return None
+
+
+async def compute_momentum_percentiles(db: AsyncSession) -> dict[str, float]:
+    """Compute each ticker's 12-1 momentum and rank the universe into a
+    ``{symbol: percentile}`` map (0–100, 100 = strongest momentum). Tickers
+    without a full year of history are absent (can't be ranked)."""
+    result = await db.execute(select(Ticker).order_by(Ticker.symbol))
+    tickers = list(result.scalars().all())
+
+    momentum: dict[str, float] = {}
+    for ticker in tickers:
+        try:
+            records = await query_ohlcv(db, ticker.symbol)
+        except Exception:
+            logger.exception("Momentum fetch failed for %s", ticker.symbol)
+            continue
+        m = compute_12_1_momentum([float(r.close) for r in records])
+        if m is not None:
+            momentum[ticker.symbol] = m
+
+    ranked = sorted(momentum, key=lambda s: momentum[s])
+    n = len(ranked)
+    percentiles = {
+        sym: round((rank / (n - 1) * 100.0) if n > 1 else 100.0, 2)
+        for rank, sym in enumerate(ranked)
+    }
+    logger.info(json.dumps({"event": "momentum_ranked", "tickers": n}))
+    return percentiles
diff --git a/app/services/qualification.py b/app/services/qualification.py
index 54ed0fc..9949fed 100644
--- a/app/services/qualification.py
+++ b/app/services/qualification.py
@@ -67,11 +67,15 @@ def setup_qualifies(setup: Any, config: dict) -> bool:
     if (setup.confidence_score or 0.0) < config["min_confidence"]:
         return False
     # Cross-sectional momentum: the core selection. A setup's ticker must rank in
-    # the top ``min_momentum_percentile`` of the universe by 12-1 momentum. Only
-    # enforced when a percentile is attached (live setups / backtest) and a
-    # threshold is set; callers that don't attach it defer to the floors above.
+    # the top ``min_momentum_percentile`` of the universe by 12-1 momentum. The
+    # validated edge is long-only, so while the gate is active shorts (which fight
+    # the trend) never qualify. The percentile floor is only enforced when a
+    # percentile is attached (live setups / backtest); callers that don't attach
+    # it defer to the floors above.
     min_pct = float(config.get("min_momentum_percentile", 0.0))
     if min_pct > 0:
+        if (getattr(setup, "direction", "long") or "long") == "short":
+            return False
         momentum_percentile = getattr(setup, "momentum_percentile", None)
         if momentum_percentile is not None and momentum_percentile < min_pct:
             return False
diff --git a/app/services/rr_scanner_service.py b/app/services/rr_scanner_service.py
index 0f3dfcd..d4f0103 100644
--- a/app/services/rr_scanner_service.py
+++ b/app/services/rr_scanner_service.py
@@ -81,8 +81,13 @@ async def scan_ticker(
     symbol: str,
     rr_threshold: float = 1.5,
     atr_multiplier: float = 1.5,
+    momentum_percentile: float | None = None,
 ) -> list[TradeSetup]:
-    """Scan a single ticker for trade setups meeting the R:R threshold."""
+    """Scan a single ticker for trade setups meeting the R:R threshold.
+
+    ``momentum_percentile`` is the ticker's 12-1 momentum rank across the universe
+    (computed by the caller), stored on each setup so the activation gate can
+    select the top slice."""
     ticker = await _get_ticker(db, symbol)
 
     records = await query_ohlcv(db, symbol)
@@ -169,6 +174,7 @@ async def scan_ticker(
                     rr_ratio=round(best_candidate_rr, 4),
                     composite_score=round(composite_score, 4),
                     detected_at=now,
+                    momentum_percentile=momentum_percentile,
                 ))
 
     if levels_below:
@@ -202,6 +208,7 @@ async def scan_ticker(
                     rr_ratio=round(best_candidate_rr, 4),
                     composite_score=round(composite_score, 4),
                     detected_at=now,
+                    momentum_percentile=momentum_percentile,
                 ))
 
     available_directions = {s.direction for s in setups}
@@ -249,6 +256,16 @@ async def scan_all_tickers(
     tickers = list(result.scalars().all())
     total = len(tickers)
 
+    # Rank the universe by 12-1 momentum up front so each new setup carries its
+    # ticker's percentile (used by the activation gate). Best-effort.
+    try:
+        from app.services import momentum_service
+
+        percentiles = await momentum_service.compute_momentum_percentiles(db)
+    except Exception:
+        logger.exception("Momentum ranking refresh failed")
+        percentiles = {}
+
     all_setups: list[TradeSetup] = []
     for index, ticker in enumerate(tickers):
         if progress_callback is not None:
@@ -267,7 +284,8 @@ async def scan_all_tickers(
                 logger.exception("Error refreshing scores for %s", ticker.symbol)
 
             setups = await scan_ticker(
-                db, ticker.symbol, rr_threshold, atr_multiplier
+                db, ticker.symbol, rr_threshold, atr_multiplier,
+                momentum_percentile=percentiles.get(ticker.symbol),
             )
             all_setups.extend(setups)
         except Exception:
@@ -410,4 +428,5 @@ def _trade_setup_to_dict(setup: TradeSetup, symbol: str, current_price: float |
         "outcome_date": setup.outcome_date,
         "evaluated_at": setup.evaluated_at,
         "current_price": current_price,
+        "momentum_percentile": setup.momentum_percentile,
     }
diff --git a/frontend/src/lib/qualification.ts b/frontend/src/lib/qualification.ts
index d366c87..4f35dc0 100644
--- a/frontend/src/lib/qualification.ts
+++ b/frontend/src/lib/qualification.ts
@@ -33,11 +33,14 @@ export function qualifiesSetup(setup: TradeSetup, config: ActivationConfig): boo
     return false;
   }
   if ((setup.confidence_score ?? 0) < config.min_confidence) return false;
-  // Cross-sectional momentum is the core selection — only enforced when a
-  // percentile is attached and a threshold is set; otherwise defer to the floors.
-  if (config.min_momentum_percentile > 0 && setup.momentum_percentile != null
-      && setup.momentum_percentile < config.min_momentum_percentile) {
-    return false;
+  // Cross-sectional momentum is the core selection (long-only). While the gate is
+  // active, shorts never qualify; the percentile floor is enforced only when a
+  // percentile is attached, otherwise defer to the floors.
+  if (config.min_momentum_percentile > 0) {
+    if (setup.direction === 'short') return false;
+    if (setup.momentum_percentile != null && setup.momentum_percentile < config.min_momentum_percentile) {
+      return false;
+    }
   }
   if (config.require_high_conviction && !HIGH_CONVICTION_ACTIONS.has(setup.recommended_action ?? '')) {
     return false;
diff --git a/tests/unit/test_momentum_service.py b/tests/unit/test_momentum_service.py
new file mode 100644
index 0000000..b69556e
--- /dev/null
+++ b/tests/unit/test_momentum_service.py
@@ -0,0 +1,71 @@
+"""Unit tests for the cross-sectional 12-1 momentum ranking."""
+
+from __future__ import annotations
+
+from datetime import date, timedelta
+
+import pytest
+
+from app.models.ohlcv import OHLCVRecord
+from app.models.ticker import Ticker
+from app.services import momentum_service as ms
+
+
+@pytest.fixture
+async def session():
+    from tests.conftest import _test_session_factory
+
+    async with _test_session_factory() as s:
+        yield s
+
+
+async def _seed(session, symbol: str, rate: float, n: int = 280) -> None:
+    t = Ticker(symbol=symbol)
+    session.add(t)
+    await session.flush()
+    base = date(2024, 1, 1)
+    for i in range(n):
+        close = 100.0 * (rate ** i)
+        session.add(OHLCVRecord(
+            ticker_id=t.id,
+            date=base + timedelta(days=i),
+            open=close, high=close, low=close, close=close,
+            volume=1_000_000,
+        ))
+    await session.commit()
+
+
+def test_compute_momentum_insufficient_history():
+    assert ms.compute_12_1_momentum([100.0] * 100) is None
+
+
+def test_compute_momentum_value():
+    closes = [100.0 * (1.01 ** i) for i in range(300)]
+    m = ms.compute_12_1_momentum(closes)
+    # 12-1 momentum skips the last month: close[-22] / close[-253] - 1
+    assert m == closes[-22] / closes[-253] - 1.0
+    assert m > 0
+
+
+async def test_ranks_universe_into_percentiles(session):
+    await _seed(session, "HIGH", rate=1.010)   # strong uptrend → top momentum
+    await _seed(session, "MID", rate=1.002)
+    await _seed(session, "LOW", rate=0.999)     # declining → bottom momentum
+
+    pct = await ms.compute_momentum_percentiles(session)
+    assert pct["HIGH"] == 100.0
+    assert pct["MID"] == 50.0
+    assert pct["LOW"] == 0.0
+
+
+async def test_short_history_ticker_is_unranked(session):
+    await _seed(session, "LONG", rate=1.005)
+    await _seed(session, "SHORTHX", rate=1.005, n=100)  # < 1y → no momentum
+
+    pct = await ms.compute_momentum_percentiles(session)
+    assert "LONG" in pct
+    assert "SHORTHX" not in pct
+
+
+async def test_empty_universe_returns_empty(session):
+    assert await ms.compute_momentum_percentiles(session) == {}
diff --git a/tests/unit/test_qualification.py b/tests/unit/test_qualification.py
index ca986fc..9338229 100644
--- a/tests/unit/test_qualification.py
+++ b/tests/unit/test_qualification.py
@@ -90,6 +90,15 @@ class TestMomentumGate:
         legacy = {k: v for k, v in DEFAULT_GATE.items() if k != "min_momentum_percentile"}
         assert setup_qualifies(_setup(momentum_percentile=10.0), legacy) is True
 
+    def test_short_excluded_when_gate_active(self):
+        # The momentum edge is long-only — a short never qualifies while the gate
+        # is on, even on a top-momentum name.
+        assert setup_qualifies(_setup(direction="short", momentum_percentile=95.0), MOMENTUM_GATE) is False
+
+    def test_short_allowed_when_gate_off(self):
+        # With the momentum gate disabled, shorts pass on the floors as before.
+        assert setup_qualifies(_setup(direction="short", momentum_percentile=10.0), DEFAULT_GATE) is True
+
 
 class TestStrictTighteners:
     def test_clean_high_conviction_passes(self):