diff --git a/data_only_viz/hand_features.py b/data_only_viz/hand_features.py
index 0144759..bb7650d 100644
--- a/data_only_viz/hand_features.py
+++ b/data_only_viz/hand_features.py
@@ -43,11 +43,21 @@ def _clamp(v: float, lo: float, hi: float) -> float:
 
 
 class HandFeatureExtractor:
-    def __init__(self, history: int = 5):
+    def __init__(self, history: int = 5, fist_enable: bool | None = None):
         self._history = max(2, history)
         # two routed slots (hand_slots.route_hands): 0 = user's left (L),
         # 1 = user's right (R); cx fallback when chirality is absent.
         self._buf = [deque(maxlen=self._history), deque(maxlen=self._history)]
+        # Master fist kill-switch: user-disabled live 2026-07-02 (too many
+        # false held-fist actions). fist stays 0.0 for BOTH hands whatever
+        # the per-slot fist_enabled kwarg says. FIST_ENABLE=1 re-enables.
+        # TODO: migrate the env read to VizConfig once config.py is free.
+        if fist_enable is None:
+            import os
+            fist_enable = os.environ.get("FIST_ENABLE", "0") not in (
+                "0", "", "false", "False",
+            )
+        self._fist_enable = fist_enable
 
     def _features(self, lm: list) -> dict:
         xs = [_finite(_coord(p, "x", 0), 0.5) for p in lm[:21]]
@@ -98,7 +108,7 @@ class HandFeatureExtractor:
 
         if left_lm is not None:
             lf = self._features(left_lm)
-            if not fist_enabled[0]:
+            if not (self._fist_enable and fist_enabled[0]):
                 lf["fist"] = 0.0
             lf["speed"] = self._speed(0, lf["cx"], lf["cy"])
             out_l = lf
@@ -107,7 +117,7 @@ class HandFeatureExtractor:
 
         if right_lm is not None:
             rf = self._features(right_lm)
-            if not fist_enabled[1]:
+            if not (self._fist_enable and fist_enabled[1]):
                 rf["fist"] = 0.0
             rf["speed"] = self._speed(1, rf["cx"], rf["cy"])
             out_r = rf
diff --git a/data_only_viz/tests/test_hand_features.py b/data_only_viz/tests/test_hand_features.py
index 30e69cd..4844ab1 100644
--- a/data_only_viz/tests/test_hand_features.py
+++ b/data_only_viz/tests/test_hand_features.py
@@ -117,19 +117,19 @@ def _fist_hand(tip_ext):
 
 
 def test_fist_all_fingers_curled():
-    out = HandFeatureExtractor().step([_fist_hand(0.20)])   # tips at knuckles
+    out = HandFeatureExtractor(fist_enable=True).step([_fist_hand(0.20)])   # tips at knuckles
     assert (out["L"] or out["R"])["fist"] > 0.9
 
 
 def test_open_hand_is_not_a_fist():
-    out = HandFeatureExtractor().step([_fist_hand(0.80)])   # fingers extended
+    out = HandFeatureExtractor(fist_enable=True).step([_fist_hand(0.80)])   # fingers extended
     assert (out["L"] or out["R"])["fist"] < 0.1
 
 
 def test_one_extended_finger_breaks_the_fist():
     h = _fist_hand(0.20)                                    # all curled...
     h[8] = LM(0.5 + 0.80 * 0.10, 0.5)                       # ...except the index
-    out = HandFeatureExtractor().step([h])
+    out = HandFeatureExtractor(fist_enable=True).step([h])
     assert (out["L"] or out["R"])["fist"] < 0.1            # min over fingers
 
 
@@ -171,7 +171,7 @@ def test_fist_enabled_false_zeroes_fist_preserves_openness():
 
 def test_fist_enabled_true_computes_fist():
     """fist_enabled=(True, True) leaves fist computation unchanged."""
-    ext = HandFeatureExtractor()
+    ext = HandFeatureExtractor(fist_enable=True)
     h = _fist_hand(0.20)
     out = ext.step([h], fist_enabled=(True, True))
     hand = out["L"] or out["R"]
@@ -225,3 +225,19 @@ def test_fist_enabled_per_slot_independence():
     assert out["L"]["fist"] == 0.0
     # R slot (cx~0.8) should compute normally (open -> fist < 0.1)
     assert out["R"]["fist"] < 0.1
+
+
+def test_fist_kill_switch_default_off(monkeypatch):
+    """FIST_ENABLE unset -> fist forced 0.0 even on a perfect fist
+    (user-disabled live 2026-07-02); continuous features unaffected."""
+    monkeypatch.delenv("FIST_ENABLE", raising=False)
+    out = HandFeatureExtractor().step([_fist_hand(0.20)])
+    hand = out["L"] or out["R"]
+    assert hand["fist"] == 0.0
+    assert hand["openness"] < 0.2
+
+
+def test_fist_kill_switch_env_reenable(monkeypatch):
+    monkeypatch.setenv("FIST_ENABLE", "1")
+    out = HandFeatureExtractor().step([_fist_hand(0.20)])
+    assert (out["L"] or out["R"])["fist"] > 0.9