diff --git a/src/pf1e_simulator/combat.py b/src/pf1e_simulator/combat.py
index fe2dc33..c70746d 100644
--- a/src/pf1e_simulator/combat.py
+++ b/src/pf1e_simulator/combat.py
@@ -1066,7 +1066,6 @@ class CombatEngine:
                 source="maneuver: trip",
             )
         )
-        target.conditions.append(CONDITIONS_BY_NAME["prone"])
         self._log(
             f"round {self._current_round} {state.combatant.id}: trip vs "
             f"{target.combatant.id} d20={m.roll}+{m.attacker_cmb}={m.total} "
@@ -1136,7 +1135,6 @@ class CombatEngine:
                 source=f"maneuver: grapple by {state.combatant.id}",
             )
         )
-        target.conditions.append(CONDITIONS_BY_NAME["grappled"])
         target.grappled_with = state.combatant.id
         state.grappled_with = target.combatant.id
         self._log(
@@ -1304,7 +1302,6 @@ class CombatEngine:
                 source=f"hex: evil_eye by {state.combatant.id}",
             )
         )
-        target.conditions.append(CONDITIONS_BY_NAME["shaken"])
         self._log(
             f"round {self._current_round} {state.combatant.id}: evil eye on "
             f"{target.combatant.id} -> shaken (1r)"
@@ -1328,7 +1325,6 @@ class CombatEngine:
                 source=f"hex: slumber by {state.combatant.id}",
             )
         )
-        target.conditions.append(CONDITIONS_BY_NAME["asleep"])
         self._log(
             f"round {self._current_round} {state.combatant.id}: slumber on "
             f"{target.combatant.id} -> asleep (1r)"
@@ -1452,11 +1448,6 @@ class CombatEngine:
                     source=f"inspire courage by {state.combatant.id}",
                 )
             )
-            # Also update old effects field for backwards compatibility
-            ally.effects.extend((
-                StatModifier(target="attack", value=1, bonus_type="morale"),
-                StatModifier(target="damage", value=1, bonus_type="morale"),
-            ))
         self._log(
             f"round {self._current_round} {state.combatant.id}: "
             f"inspire courage +1 morale attack/damage to {len(affected)} allies"
@@ -1665,7 +1656,6 @@ class CombatEngine:
                 source=f"spell: {spell_name}",
             )
         )
-        target.conditions.append(cond)
         return f"{effect.condition_name} ({effect.duration_rounds}r)"
 
     def _apply_heal_effect(
@@ -1696,7 +1686,6 @@ class CombatEngine:
                 source=f"spell: {spell_name}",
             )
         )
-        target.effects.extend(effect.modifiers)
         return f"buff {len(effect.modifiers)} mods ({effect.duration_rounds}r)"
 
     def _apply_area_effect(
diff --git a/tests/test_spells.py b/tests/test_spells.py
index 8e3c2b9..a14313e 100644
--- a/tests/test_spells.py
+++ b/tests/test_spells.py
@@ -255,14 +255,14 @@ class TestHoldPerson:
         target = _make_target()
         engine, c, t = _make_engine(caster, target, [2])
         engine._cast_spell(c, t, "Hold Person")
-        assert any(cond.name == "paralyzed" for cond in t.conditions)
+        assert any(ac.condition.name == "paralyzed" for ac in t.active_conditions)
 
     def test_successful_save_no_condition(self) -> None:
         caster = _make_caster()
         target = _make_target()
         engine, c, t = _make_engine(caster, target, [20])
         engine._cast_spell(c, t, "Hold Person")
-        assert not any(cond.name == "paralyzed" for cond in t.conditions)
+        assert not any(ac.condition.name == "paralyzed" for ac in t.active_conditions)
 
     def test_transcript_shows_negated_on_save(self) -> None:
         caster = _make_caster()
@@ -282,7 +282,7 @@ class TestFear:
         target = _make_target()
         engine, c, t = _make_engine(caster, target, [2])
         engine._cast_spell(c, t, "Fear")
-        assert any(cond.name == "frightened" for cond in t.conditions)
+        assert any(ac.condition.name == "frightened" for ac in t.active_conditions)
 
 
 class TestCureLightWounds:
@@ -317,8 +317,9 @@ class TestBullsStrength:
         target = _make_target()
         engine, c, t = _make_engine(caster, target, [3, 3], target_pos=(1, 0))
         engine._cast_spell(c, t, "Bull's Strength")
-        atk_mods = [e for e in t.effects if e.target == "attack"]
-        dmg_mods = [e for e in t.effects if e.target == "damage"]
+        buff_mods = [m for b in t.active_buffs for m in b.modifiers]
+        atk_mods = [e for e in buff_mods if e.target == "attack"]
+        dmg_mods = [e for e in buff_mods if e.target == "damage"]
         assert len(atk_mods) == 1
         assert len(dmg_mods) == 1
         assert atk_mods[0].value == 1
@@ -461,3 +462,20 @@ class TestSpellSlots:
         engine._cast_spell(c, t, "Magic Missile")  # spends the only level-1 slot
         assert c.spell_slots_left[1] == 0
         assert _choose_spell_action(engine, c, t) is None
+
+
+class TestActiveIsSingleSource:
+    """Given: active_* is the single source of truth for conditions and buffs
+    When: _cast_spell applies a condition and a buff
+    Then: the legacy conditions/effects lists stay empty while the active_* lists are populated."""
+
+    def test_legacy_lists_stay_empty_active_lists_populated(self) -> None:
+        caster = _make_caster()
+        target = _make_target()
+        engine, c, t = _make_engine(caster, target, [2, 3, 3], target_pos=(1, 0))
+        engine._cast_spell(c, t, "Hold Person")
+        engine._cast_spell(c, t, "Bull's Strength")
+        assert t.conditions == []
+        assert t.effects == []
+        assert any(ac.condition.name == "paralyzed" for ac in t.active_conditions)
+        assert any(b.source.startswith("spell:") for b in t.active_buffs)