diff --git a/src/pf1e_simulator/combat.py b/src/pf1e_simulator/combat.py
index cf1adf6..69bfb32 100644
--- a/src/pf1e_simulator/combat.py
+++ b/src/pf1e_simulator/combat.py
@@ -1396,7 +1396,7 @@ class CombatEngine:
     def _hex_cackle(self, state: CombatantState, target: CombatantState) -> None:
         """Cackle: prolong one hex by 1 round (extends all hex conditions)."""
         extended = False
-        for ac in target.active_conditions:
+        for ac in list(target.active_conditions):
             if ac.source.startswith("hex:"):
                 target.active_conditions.remove(ac)
                 target.active_conditions.append(
diff --git a/tests/test_cackle.py b/tests/test_cackle.py
new file mode 100644
index 0000000..e5b7549
--- /dev/null
+++ b/tests/test_cackle.py
@@ -0,0 +1,139 @@
+"""Tests for the cackle hex: bound the extension of hex conditions (Task 9).
+
+Cackle must extend exactly one +1 round per pre-existing hex condition, in a
+single pass, without re-extending the replacements it appends. The pre-fix code
+mutated ``target.active_conditions`` (remove/append) while iterating it, which
+grew the list unboundedly and looped forever.
+"""
+
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+from pf1e_simulator.combat import CombatantState, CombatEngine
+from pf1e_simulator.conditions import CONDITIONS_BY_NAME
+from pf1e_simulator.dice import parse_dice
+from pf1e_simulator.effects import ActiveCondition
+from pf1e_simulator.grid import Grid
+from pf1e_simulator.map import MapSpec, TerrainType
+from pf1e_simulator.models import (
+    AbilityScores,
+    ACProfile,
+    AttackSpec,
+    Combatant,
+    DamageComponent,
+    Saves,
+)
+from pf1e_simulator.rng import ScriptedRng
+
+if TYPE_CHECKING:
+    from collections.abc import Collection
+
+_HEX_SOURCES = ("hex: evil_eye by caster", "hex: evil_eye by caster-2")
+_ROUNDS_BEFORE = (2, 1)
+
+
+def _make_witch(cid: str = "caster") -> Combatant:
+    attack = AttackSpec(
+        id=f"{cid}-w",
+        name="dagger",
+        kind="melee",
+        attack_bonus=2,
+        damage=[DamageComponent(formula=parse_dice("1d4"), types=["piercing"])],
+    )
+    return Combatant(
+        id=cid,
+        name=cid,
+        level=5,
+        size="Medium",
+        abilities=AbilityScores(
+            str_score=10, dex_score=14, con_score=12,
+            int_score=18, wis_score=12, cha_score=10,
+        ),
+        hp_max=20,
+        ac=ACProfile(total=12, touch=12, flat_footed=10),
+        bab=2,
+        initiative_mod=2,
+        speed_land_ft=30,
+        saves=Saves(fort=3, ref=4, will=4),
+        attacks=[attack],
+        casting_ability="int",
+        spell_slots={1: 4},
+        resources={"hexes": 3},
+    )
+
+
+def _make_target(cid: str = "target") -> Combatant:
+    attack = AttackSpec(
+        id=f"{cid}-w",
+        name="club",
+        kind="melee",
+        attack_bonus=3,
+        damage=[DamageComponent(formula=parse_dice("1d6"), types=["bludgeoning"])],
+    )
+    return Combatant(
+        id=cid,
+        name=cid,
+        level=1,
+        size="Medium",
+        abilities=AbilityScores(
+            str_score=10, dex_score=10, con_score=10,
+            int_score=10, wis_score=10, cha_score=10,
+        ),
+        hp_max=30,
+        ac=ACProfile(total=10, touch=10, flat_footed=10),
+        bab=1,
+        initiative_mod=0,
+        speed_land_ft=30,
+        saves=Saves(fort=2, ref=2, will=2),
+        attacks=[attack],
+    )
+
+
+def _make_engine() -> tuple[CombatEngine, CombatantState, CombatantState]:
+    c = CombatantState(
+        combatant=_make_witch(), side="players", pos=(0, 0), hp=20,
+        resources_left={"hexes": 3},
+    )
+    t = CombatantState(
+        combatant=_make_target(), side="monsters", pos=(3, 0), hp=30,
+    )
+    legend = {".": TerrainType(type="floor", move_cost=1)}
+    spec = MapSpec(name="test", terrain=tuple(["." * 8] * 8), legend=legend)
+    engine = CombatEngine(ScriptedRng([]), Grid.from_spec(spec), [c, t])
+    return engine, c, t
+
+
+def _seed_hex_conditions(target: CombatantState) -> dict[str, int]:
+    target.active_conditions = [
+        ActiveCondition(
+            condition=CONDITIONS_BY_NAME["shaken"],
+            rounds_left=rounds,
+            source=source,
+        )
+        for source, rounds in zip(_HEX_SOURCES, _ROUNDS_BEFORE, strict=True)
+    ]
+    return dict(zip(_HEX_SOURCES, _ROUNDS_BEFORE, strict=True))
+
+
+def _rounds_by_source(conditions: Collection[ActiveCondition]) -> dict[str, int]:
+    return {ac.source: ac.rounds_left for ac in conditions}
+
+
+class TestCackleExtendsHexOnce:
+    """Given: a target carrying 2 pre-existing hex conditions (2 Evil Eyes,
+    rounds_left 2 and 1)
+    When: the witch cackles
+    Then: EXACTLY 2 extensions of +1 round happen — each hex's rounds_left
+    rises by 1, the total hex-condition count stays 2 (no growth), and the
+    call terminates (the pre-fix loop never did)."""
+
+    def test_exactly_two_hex_extensions_of_one_round(self) -> None:
+        engine, c, t = _make_engine()
+        expected = _seed_hex_conditions(t)
+
+        engine._hex_cackle(c, t)
+
+        after = _rounds_by_source(t.active_conditions)
+        assert len(after) == 2
+        assert after == {source: rounds + 1 for source, rounds in expected.items()}