fix(rules): stabilize a dying creature when healed

PF1e (CRB, Stable Characters and Recovery): any healing that cures a
dying creature of even 1 point makes it stable. _apply_heal_effect and
_channel_heal now set stabilized_hp when the healed hp stays negative,
so the creature stops losing 1 hp per round.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/pf1e_simulator/combat.py

@@ -4622,6 +4622,11 @@ class CombatEngine:
     ) -> None:
         old_hp = affected_state.hp
         affected_state.hp = min(affected_state.hp + dmg, affected_state.combatant.hp_max)
+        # PF1e (CRB, Stable Characters and Recovery): "If any sort of healing
+        # cures the dying character of even 1 point of damage, he becomes
+        # stable and stops losing hit points."
+        if affected_state.hp < 0:
+            affected_state.stabilized_hp = affected_state.hp
         actual = affected_state.hp - old_hp
         self._stats[state.combatant.id].damage_dealt += actual
         self._stop_bleeding(affected_state)
@@ -5503,6 +5508,11 @@ class CombatEngine:
             heal = int(heal * 1.5)
         old_hp = target.hp
         target.hp = min(target.hp + heal, target.combatant.hp_max)
+        # PF1e (CRB, Stable Characters and Recovery): "If any sort of healing
+        # cures the dying character of even 1 point of damage, he becomes
+        # stable and stops losing hit points."
+        if target.hp < 0:
+            target.stabilized_hp = target.hp
         actual = target.hp - old_hp
         self._stop_bleeding(target)
         return f"+{actual} HP"

tests/test_dying_and_crits.py

@@ -13,6 +13,7 @@ from pf1e_simulator.models import (
     Saves,
 )
 from pf1e_simulator.rng import ScriptedRng
+from pf1e_simulator.spells import HealEffect
 from tests.test_observation_enriched import _snapshot, make_grid, make_state
 
 
@@ -212,6 +213,52 @@ def test_dying_with_bleed_reaches_death_faster_than_without() -> None:
     assert not plain.dead
 
 
+def test_heal_spell_stabilizes_dying_creature() -> None:
+    # PF1e (CRB, Stable Characters and Recovery): healing a dying creature for
+    # even 1 point makes it stable — it stops losing 1 hp per round.
+    eng, s = _solo(con_score=10)
+    s.hp = -3
+    eng._rng = ScriptedRng([1])  # 1d8 -> 1: only 1 point cured
+    result = eng._apply_heal_effect(
+        HealEffect(formula=parse_dice("1d8")), s, empower=False, maximize=False
+    )
+    assert result == "+1 HP"
+    assert s.hp == -2
+    assert s.stabilized_hp == -2
+    # Stable: the dying slot consumes no roll and loses no hp.
+    eng._rng = ScriptedRng([])
+    eng._process_dying(s)
+    assert s.hp == -2
+    assert s.stabilized_hp == -2
+
+
+def test_channel_heal_stabilizes_dying_creature() -> None:
+    eng, s = _solo(con_score=10)
+    channeler = eng._states[0]
+    s.hp = -3
+    eng._channel_heal(channeler, s, 1)  # exactly 1 point cured
+    assert s.hp == -2
+    assert s.stabilized_hp == -2
+    eng._rng = ScriptedRng([])
+    eng._process_dying(s)
+    assert s.hp == -2
+
+
+def test_heal_to_positive_hp_does_not_stabilize() -> None:
+    # Healed back to consciousness there is no dying state to stabilize; the
+    # next drop starts dying from scratch (stabilized_hp stays None at hp >= 0).
+    eng, s = _solo(con_score=10)
+    s.hp = -3
+    eng._rng = ScriptedRng([8])
+    eng._apply_heal_effect(
+        HealEffect(formula=parse_dice("1d8")), s, empower=False, maximize=False
+    )
+    assert s.hp == 5
+    assert s.stabilized_hp is None
+    eng._process_dying(s)
+    assert s.stabilized_hp is None
+
+
 def test_dying_tick_runs_on_initiative_slot_during_round() -> None:
     # m1 is downed before the battle starts; both sides still have active
     # members so the battle continues and m1's slot processes the dying check.