fix(spells): apply a shaken effect when a fear save succeeds

ConditionEffect gains save_partial (JSON 'on_success': condition_name + duration_rounds). On a successful save that would otherwise negate, _apply_condition_effect now imposes the weaker condition (SRD fear.md: panicked on a failed Will save, shaken for 1 round on a success). Extended _metamagic_transform_sub to preserve/double it; extracted _impose_condition helper. Updated fear.json, added failed/successful-save and loader tests in test_spells.py, and the README.

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

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

README.md

@@ -1254,6 +1254,13 @@ Règles modélisées :
    dégâts peut déclarer `save_negates: false` (conformance D1 — SRD
    « Sound Burst » : « Fortitude partial » n'annule que l'étourdissement,
     jamais les dés) : la sauvegarde réussie ne réduit alors pas ces dégâts.
+    **Sauvegardes partielles (S2d)** : un `ConditionEffect` peut déclarer
+    `"on_success": {"condition_name": "shaken", "duration_rounds": 1}` (champ
+    `save_partial`) — sur une sauvegarde **réussie**, au lieu d'annuler
+    totalement l'effet, la cible subit la condition affaiblie indiquée (SRD
+    Fear : paniqué à l'échec, `shaken` 1 round au succès). Sans `on_success`,
+    le comportement reste « sauvegarde annule ». L'Extend Spell double aussi la
+    durée de la condition partielle.
 - Dons : les 8 PJ portent 55 noms de dons uniques ; le chargeur résout chacun d'eux
   soit vers un effet réel (Power Attack actif, Weapon Focus ciblé par arme, Toughness
   lié au niveau, dons passifs via `_stat_modifiers`), soit vers un « no-op » tracé en
@@ -1431,16 +1438,14 @@ plutôt que bricolées) :
   minuscules sur une même case) ne sont pas modélisées ; seule la substitution
   Dextérité/Force du CMB (conformance L1) tient compte de leur taille.
 
-Limites de sorts (conformance D6-D9, documentées plutôt que bricolées — le
-moteur n'a pas encore de sauvegarde partielle) :
+Limites de sorts (conformance D6-D9, documentées plutôt que bricolées) :
 
-- **Fear — sauvegarde totale** (SRD spells/fear.md : « each
-  living creature in the area [...] becomes panicked unless it succeeds on a
-  Will save [...]. If the Will save succeeds, the creature is shaken for 1
-  round » ; cône de 30 ft — modélisé, S1a/S1c) : la condition appliquée est
-  bien `panicked` (conformance D8), mais le moteur n'a pas de sauvegarde
-  partielle pour les conditions — un succès annule totalement l'effet au lieu
-  de poser `shaken` 1 round ; la durée « 1 round/niveau » est fixée à 4 rounds.
+- **Fear — durée figée** (SRD spells/fear.md : « each living creature in the
+  area [...] becomes panicked unless it succeeds on a Will save [...]. If the
+  Will save succeeds, the creature is shaken for 1 round » ; cône de 30 ft —
+  modélisé, S1a/S1c) : la sauvegarde partielle est désormais modélisée (panic
+  à l'échec, `shaken` 1 round au succès — voir « Sauvegardes partielles » plus
+  bas) ; seule la durée « 1 round/niveau » du `panicked` reste fixée à 4 rounds.
 - **Résistance aux sorts appliquée à tout sort ciblé** : le moteur oppose la
   SR du combattant à chaque sort qui le cible, sans drapeau par sort ; les
   rares sorts dont la fiche SRD déclare « Spell Resistance: no » (ex. Acid

data/spells/fear.json

@@ -17,10 +17,11 @@
           "type": "condition",
           "condition_name": "panicked",
           "duration_rounds": 4,
-          "save_negates": true
+          "save_negates": true,
+          "on_success": { "condition_name": "shaken", "duration_rounds": 1 }
         }
       ]
     }
   ],
-  "description": "SRD spells/fear.md: each living creature in the 30-ft. cone becomes panicked unless it succeeds on a Will save (a successful save makes it shaken for 1 round instead). Modeled as panicked for 4 rounds on a failed save; the shaken-on-success partial needs partial-save support (documented limitation). The SRD range is 30 ft. - modeled as the closest category (close)."
+  "description": "SRD spells/fear.md: each living creature in the 30-ft. cone becomes panicked unless it succeeds on a Will save; a creature that succeeds on the save is instead shaken for 1 round (partial save). Modeled as panicked for 4 rounds on a failed save, shaken for 1 round on a successful save. The SRD range is 30 ft. - modeled as the closest category (close)."
 }

src/pf1e_simulator/combat.py

@@ -6010,23 +6010,44 @@ class CombatEngine:
         spell_name: str,
     ) -> str:
         if saved and effect.save_negates:
+            # PF1e partial save (SRD spells/fear.md): a successful save does
+            # not always spare the target — it may impose a weaker condition
+            # (Fear: shaken for 1 round instead of panicked).
+            if effect.save_partial is not None:
+                name, duration = effect.save_partial
+                applied = self._impose_condition(target, name, duration, spell_name)
+                if not applied:
+                    return ""
+                return f"{name} ({duration}r) (partial save)"
             return f"{effect.condition_name} negated"
-        cond = CONDITIONS_BY_NAME.get(effect.condition_name)
+        return self._impose_condition(
+            target, effect.condition_name, effect.duration_rounds, spell_name
+        )
+
+    def _impose_condition(
+        self,
+        target: CombatantState,
+        condition_name: str,
+        duration_rounds: int,
+        spell_name: str,
+    ) -> str:
+        """Append a timed condition to the target; handle the bleeding DoT."""
+        cond = CONDITIONS_BY_NAME.get(condition_name)
         if cond is None:
             return ""
         target.active_conditions.append(
             ActiveCondition(
                 condition=cond,
-                rounds_left=effect.duration_rounds,
+                rounds_left=duration_rounds,
                 source=f"spell: {spell_name}",
             )
         )
-        if effect.condition_name == "bleeding":
+        if condition_name == "bleeding":
             # The bleeding condition's damage-over-time is engine-driven
             # (CombatantState.bleed_damage, CRB Conditions — bleeding); the
             # SRD Bleed cantrip (spells/bleed.md) deals 1 bleed damage/round.
             target.bleed_damage = max(target.bleed_damage, 1)
-        return f"{effect.condition_name} ({effect.duration_rounds}r)"
+        return f"{condition_name} ({duration_rounds}r)"
 
     def _apply_heal_effect(
         self,
@@ -6222,10 +6243,14 @@ class CombatEngine:
             return effect
         if isinstance(effect, ConditionEffect):
             duration = effect.duration_rounds * 2 if has_extend else effect.duration_rounds
+            partial = effect.save_partial
+            if partial is not None and has_extend:
+                partial = (partial[0], partial[1] * 2)
             return ConditionEffect(
                 condition_name=effect.condition_name,
                 duration_rounds=duration,
                 save_negates=effect.save_negates,
+                save_partial=partial,
             )
         if isinstance(effect, BuffEffect):
             duration = effect.duration_rounds * 2 if has_extend else effect.duration_rounds

src/pf1e_simulator/spells.py

@@ -173,6 +173,10 @@ class ConditionEffect:
     condition_name: str
     duration_rounds: int
     save_negates: bool = True
+    # PF1e partial save (SRD spells/fear.md): on a SUCCESSFUL save the target
+    # is not spared outright but suffers a weaker condition instead. Encoded as
+    # (condition_name, duration_rounds); None = a successful save fully negates.
+    save_partial: tuple[str, int] | None = None
 
 
 @dataclass(frozen=True)
@@ -468,6 +472,15 @@ def _parse_recurring(value: Json) -> RecurringDamageSpec:
     )
 
 
+def _parse_save_partial(value: Json) -> tuple[str, int]:
+    data = _as_dict(value)
+    duration = _as_int(data["duration_rounds"])
+    if duration < 1:
+        msg = f"on_success duration_rounds must be >= 1, got {duration}"
+        raise ValueError(msg)
+    return (_as_str(data["condition_name"]), duration)
+
+
 def _parse_effect(data: Json) -> SpellEffect:
     effect = _as_dict(data)
     effect_type = _as_str(effect["type"])
@@ -502,10 +515,13 @@ def _parse_effect(data: Json) -> SpellEffect:
             recurring=recurring,
         )
     if effect_type == "condition":
+        partial_raw = effect.get("on_success")
+        save_partial = None if partial_raw is None else _parse_save_partial(partial_raw)
         return ConditionEffect(
             condition_name=_as_str(effect["condition_name"]),
             duration_rounds=_as_int(effect["duration_rounds"]),
             save_negates=bool(effect.get("save_negates", True)),
+            save_partial=save_partial,
         )
     if effect_type == "heal":
         return HealEffect(

tests/test_spells.py

@@ -172,6 +172,18 @@ class TestSpellLoading:
         assert isinstance(eff, ConditionEffect)
         assert eff.condition_name == "paralyzed"
         assert eff.save_negates is True
+        assert eff.save_partial is None
+
+    def test_fear_condition_has_save_partial(self) -> None:
+        # PF1e (SRD spells/fear.md): a successful Will save imposes shaken 1
+        # round instead of panicked — the partial-save spec.
+        spell = load_spell(_SPELLS_DIR / "fear.json")
+        area = spell.effects[0]
+        assert isinstance(area, AreaEffect)
+        eff = area.effects[0]
+        assert isinstance(eff, ConditionEffect)
+        assert eff.condition_name == "panicked"
+        assert eff.save_partial == ("shaken", 1)
 
     def test_cure_light_has_heal_effect(self) -> None:
         spell = load_spell(_SPELLS_DIR / "cure_light_wounds.json")
@@ -534,9 +546,9 @@ class TestHoldPerson:
 
 class TestFear:
     """Given: a caster casting Fear (SRD spells/fear.md: panicked unless the
-    Will save succeeds)
-    When: target fails save
-    Then: panicked condition is applied."""
+    Will save succeeds; a successful save makes the creature shaken 1 round)
+    When: target fails / succeeds the save
+    Then: panicked is applied / shaken (partial save) is applied instead."""
 
     def test_failed_save_applies_panicked(self) -> None:
         caster = _make_caster()
@@ -544,6 +556,20 @@ class TestFear:
         engine, c, t = _make_engine(caster, target, [2])
         engine._cast_spell(c, t, "Fear")
         assert any(ac.condition.name == "panicked" for ac in t.active_conditions)
+        assert not any(ac.condition.name == "shaken" for ac in t.active_conditions)
+
+    def test_successful_save_applies_shaken(self) -> None:
+        """Given: the target succeeds its Will save (natural 20)
+        When: Fear resolves
+        Then: it is shaken for 1 round (partial save), not panicked."""
+        caster = _make_caster()
+        target = _make_target()
+        engine, c, t = _make_engine(caster, target, [20])
+        engine._cast_spell(c, t, "Fear")
+        shaken = [ac for ac in t.active_conditions if ac.condition.name == "shaken"]
+        assert len(shaken) == 1
+        assert shaken[0].rounds_left == 1
+        assert not any(ac.condition.name == "panicked" for ac in t.active_conditions)
 
 
 class TestCureLightWounds: