fix(rules): stop damage reduction from eating energy damage

PF1e (CRB Damage Reduction): "Damage reduction does not negate ...
energy damage dealt along with an attack." _resolve_hit_damage now
splits the post-crit total and applies DR only to the non-energy share
(physical dice + flat bonuses + precision dice); energy components are
reduced solely by the per-component energy resistance/immunity step.
DR-bypass semantics (multi-component "and" requires every component)
are unchanged. Pure-physical weapons keep bit-identical arithmetic and
the golden transcripts are untouched.

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

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

README.md

@@ -831,8 +831,14 @@ Règles modélisées :
   1d6 tranchant + 1d6 feu contre résistance feu 5 ne perd que ses dés de feu, les
   dés tranchants, les bonus plats et les dés de précision (attaque sournoise, non
   typés) restent intacts ; l'immunité à un type annule uniquement les composantes
-  de ce type. Les types physiques (contondant/perforant/tranchant) restent sur le
+   de ce type. Les types physiques (contondant/perforant/tranchant) restent sur le
-  chemin de la RD, appliquée au total comme avant. La résistance énergétique
+   chemin de la RD, appliquée **uniquement à la part physique** du dégât (dés
+   physiques + bonus plats + précision) — conformance A3 (CRB « Damage
+   Reduction » : « Damage reduction does not negate … energy damage dealt along
+   with an attack ») : la RD ne mange plus la composante énergétique d'une
+   attaque mixée (ex. arme à feu infligeant des dégâts de feu contre RD 15) ;
+   les composantes énergétiques ne sont réduites que par résistance/immunité
+   énergétique. La résistance énergétique
   s'applique à l'étape du dégât final (même étape que la RD), y compris aux dégâts
   de sorts (un `DamageEffect` est une composante unique — comportement inchangé).
 - Concealment (chance de rater) : les conditions `blurred` (20 %, sort flou),

src/pf1e_simulator/combat.py

@@ -36,7 +36,10 @@ Phase 0 documented deviations from PF1e (conventions):
   natural weapons in a single full attack are not modeled.
 - Natural 1 always misses; natural 20 always hits and threatens a crit.
 - A confirmed crit multiplies the total damage (dice + flat bonus) by crit_mult.
-- DR applies once, after crit multiplication; a single bypass type defeats
+- DR applies once, after crit multiplication, to the PHYSICAL portion of the
+  damage only (bludgeoning/piercing/slashing dice, flat bonuses and precision
+  dice) — energy damage dealt along with an attack is never reduced by DR
+  (CRB "Damage Reduction"); a single bypass type defeats
   DR; a multi-component "and" bypass (e.g. "bludgeoning and magic") requires
   EVERY component (PF1e "DR X/Y and Z" notation).
 - Death when negative hp reaches the Constitution score (hp <= -CON); PF1e
@@ -182,6 +185,9 @@ _FIGHT_DEFENSIVELY_AC_BONUS = 2  # PF1e: fighting defensively grants +2 dodge AC
 _FIGHT_DEFENSIVELY_ATTACK_PENALTY = -4  # PF1e: and -4 on attacks / crit confirms
 _SPELL_COMBAT_ATTACK_PENALTY = -2  # PF1e: magus Spell Combat melee attacks at -2
 _TOTAL_CONCEALMENT_PCT = 50  # PF1e: a blinded attacker's targets have total concealment
+# PF1e (CRB Damage Reduction): DR does not negate energy damage dealt along
+# with an attack — only these weapon damage types ride the DR path.
+_PHYSICAL_DAMAGE_TYPES = frozenset({"bludgeoning", "piercing", "slashing"})
 # PF1e confused d% table: 01-25 act normally, 26-50 babble, 51-75 hit self,
 # 76-100 attack the nearest creature
 _CONFUSED_ACT_NORMAL_MAX = 25
@@ -2442,7 +2448,19 @@ class CombatEngine:
         if crit:
             damage *= weapon.crit_mult
         damage += sneak_total
-        damage = self._apply_dr(damage, weapon, target)
+        # PF1e (CRB Damage Reduction): "Damage reduction does not negate ...
+        # energy damage dealt along with an attack" — DR reduces only the
+        # non-energy share of the damage (physical dice, flat bonuses and
+        # precision dice); energy components are cut solely by energy
+        # resistance/immunity in the per-component step below.
+        mult = weapon.crit_mult if crit else 1
+        energy_share = sum(
+            roll * mult
+            for comp, roll in zip(weapon.damage, rolls, strict=True)
+            if not _PHYSICAL_DAMAGE_TYPES.issuperset(comp.types)
+        )
+        physical = max(0, damage - energy_share)
+        damage = self._apply_dr(physical, weapon, target) + energy_share
         return crit, False, self._apply_energy_resistance_per_component(
             damage, weapon, rolls, crit=crit, target=target
         )
@@ -2633,10 +2651,11 @@ class CombatEngine:
         A component carrying several energy types uses the largest matching
         resistance (documented simplification: one die roll cannot be split
         across the listed types). Physical-only components match nothing in
-        the target's resistance/immunity maps and stay on the DR path, which
+        the target's resistance/immunity maps — they rode the DR path just
-        was applied to the lumped total just before this step (unchanged);
+        before this step, which reduces only the non-energy share of the
-        single-component weapons keep the exact arithmetic of the old
+        damage (CRB: DR does not negate energy damage dealt along with an
-        lumped-total path.
+        attack); single-component weapons keep the exact arithmetic of the
+        old lumped-total path.
         """
         mult = weapon.crit_mult if crit else 1
         for comp, roll in zip(weapon.damage, rolls, strict=True):

tests/test_conformance_energy.py

@@ -19,6 +19,7 @@ from pf1e_simulator.models import (
     AttackSpec,
     Combatant,
     DamageComponent,
+    DamageReduction,
     Saves,
 )
 from pf1e_simulator.rng import ScriptedRng
@@ -206,3 +207,39 @@ def test_sneak_precision_not_reduced_by_energy_resistance() -> None:
     # the 6 precision dice survive intact (the old lumped path dealt 0).
     assert result.damage == 6
     assert eng._states[2].hp == 94
+
+
+def test_dr_spares_the_energy_component_of_a_mixed_attack() -> None:
+    """(g) A3: DR reduces only the physical share — energy dice pass through.
+
+    PF1e (CRB "Damage Reduction"): "Damage reduction does not negate ...
+    energy damage dealt along with an attack." 1d8 piercing = 3 + 1d6 fire = 6
+    against DR 5: the old lumped path dealt max(0, 9-5) = 4 (DR ate 2 of the
+    fire dice); the fix reduces only the 3 piercing damage (floored at 0) and
+    the full 6 fire damage lands.
+    """
+    weapon = _attack(
+        "flintlock",
+        (("1d8", ("piercing",)), ("1d6", ("fire",))),
+    )
+    hero = _combatant("hero", attacks=(weapon,))
+    foe = _combatant("foe")
+    foe = foe.model_copy(update={"dr": DamageReduction(amount=5)})
+    eng = _engine([hero, foe], [(0, 0), (0, 1)], ["players", "monsters"],
+                  [15, 3, 6])
+    result = eng.resolve_attack(eng._states[0], eng._states[1], weapon)
+    assert result.damage == 6
+    assert eng._states[1].hp == 94
+
+
+def test_physical_only_damage_vs_dr_unchanged() -> None:
+    """(h) a physical-only weapon keeps the exact old DR arithmetic (regression
+    lock for the split): 1d8 = 3 vs DR 5 floors to 0."""
+    weapon = _attack("warhammer", (("1d8", ("bludgeoning",)),))
+    hero = _combatant("hero", attacks=(weapon,))
+    foe = _combatant("foe").model_copy(update={"dr": DamageReduction(amount=5)})
+    eng = _engine([hero, foe], [(0, 0), (0, 1)], ["players", "monsters"],
+                  [15, 3])
+    result = eng.resolve_attack(eng._states[0], eng._states[1], weapon)
+    assert result.damage == 0
+    assert eng._states[1].hp == 100