fix(rules): minimum damage - a landed hit reduced below 1 by DR/energy resistance deals 1 (CRB Damage - Minimum Damage, nonlethal approximated as normal)

src/pf1e_simulator/combat.py

@@ -180,6 +180,7 @@ _CHARGE_AC_PENALTY = 2  # PF1e: -2 AC until start of next turn after charging
 _CHARGE_MIN_CELLS = 2  # PF1e: charge must move at least 10 ft (2 squares)
 _UP_CLOSE_RANGE_FT = 30  # PF1e: Up Close and Deadly works within 30 ft
 _GRAPPLED_CMB_PENALTY = 2  # PF1e: grappled/pinned -2 on non-grapple/escape CMB
+_MINIMUM_HIT_DAMAGE = 1  # PF1e (CRB "Damage" - Minimum Damage): a hit deals >= 1
 _DISARM_RETALIATION_MARGIN = 10  # PF1e SRD: disarm fails by 10 -> attacker drops
 # PF1e: Point-Blank Shot grants +1/+1 within 30 ft with ranged weapons
 _POINT_BLANK_RANGE_FT = 30
@@ -2981,9 +2982,15 @@ class CombatEngine:
         )
         physical = max(0, damage - energy_share)
         damage = self._apply_dr(physical, weapon, target) + energy_share
-        return crit, False, self._apply_energy_resistance_per_component(
+        final = self._apply_energy_resistance_per_component(
             damage, weapon, rolls, target=target
         )
+        # PF1e (CRB "Damage" — Minimum Damage): "If penalties reduce the
+        # damage result to less than 1, a hit still deals 1 point of
+        # nonlethal damage." The engine has no nonlethal damage track
+        # (documented approximation): the floor is applied as 1 point of
+        # normal damage on a landed hit.
+        return crit, False, max(_MINIMUM_HIT_DAMAGE, final)
 
     def _attack_cover_bonus(
         self, attacker: CombatantState, target: CombatantState, *, ranged: bool

tests/test_combat.py

@@ -200,15 +200,38 @@ def test_dr_reduces_damage() -> None:
     assert b.hp == 4
 
 
-def test_dr_floors_damage_at_zero() -> None:
+def test_dr_floors_hit_at_one_minimum_damage() -> None:
+    # PF1e (CRB "Damage" - Minimum Damage): "If penalties reduce the damage
+    # result to less than 1, a hit still deals 1 point of nonlethal damage"
+    # (no nonlethal track: floored to 1 point of normal damage).
     a_spec = make_combatant("a", attack_bonus=2)
     b_spec = make_combatant("b", dr=DamageReduction(amount=5))
     a = make_state(a_spec, "players", (1, 1))
     b = make_state(b_spec, "monsters", (1, 2))
     engine = make_engine([12, 3], [a, b])
     result = engine.resolve_attack(a, b, a_spec.attacks[0])
-    assert result.damage == 0
+    assert result.hit is True
-    assert b.hp == 6
+    assert result.damage == 1
+    assert b.hp == 5
+
+
+def test_energy_resistance_floors_hit_at_one() -> None:
+    a_spec = make_combatant("a", attack_bonus=2)
+    b_spec = make_combatant("b").model_copy(update={"resistances": {"fire": 10}})
+    fire = AttackSpec(
+        id="a-fire",
+        name="flame blade",
+        kind="melee",
+        attack_bonus=2,
+        damage=[DamageComponent(formula=parse_dice("1d6"), types=["fire"])],
+    )
+    a = make_state(a_spec, "players", (1, 1))
+    b = make_state(b_spec, "monsters", (1, 2))
+    engine = make_engine([12, 5], [a, b])
+    result = engine.resolve_attack(a, b, fire)
+    assert result.hit is True
+    assert result.damage == 1
+    assert b.hp == 5
 
 
 def test_dr_bypass_ignores_reduction() -> None:

tests/test_conformance_energy.py

@@ -251,12 +251,14 @@ def test_dr_spares_the_energy_component_of_a_mixed_attack() -> None:
 
 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."""
+    lock for the split): 1d8 = 3 vs DR 5 reduces below 1 — the CRB "Damage"
+    Minimum Damage floor then leaves a landed hit dealing 1 (nonlethal is not
+    modeled: 1 point of normal damage)."""
     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 result.damage == 1
-    assert eng._states[1].hp == 100
+    assert eng._states[1].hp == 99  # the Minimum Damage floor lands 1 point