fix(rules): combat maneuvers auto-succeed (natural 20) vs incapacitated targets

src/pf1e_simulator/combat.py

@@ -4641,6 +4641,15 @@ class CombatEngine:
         attacker_cmb = self._maneuver_cmb(state) - pa_amt - grapple_penalty
         target_cmd = self._maneuver_cmd(target)
         roll = self._rng.d20()
+        # PF1e (SRD Combat Maneuvers): "If your target is immobilized,
+        # unconscious, or otherwise incapacitated, your maneuver
+        # automatically succeeds (treat as if you rolled a natural 20 on
+        # the attack roll)." The engine's incapacitated notion is the
+        # helpless set (helpless/paralyzed/asleep/unconscious, CRB
+        # "Conditions"); the natural 20 also feeds the margin-based
+        # outcomes (bull rush / overrun / reposition / drag / dirty trick).
+        if self._is_helpless(target):
+            roll = _NATURAL_TWENTY
         # PF1e (CRB Combat Maneuvers): the provoked-AoO damage rides the
         # check total (floored at 0); natural 20/1 keep their rules below.
         total = max(0, roll + attacker_cmb - aoo_damage)

tests/test_maneuvers.py

@@ -340,6 +340,44 @@ def test_disarm_fail_by_10_drops_attacker_weapon() -> None:
     assert any("disarm backfire -> drops sword" in line for line in engine._transcript)
 
 
+# --- SRD Combat Maneuvers: auto-success against an incapacitated target -------
+
+
+def test_maneuver_auto_succeeds_vs_helpless_target() -> None:
+    # SRD Combat Maneuvers: "If your target is immobilized, unconscious, or
+    # otherwise incapacitated, your maneuver automatically succeeds (treat
+    # as if you rolled a natural 20 on the attack roll)." b (bab 20) has CMD
+    # 30: a natural 1 would normally auto-fail, but the helpless target
+    # forces the natural-20 treatment -> trip succeeds.
+    a = make_state(make_combatant("a", attack_bonus=2), "players", (1, 1))
+    b = make_state(make_combatant("b", attack_bonus=20), "monsters", (1, 2))
+    _conditioned(b, "paralyzed")
+    engine = make_engine([1, 1], [a, b])
+    engine._execute_maneuver(a, b, "trip")
+    assert any(c.condition.name == "prone" for c in b.active_conditions)
+    assert "d20=20" in engine._transcript[-1]
+
+
+def test_maneuver_auto_succeeds_vs_asleep_target_with_margin() -> None:
+    # The natural-20 treatment feeds the margin outcomes: a CMB 2 vs CMD 12,
+    # roll forced to 20 -> total 22, margin 10 -> bull rush pushes 3 cells.
+    a = make_state(make_combatant("a", attack_bonus=2), "players", (1, 1))
+    b = make_state(make_combatant("b"), "monsters", (1, 2))
+    _conditioned(b, "asleep")
+    engine = make_engine([1, 5], [a, b])
+    engine._execute_maneuver(a, b, "bull_rush")
+    assert b.pos == (1, 5)
+
+
+def test_maneuver_normal_roll_still_fails_vs_awake_target() -> None:
+    # Control: the same natural 1 against a non-helpless target auto-fails.
+    a = make_state(make_combatant("a", attack_bonus=2), "players", (1, 1))
+    b = make_state(make_combatant("b"), "monsters", (1, 2))
+    engine = make_engine([1, 1], [a, b])
+    engine._execute_maneuver(a, b, "trip")
+    assert not any(c.condition.name == "prone" for c in b.active_conditions)
+
+
 def test_overrun_knocks_prone_and_moves_through() -> None:
     # d20=15+2=17 vs CMD 12: margin 5 -> prone AND moved through (CRB
     # "Overrun": prone only when the attack exceeds CMD by 5 or more).