fix(rules): knock prone only on a 5-point overrun margin

PF1e CRB 'Overrun': 'If your maneuver is successful, you move through
the target's space. If your attack exceeds your opponent's CMD by 5 or
more, ... the target is knocked prone.' The engine knocked the target
prone on ANY success. A plain success (margin 0-4) now only moves the
attacker through; prone requires total - CMD >= 5 (_OVERRUN_PRONE_MARGIN).

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

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

README.md

@@ -955,8 +955,12 @@ Règles modélisées :
   sans boucle multi-tour. Un sunder endommage l'**arme**, pas les PV : `str_mod + 2`
   de dégâts à l'arme, qui se brise à 10 d'usure cumulée (`_WEAPON_DURABILITY`) →
   `disarmed` ; une arme brisée est exclue de `usable_attacks()` et réparable via
-  `Action(kind="repair_weapon")`. overrun →
-  `prone` 1 round + passage au travers si la case au-delà est libre ; dirty trick →
+   `Action(kind="repair_weapon")`. overrun →
+   passage au travers si la case au-delà est libre, et `prone` 1 round
+   **seulement si le jet dépasse le CMD de 5 ou plus** (conformance R3 — CRB
+   « Overrun » : « If your attack exceeds your opponent's CMD by 5 or more,
+   you move through the target's space and the target is knocked prone ») ;
+   un succès par 0–4 points ne fait que traverser, sans renverser ; dirty trick →
   condition choisie par `Action.trick_condition` (défaut `dazzled` 1 round ;
   `blinded`/`deafened`/`entangled`/`nauseated` possibles) ; steal → l'arme de
   mêlée de la cible est volée (exclue de `usable_attacks()`, récupérable via

src/pf1e_simulator/combat.py

@@ -246,6 +246,7 @@ _PRECISION_IMMUNE_TYPES: frozenset[str] = frozenset({"undead", "construct"})
 _AID_ANOTHER_DC = 10  # PF1e: aid another is an attack roll against AC 10
 _AID_ANOTHER_BONUS = 2  # PF1e: a successful aid grants +2 (next attack or AC)
 _RUN_SPEED_FACTOR = 4  # PF1e: running is a full-round action at 4x speed
+_OVERRUN_PRONE_MARGIN = 5  # PF1e: overrun knocks prone only on a 5+ CMB margin
 _SAVE_DESCRIPTOR_CONDITIONS = frozenset({
     "fear", "cold", "electricity", "fey", "divination", "poison", "disease",
     "mind_affecting",
@@ -4077,19 +4078,28 @@ class CombatEngine:
         if not m.success:
             self._maneuver_fail(state, target, "overrun", m)
             return
-        target.active_conditions.append(
-            ActiveCondition(
-                condition=CONDITIONS_BY_NAME["prone"],
-                rounds_left=1,
-                source="maneuver: overrun",
+        # PF1e (CRB "Overrun"): a successful maneuver moves you through the
+        # target's square; the target is knocked prone only if the attack
+        # exceeds its CMD by 5 or more.
+        knocked_prone = m.total - m.target_cmd >= _OVERRUN_PRONE_MARGIN
+        if knocked_prone:
+            target.active_conditions.append(
+                ActiveCondition(
+                    condition=CONDITIONS_BY_NAME["prone"],
+                    rounds_left=1,
+                    source="maneuver: overrun",
+                )
             )
-        )
         beyond = self._beyond_cell(state.pos, target.pos)
-        if self._cells_free(self._footprint_at(beyond, state), state):
+        moved_through = self._cells_free(self._footprint_at(beyond, state), state)
+        if moved_through:
             state.pos = beyond
-            outcome = "SUCCESS (prone, moved through)"
-        else:
-            outcome = "SUCCESS (prone)"
+        achieved = ", ".join(
+            label
+            for label, flag in (("prone", knocked_prone), ("moved through", moved_through))
+            if flag
+        )
+        outcome = f"SUCCESS ({achieved})" if achieved else "SUCCESS"
         self._log(
             f"round {self._current_round} {state.combatant.id}: overrun vs "
             f"{target.combatant.id} d20={m.roll}+{m.attacker_cmb}={m.total} "

tests/test_maneuvers.py

@@ -123,11 +123,13 @@ def test_escape_from_grapple_consumes_single_d20() -> None:
 
 
 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).
     a_spec = make_combatant("a", attack_bonus=2)
     b_spec = make_combatant("b")
     a = make_state(a_spec, "players", (1, 1))
     b = make_state(b_spec, "monsters", (1, 2))
-    engine = make_engine([1, 12], [a, b])
+    engine = make_engine([1, 15], [a, b])
     engine._execute_maneuver(a, b, "overrun")
     prone = next(c for c in b.active_conditions if c.condition.name == "prone")
     assert prone.rounds_left == 1
@@ -135,14 +137,31 @@ def test_overrun_knocks_prone_and_moves_through() -> None:
     assert a.pos == (1, 3)
 
 
+def test_overrun_small_margin_moves_through_without_prone() -> None:
+    # d20=14+2=16 vs CMD 12: margin 4 -> plain success: moved through,
+    # NOT prone (CRB "Overrun").
+    a_spec = make_combatant("a", attack_bonus=2)
+    b_spec = make_combatant("b")
+    a = make_state(a_spec, "players", (1, 1))
+    b = make_state(b_spec, "monsters", (1, 2))
+    engine = make_engine([1, 14], [a, b])
+    engine._execute_maneuver(a, b, "overrun")
+    assert not any(c.condition.name == "prone" for c in b.active_conditions)
+    assert a.pos == (1, 3)
+    assert "SUCCESS (moved through)" in engine._transcript[-1]
+    assert "prone" not in engine._transcript[-1]
+
+
 def test_overrun_prone_but_no_space() -> None:
+    # d20=15+2=17 vs CMD 12: margin 5 -> prone; the beyond cell is occupied,
+    # so no move-through.
     a_spec = make_combatant("a", attack_bonus=2)
     b_spec = make_combatant("b")
     c_spec = make_combatant("c")
     a = make_state(a_spec, "players", (1, 1))
     b = make_state(b_spec, "monsters", (1, 2))
     c = make_state(c_spec, "monsters", (1, 3))
-    engine = make_engine([1, 12], [a, b, c])
+    engine = make_engine([1, 15], [a, b, c])
     engine._execute_maneuver(a, b, "overrun")
     assert any(cond.condition.name == "prone" for cond in b.active_conditions)
     assert a.pos == (1, 1)