fix(combat): Thread 5-10-5 diagonal parity through all budget-consuming paths

The greedy move/run/flee/charge descent helpers hardcoded diagonal parity 0,
letting a speed-30 walker cover 6 diagonal cells (cell-count budget). Under
5-10-5 (SRD Movement, Tactical) the same walker covers only 4 cells
(1+2+1+2=6 squares).

Threading the running diagonal count:
- _best_move_step / _best_flee_step: accept diagonals_used param
- _descend_path / _run_line_path / _flee_path: track and pass parity
- _charge_end: use _path_cost_5105() instead of len(path) for max check
- _path_cost_5105: new helper; computes total 5-10-5 cost of any path

Updated golden paths in test_aoo_limit_one_per_round (5-cell path now
takes an orthogonal detour to avoid expensive 2nd diagonal), test_run_*
 (speed-30 diagonal move stops at 4 cells), and staggered_withdraw
(single-speed diagonal withdraw stops at 4 cells).

src/pf1e_simulator/combat.py

@@ -118,6 +118,7 @@ from __future__ import annotations
 
 from collections.abc import Callable, Iterable
 from dataclasses import asdict, dataclass, field
+from itertools import pairwise
 from pathlib import Path
 from typing import TYPE_CHECKING, Literal
 
@@ -3643,6 +3644,16 @@ class CombatEngine:
                 return ChargeResult(weapon=weapon, distance_ft=distance_ft, reason=None)
         return ChargeResult(weapon=None, distance_ft=0, reason="no_charge_path")
 
+    def _path_cost_5105(self, path: list[Pos]) -> int:
+        """Total 5-10-5 movement cost of a path (diagonal parity threaded)."""
+        total = 0
+        diagonals_used = 0
+        for frm, to in pairwise(path):
+            total += self._grid.step_cost(frm, to, diagonals_used)
+            if frm[0] != to[0] and frm[1] != to[1]:
+                diagonals_used += 1
+        return total
+
     def _charge_end(
         self,
         state: CombatantState,
@@ -3675,10 +3686,14 @@ class CombatEngine:
             if dist > reach_cells or dist < min_reach_cells:
                 continue
             path = _bresenham_line(state.pos, end)
-            if len(path) < _CHARGE_MIN_CELLS or len(path) > max_cells:
+            if len(path) < _CHARGE_MIN_CELLS:
                 continue
             if not self._charge_path_clear(path, state):
                 continue
+            # The charge budget is a movement budget: count it in 5-10-5
+            # squares (diagonal parity threaded), not raw cells.
+            if self._path_cost_5105(path) > max_cells:
+                continue
             candidates.append((len(path), end))
         if not candidates:
             return None
@@ -7071,14 +7086,20 @@ class CombatEngine:
         path: list[Pos] = []
         current = state.pos
         budget = speed_cells
+        diagonals_used = 0
         while budget > 0:
             best = self._best_move_step(
-                state, current, to_target, budget,
+                state, current, to_target, budget, diagonals_used,
                 avoid_difficult=avoid_difficult, friendly_passable=friendly_passable,
             )
             if best is None:
                 break
             _, step_cost, nxt = best
+            # PF1e 5-10-5: the diagonal cost alternates 1-2-1-2, so the
+            # running diagonal count must follow the walk (grid.reachable
+            # already tracks it; the greedy descent must too).
+            if current[0] != nxt[0] and current[1] != nxt[1]:
+                diagonals_used += 1
             current = nxt
             path.append(current)
             budget -= step_cost
@@ -7111,16 +7132,19 @@ class CombatEngine:
             return []
         path: list[Pos] = []
         current = state.pos
+        diagonals_used = 0
         for nxt in _bresenham_line(state.pos, goal):
             footprint = self._footprint_at(nxt, state)
             if self._footprint_touches_difficult(footprint):
                 break
             if not self._cells_walkable(footprint, state):
                 break
-            step = self._grid.step_cost(current, nxt, 0)
+            step = self._grid.step_cost(current, nxt, diagonals_used)
             if step > budget:
                 break
             path.append(nxt)
+            if current[0] != nxt[0] and current[1] != nxt[1]:
+                diagonals_used += 1
             current = nxt
             budget -= step
         while path and not self._cells_free(self._footprint_at(path[-1], state), state):
@@ -7133,6 +7157,7 @@ class CombatEngine:
         current: Pos,
         to_target: dict[Pos, int],
         budget: int,
+        diagonals_used: int,
         *,
         avoid_difficult: bool = False,
         friendly_passable: bool = False,
@@ -7169,7 +7194,7 @@ class CombatEngine:
                 and not self._has_free_descent(state, nxt, to_target, nxt_cost)
             ):
                 continue
-            step = self._grid.step_cost(current, nxt, 0)
+            step = self._grid.step_cost(current, nxt, diagonals_used)
             if step > budget:
                 continue
             score = step + nxt_cost
@@ -7230,11 +7255,16 @@ class CombatEngine:
         path: list[Pos] = []
         current = state.pos
         budget = max_cells
+        diagonals_used = 0
         while budget > 0:
-            best = self._best_flee_step(state, current, from_threat, budget)
+            best = self._best_flee_step(
+                state, current, from_threat, budget, diagonals_used
+            )
             if best is None:
                 break
             _, step_cost, nxt = best
+            if current[0] != nxt[0] and current[1] != nxt[1]:
+                diagonals_used += 1
             current = nxt
             path.append(current)
             budget -= step_cost
@@ -7246,6 +7276,7 @@ class CombatEngine:
         current: Pos,
         from_threat: dict[Pos, int],
         budget: int,
+        diagonals_used: int,
     ) -> tuple[int, int, Pos] | None:
         """Pick the adjacent anchor that maximizes distance from the threat."""
         current_cost = self._footprint_cost(self._footprint_at(current, state), from_threat)
@@ -7263,7 +7294,7 @@ class CombatEngine:
             nxt_cost = self._footprint_cost(footprint, from_threat)
             if nxt_cost is None or nxt_cost <= current_cost:
                 continue
-            step = self._grid.step_cost(current, nxt, 0)
+            step = self._grid.step_cost(current, nxt, diagonals_used)
             if step > budget:
                 continue
             score = -(nxt_cost * 100) + step

tests/test_aid_and_run.py

@@ -358,7 +358,9 @@ def test_run_toward_target_outreaches_normal_move() -> None:
     )
     eng2.run()
     move_hero = eng2._states[0]
-    assert move_hero.pos == (6, 6)  # only 6 cells of the 15-cell path
+    # 5-10-5: 4 diagonal cells cost 1+2+1+2 = 6 = the speed budget; the old
+    # cell-count budget let a speed-30 walker cover 6 diagonal cells.
+    assert move_hero.pos == (4, 4)  # only 4 diagonal cells of the 15-cell path
     assert grid.distance(run_hero.pos, foe.pos) < grid.distance(move_hero.pos, foe2.pos)
 
 

tests/test_combat.py

@@ -1071,7 +1071,10 @@ def test_aoo_limit_one_per_round() -> None:
         "initiative: guard d20=9+0=9",
         "initiative: dest d20=8+0=8",
         "round 1 guard: AoO vs runner d20=15+5=20 AC 12 -> HIT 3 damage (20->17)",
-        "round 1 runner: move (0,0)->(0,1)->(1,2)->(2,3)->(3,3)",
+        # 5-10-5 parity: the second diagonal (1,2)->(2,3) now costs 2, so the
+        # greedy walk prefers the orthogonal (1,2)->(1,3) detour (both paths
+        # total 5 squares; the new one avoids the expensive second diagonal).
+        "round 1 runner: move (0,0)->(0,1)->(1,2)->(1,3)->(2,3)->(3,3)",
         "round 1 guard: wait",
         "round 1 dest: wait",
         "battle over: draw after 1 rounds",

tests/test_conditions_effects.py

@@ -220,8 +220,9 @@ class TestStaggeredActionEconomy:
             line for line in engine._transcript if "withdraw" in line
         ]
         assert len(withdraw_lines) == 1
-        # 6 steps from (10,10) — exactly the single-speed budget.
+        # 4 diagonal steps from (10,10) — the single-speed budget of 6 squares
-        assert withdraw_lines[0].count("->") == 6
+        # under 5-10-5 (1+2+1+2=6); the old cell-count budget let it walk 6.
+        assert withdraw_lines[0].count("->") == 4
         assert h.pos != (10, 10)