fix(rules): cones require line of effect from their origin (SRD aiming-a-spell.md: a cone 'affects only an area, creature, or object to which it has line of effect from its origin') - cone_cells drops geometrically-inside cells without corner-to-corner LoE from the caster square; line/cone barrier-cell semantics aligned (both templates include the barrier square the effect strikes, exclude everything behind it)

src/pf1e_simulator/areas.py

@@ -18,8 +18,15 @@ PF1e (CRB, Magic — Aiming a Spell):
   fill it). The line also stops at the first square that blocks line of
   effect (CRB, Magic - Aiming a Spell, Line: it "extends to the limit of its
   range or until it strikes a barrier that blocks line of effect"): the
-  barrier square itself and everything beyond it are outside the template,
-  so a bolt never reaches creatures behind a solid wall.
+  barrier square is the last square of the template and everything beyond
+  it is outside, so a bolt never reaches creatures behind a solid wall.
+- Cones require line of effect from their origin (CRB, Magic - Line of
+  Effect): "A burst, cone, cylinder, or emanation spell affects only an
+  area, creature, or object to which it has line of effect from its origin
+  (a spherical burst's center point, a cone-shaped burst's starting
+  point, ...)". ``cone_cells`` therefore drops every geometric cell that
+  has no corner-to-corner line of effect from the origin square (a solid
+  wall between them shields everything behind it).
 
 Bursts need no template here: they are circles around a center cell and are
 resolved by ``CombatEngine._creatures_in_range`` (unchanged).
@@ -29,6 +36,8 @@ from __future__ import annotations
 
 from typing import TYPE_CHECKING
 
+from pf1e_simulator.los import has_line_of_effect
+
 if TYPE_CHECKING:
     from pf1e_simulator.grid import Grid
     from pf1e_simulator.map import Pos
@@ -44,7 +53,11 @@ def cone_cells(
     from the origin is within ``radius_cells`` (5-10-5 grid distance), points
     strictly into the cone's forward half-plane, and stays within ±45° of the
     aim bearing. The origin cell itself is never affected (CRB: the cone
-    "shoots away from you"). A degenerate aim (origin == aim) affects nothing.
+    "shoots away from you"). A cell with no line of effect from the origin
+    is dropped (CRB, Line of Effect: a cone "affects only an area, creature,
+    or object to which it has line of effect from its origin" - a solid wall
+    stops the cone, it does not pass through). A degenerate aim
+    (origin == aim) affects nothing.
 
     The ±45° test is exact integer arithmetic: with v the cell offset and d
     the aim offset, ``cos(angle) >= cos(45°)`` is equivalent to
@@ -70,6 +83,8 @@ def cone_cells(
                 continue
             if grid.distance(origin, cell) > radius_cells:
                 continue
+            if not has_line_of_effect(grid, origin, cell):
+                continue
             cells.add(cell)
     return frozenset(cells)
 
@@ -87,7 +102,8 @@ def line_cells(
     the ray. Out-of-bounds cells simply drop out of the template (creatures
     only exist in bounds). The ray stops at the first cell that blocks line
     of effect (CRB, Line: "or until it strikes a barrier that blocks line of
-    effect") - that barrier cell and everything beyond it are excluded. A
+    effect") - the barrier cell itself is the last cell of the template (the
+    line strikes it) and everything beyond it is excluded. A
     degenerate aim (origin == aim) affects nothing.
     """
     if length_cells <= 0:
@@ -109,9 +125,9 @@ def line_cells(
     for cell in ray[1 : length_cells + 1]:
         if not grid.in_bounds(cell):
             continue
+        cells.append(cell)
         if grid.terrain_at(cell).blocks_los:
             break
-        cells.append(cell)
     return frozenset(cells)
 
 

tests/test_area_shapes.py

@@ -18,7 +18,7 @@ from typing import TYPE_CHECKING
 
 import pytest
 
-from pf1e_simulator.areas import line_cells
+from pf1e_simulator.areas import cone_cells, line_cells
 from pf1e_simulator.combat import Action, CombatantState, CombatEngine
 from pf1e_simulator.dice import parse_dice
 from pf1e_simulator.grid import Grid
@@ -185,6 +185,48 @@ def test_cone_covers_the_full_90_degree_arc() -> None:
     assert foe_outside.hp == 100
 
 
+def test_cone_cells_require_line_of_effect_from_the_origin() -> None:
+    """Given: a wall column at col 4 (rows 4-8) between origin (6,2) and the
+    cell (6,5) that sits on the cone axis at distance 3
+    When: cone_cells builds a 3-cell east cone
+    Then: (6,5) is dropped - geometrically inside but without line of effect
+    from the origin (CRB, Line of Effect: a cone "affects only an area,
+    creature, or object to which it has line of effect from its origin");
+    on the same geometry without walls it stays in the template."""
+    walls = frozenset({(4, 4), (5, 4), (6, 4), (7, 4), (8, 4)})
+    grid = _walled_grid(walls)
+    cells = cone_cells(grid, (6, 2), (6, 3), 3)
+    assert (6, 3) in cells
+    assert (6, 4) in cells  # the cone reaches the barrier square itself
+    assert (6, 5) not in cells
+    open_cells = cone_cells(_open_grid(), (6, 2), (6, 3), 3)
+    assert (6, 5) in open_cells  # control: nothing else filters it out
+
+
+def test_cone_behind_a_solid_wall_does_not_hit_sheltered_creatures() -> None:
+    """Given: caster (6,2) aiming the 15-ft cone east at foe_front (6,3); a
+    wall column at col 4 (rows 4-8); foe_behind (6,5) sits on the cone axis
+    behind that wall
+    When: the cone resolves
+    Then: only foe_front is caught (one 1d6 consumed after the adjacent
+    foe_front's scripted -4 AoO d20 misses); foe_behind is untouched - the
+    cone stops at the solid barrier, it does not pass through it."""
+    caster = _caster()
+    walls = frozenset({(4, 4), (5, 4), (6, 4), (7, 4), (8, 4)})
+    foe_front = make_state(make_combatant("foe_front", hp=100), "monsters", (6, 3))
+    foe_behind = make_state(make_combatant("foe_behind", hp=100), "monsters", (6, 5))
+    eng = CombatEngine(
+        ScriptedRng([4, 4]), _walled_grid(walls), [caster, foe_front, foe_behind],
+        spell_registry=_REGISTRY,
+    )
+    result = eng._execute(
+        caster, Action(kind="cast_spell", target_id="foe_front", spell_name="Cone Sparks")
+    )
+    assert result.ok
+    assert foe_front.hp == 100 - 4
+    assert foe_behind.hp == 100
+
+
 def test_cone_directed_by_target_pos_point_cast() -> None:
     """Given: the same scene, no target_id — the cone is aimed at an explicit
     cell (6,5) via target_pos (U7b point cast)
@@ -256,7 +298,7 @@ def test_line_cells_stop_at_a_line_of_effect_barrier() -> None:
     grid = _walled_grid(frozenset({(6, 6)}))
     cells = line_cells(grid, (6, 2), (6, 8), 10)
     assert (6, 5) in cells
-    assert (6, 6) not in cells
+    assert (6, 6) in cells  # the bolt strikes the barrier square itself
     assert (6, 7) not in cells
     assert (6, 8) not in cells