Sight travels through the wraparound openings

"If casting a spell, or checking line of sight through the AUTO WARP,
treat it as a straight line, and the two connected boards as though
they were adjacent" — and the lettered openings reconnect edges the
same way. hasWarpLineOfSight models it: the line must run straight
down the corridor, out one mouth, and in through the paired mouth,
with both corridor legs clear and neither mouth filled solid. The new
sightBetween (direct or through-a-warp) is now the game's LOS check
everywhere — spells, ambush triggers, Around The Corner, the
visionstone sweep, and the targeting dim on the client.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

packages/engine/test/board.test.ts

@@ -3,6 +3,7 @@ import {
   assembleBoard,
   edgeState,
   hasLineOfSight,
+  sightBetween,
   layoutIds,
   stepTarget,
   type SectorPlacement,
@@ -136,3 +137,39 @@ describe("player counts 2-6", () => {
     }
   });
 });
+
+describe("line of sight through wraparound openings", () => {
+  const twoSector: SectorPlacement[] = [
+    { boardId: "board-a", origin: { x: 0, y: 0 }, rotation: 0 },
+    { boardId: "board-b", origin: { x: 0, y: 5 }, rotation: 0 },
+  ];
+
+  it("sees straight down the corridor, out one mouth and in the other", () => {
+    const board = assembleBoard(twoSector);
+    // (2,0) N wraps to (2,9): the mouths see each other through the join.
+    expect(hasLineOfSight(board, { x: 2, y: 0 }, { x: 2, y: 9 })).toBe(false);
+    expect(sightBetween(board, { x: 2, y: 0 }, { x: 2, y: 9 })).toBe(true);
+    expect(sightBetween(board, { x: 2, y: 9 }, { x: 2, y: 0 })).toBe(true);
+  });
+
+  it("demands a straight corridor: off-axis viewers see nothing", () => {
+    const board = assembleBoard(twoSector);
+    expect(sightBetween(board, { x: 1, y: 0 }, { x: 2, y: 9 })).toBe(false);
+    expect(sightBetween(board, { x: 3, y: 1 }, { x: 2, y: 9 })).toBe(false);
+  });
+
+  it("walls inside either corridor still block the warp sight", () => {
+    const board = assembleBoard(twoSector);
+    // Layout A: the wall between (2,0) and (2,1)'s row (home column sight is
+    // cut above row 2 — pinned earlier) blocks a deeper viewer's warp sight.
+    const deepViewer = { x: 2, y: 2 };
+    expect(hasLineOfSight(board, deepViewer, { x: 2, y: 0 })).toBe(false);
+    expect(sightBetween(board, deepViewer, { x: 2, y: 9 })).toBe(false);
+  });
+
+  it("a filled mouth chokes the tunnel", () => {
+    const board = assembleBoard(twoSector);
+    const stone = { "2,9": true as const };
+    expect(sightBetween(board, { x: 2, y: 0 }, { x: 2, y: 8 }, stone)).toBe(false);
+  });
+});