Rev 19: breaching the rim opens a new warp across the maze

Destroying a wall on the board's outer edge used to leave a one-sided
hole into nothing. The table's physics prevail: the outer rim wraps,
so the breach goes clean through — the opposite perimeter wall in the
same row or column crumbles too (collapse damage and all), and a new
warp pair opens between the two edges, shimmering at both mouths.
Rev-gated: stored games hold one-sided breaches and replay so. Sector
moves recompute the wraparounds and forget improvised openings, as
the maze's own reshaping always has.

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

packages/engine/src/game.ts

@@ -24,6 +24,7 @@ import {
   sightBetween,
   neighbor,
   stepTarget,
+  opposite,
 } from "./board";
 import {
   buildDeck,
@@ -592,6 +593,7 @@ export type GameEvent =
   | { type: "ambushCancelled"; visibleTo: PlayerId; ambushId: string }
   | { type: "ambushSprung"; owner: PlayerId; victim: PlayerId; via: string; spellCardId: string; trigger: AmbushTrigger }
   | { type: "wallDestroyed"; caster: PlayerId; edge: { cell: Cell; side: Side }; wasDoor: boolean }
+  | { type: "warpOpened"; a: { cell: Cell; side: Side }; b: { cell: Cell; side: Side } }
   | { type: "wallDamaged"; player: PlayerId; edge: { cell: Cell; side: Side }; amount: number; total: number; needed: number; source: string }
   | { type: "doorUnlocked"; player: PlayerId; edge: { cell: Cell; side: Side }; withCardId: string }
   | { type: "doorHeld"; player: PlayerId; edge: { cell: Cell; side: Side } }
@@ -744,6 +746,32 @@ interface DamagePipeline {
   kind: "spell" | "physical";
 }
 
+/** The opposite perimeter edge in the same row or column — where the
+ * maze's default wraparound would connect ("only opposite board edges
+ * connect"). Null when the board's shape offers no counterpart. */
+function oppositePerimeter(
+  board: AssembledBoard, cell: Cell, side: Side,
+): { cell: Cell; side: Side } | null {
+  const along = side === "E" || side === "W" ? "x" : "y";
+  const fixed = along === "x" ? cell.y : cell.x;
+  let best: Cell | null = null;
+  for (const key of Object.keys(board.cells)) {
+    const [x, y] = key.split(",").map(Number) as [number, number];
+    if ((along === "x" ? y : x) !== fixed) continue;
+    const c = { x, y };
+    if (best === null ||
+        (side === "E" || side === "S" ? (along === "x" ? x < best.x : y < best.y)
+                                      : (along === "x" ? x > best.x : y > best.y))) {
+      best = c;
+    }
+  }
+  if (!best || cellKey(best) === cellKey(cell)) return null;
+  const oppSide = opposite(side);
+  // The counterpart must itself be a rim: nothing beyond it.
+  if (board.cells[cellKey(neighbor(best, oppSide))]) return null;
+  return { cell: best, side: oppSide };
+}
+
 /** The far mouth of the warp whose near mouth is this edge, if any. */
 function pairedWarpMouth(
   board: AssembledBoard, cell: Cell, side: Side,
@@ -1035,6 +1063,29 @@ const CARD_EFFECTS: Record<string, AttackEffect | NeutralEffect | CounterEffect>
         delete state.createdEdges[pkey];
         events.push({ type: "wallDestroyed", caster: caster.id, edge: pair, wasDoor: false });
       }
+      // Breaching the maze's outer rim breaks through BOTH sides — the
+      // default wraparound connects opposite edges, so a new warp opens
+      // (rules rev 19; sector moves recompute openings and forget it).
+      const offBoard = !view.cells[cellKey(neighbor(cell, side))];
+      if ((state.config.deckRev ?? 1) >= 19 && offBoard && !pair) {
+        const far = oppositePerimeter(view, cell, side);
+        const farKey = far ? edgeKey(far.cell, far.side) : "";
+        if (far && (boardView(state).edges[farKey] ?? "open") === "wall") {
+          state.edgeOverrides[farKey] = "open";
+          delete state.createdEdges[farKey];
+          events.push({ type: "wallDestroyed", caster: caster.id, edge: far, wasDoor: false });
+          for (const p of state.players) {
+            if (p.alive && cellKey(p.position) === cellKey(far.cell)) {
+              applyDamage(state, events, p, 4, "collapsing wall", caster.id, "physical");
+            }
+          }
+          state.board.warps.push(
+            { from: { cell, side }, to: { cell: far.cell, side: far.side } },
+            { from: { cell: far.cell, side: far.side }, to: { cell, side } },
+          );
+          events.push({ type: "warpOpened", a: { cell, side }, b: far });
+        }
+      }
       for (const c of [cell, neighbor(cell, side)]) {
         for (const p of state.players) {
           if (p.alive && cellKey(p.position) === cellKey(c)) {

packages/engine/test/board.test.ts

@@ -9,6 +9,7 @@ import {
   type SectorPlacement,
 } from "../src/board";
 import { buildDeck } from "../src/cards";
+import { edgeKey, type Side } from "../src/board";
 import { activePlayer, applyCommand, boardView, createGame, gameLos } from "../src/game";
 import { createRng } from "../src/rng";
 import { setupBoard } from "../src/setups";
@@ -279,3 +280,38 @@ describe("bricking over a warp mouth", () => {
     expect(stepTarget(boardView(r2.state), w.from.cell, w.from.side).kind).toBe("warp");
   });
 });
+
+describe("breaching the rim (rules rev 19)", () => {
+  it("destroying a perimeter wall opens both sides as a new warp", () => {
+    let { state } = createGame({ playerIds: ["a", "b"], seed: 42, sets: ["basic"], deckRev: 19 });
+    for (let i = 0; i < 2; i++) {
+      const r = applyCommand(state, activePlayer(state).id, { type: "endTurn", draw: 0 });
+      if (!r.ok) throw new Error(r.error);
+      state = r.state;
+    }
+    // Find a rim wall with a wrap counterpart that is NOT already an opening.
+    const view = boardView(state);
+    for (const key of Object.keys(view.cells)) {
+      const [x, y] = key.split(",").map(Number) as [number, number];
+      for (const side of ["N", "E", "S", "W"] as Side[]) {
+        const n = { x: x + (side === "E" ? 1 : side === "W" ? -1 : 0), y: y + (side === "S" ? 1 : side === "N" ? -1 : 0) };
+        if (view.cells[`${n.x},${n.y}`]) continue;
+        if ((view.edges[edgeKey({ x, y }, side)] ?? "open") !== "wall") continue;
+        const caster = activePlayer(state);
+        caster.position = { x, y };
+        caster.hand[0] = { instanceId: "dw#1", cardId: "destroy-wall" };
+        const warpsBefore = state.board.warps.length;
+        const r = applyCommand(state, caster.id, {
+          type: "cast", instanceId: "dw#1", target: { kind: "edge", cell: { x, y }, side },
+        });
+        if (!r.ok) throw new Error(r.error);
+        if (r.state.board.warps.length === warpsBefore) continue; // no counterpart in this row
+        expect(r.state.board.warps.length).toBe(warpsBefore + 2);
+        const w = r.state.board.warps[warpsBefore]!;
+        expect(stepTarget(boardView(r.state), w.from.cell, w.from.side).kind).toBe("warp");
+        return;
+      }
+    }
+    throw new Error("setup: no breachable rim wall found");
+  });
+});