The Alter Ego casts from its own square; the first-stride cue leaves the maze

Randy raised his double, selected it, and could cast nothing through
it: the card's whole point — "it may use any of the spells in your
hand, and you need not be in its L.O.S." — had never been wired. A
cast may now name the double, and the double's square becomes the
spell's origin: sight, reach, the launch point the reel films, and
the direction a knockback or rout pushes. The hand, the attack, and
every answer to it stay the caster's. Spells that move the caster's
own body — a goat's charge, a swap — do not travel through it. On the
board, the double's sight lights the eligible squares; selecting the
double and then a card aims from where it stands. A test hides the
caster and fires through the double.

The first-stride caption sat on the maze and hid the walls beside the
wizard; it now stands above the board with a color chip for "you."

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Jm2auWk6RP71CjaAb4FMoG

packages/engine/test/creatures.test.ts

@@ -1,9 +1,10 @@
 import { describe, expect, it } from "vitest";
 import {
-  type CreatureState, applyCommand, activePlayer, boardView, creatureAt, type GameState, type PlayerId, createGame } from "../src/game";
+  type CreatureState, applyCommand, activePlayer, boardView, creatureAt, type GameState, type PlayerId, createGame, gameLos,
+} from "../src/game";
 import { cellKey, edgeKey, neighbor, opposite, SIDES, stepTarget, type Cell, type Side } from "../src/board";
 import type { CardInstance } from "../src/cards";
-import { newExpansionGame as newGame, must, drain, giveCard, toRound2, emptyNeighborCell, pushSustained } from "./helpers";
+import { newExpansionGame as newGame, must, drain, giveCard, toRound2, emptyNeighborCell, pushSustained, faceOff } from "./helpers";
 
 /** Summon a creature next to its creator (round 2+, consumes the attack). */
 function summon(state: GameState, playerId: PlayerId, kind: string, tag = "S") {
@@ -961,3 +962,38 @@ describe("the imp's fire is a spell (rev 8)", () => {
     expect(after.alive).toBe(true);
   });
 });
+
+describe("the alter ego casts from its own square", () => {
+  it("a fireball leaves from the double, by the double's sight, and answers to the caster", () => {
+    let { state } = newGame(42);
+    state = toRound2(state);
+    const { attacker, defender } = faceOff(state);
+    const a = state.players.find((p) => p.id === attacker)!;
+    const d = state.players.find((p) => p.id === defender)!;
+    const ego = giveCard(state, attacker, "alter-ego");
+    state = must(state, attacker, { type: "cast", instanceId: ego.instanceId });
+    const double = state.creatures.find((c) => c.kind === "alter-ego" && c.controllerId === attacker)!;
+    expect(cellKey(double.position)).toBe(cellKey(a.position));
+    // The caster steps out of the defender's sight; the double keeps it.
+    const view = boardView(state);
+    const hidden = Object.keys(view.cells).map((k) => { const [x, y] = k.split(",").map(Number) as [number, number]; return { x, y }; })
+      .find((c) => !gameLos(state, c, d.position) && !state.squareContents[cellKey(c)] && !view.homes.some((h) => cellKey(h) === cellKey(c)));
+    expect(hidden).toBeDefined();
+    const me = state.players.find((p) => p.id === attacker)!;
+    me.position = { ...hidden! };
+    const fb = giveCard(state, attacker, "fireball");
+    const blind = applyCommand(state, attacker, { type: "cast", instanceId: fb.instanceId, target: { kind: "player", playerId: defender } });
+    expect(blind.ok).toBe(false);
+    const wrong = applyCommand(state, attacker, { type: "cast", instanceId: fb.instanceId, target: { kind: "player", playerId: defender }, via: "no-such-double" });
+    expect(wrong.ok).toBe(false);
+    const viaEgo = applyCommand(state, attacker, { type: "cast", instanceId: fb.instanceId, target: { kind: "player", playerId: defender }, via: double.id });
+    expect(viaEgo.ok).toBe(true);
+    if (!viaEgo.ok) return;
+    expect(viaEgo.state.stack?.attackerId).toBe(attacker);
+    expect(cellKey(viaEgo.state.stack!.origin!)).toBe(cellKey(double.position));
+    const cast = viaEgo.events.find((e) => e.type === "spellCast");
+    expect(cast && cast.type === "spellCast" ? cellKey(cast.from) : null).toBe(cellKey(double.position));
+    const done = must(viaEgo.state, defender, { type: "pass" });
+    expect(done.players.find((p) => p.id === defender)!.life).toBe(10);
+  });
+});