Update effect resolver for indexed player/enemy targets

Added tests and verified resolveEffects handles {type, index}
descriptors for multi-player and multi-enemy state. getEntity and
setEntity helpers resolve either legacy string keys or typed index
objects, so all existing string-based call sites continue working.

src/effects.js

@@ -36,11 +36,7 @@ function getEntity(state, descriptor) {
 
 function setEntity(state, descriptor, updated) {
   if (typeof descriptor === "string") {
-    const next = { ...state, [descriptor]: updated };
-    // keep compat alias in sync
-    if (descriptor === "player") next.player = updated;
-    if (descriptor === "enemy") next.enemy = updated;
-    return next;
+    return { ...state, [descriptor]: updated };
   }
   if (descriptor.type === "player") {
     const players = state.players.map((p, i) =>
@@ -77,9 +73,15 @@ function resolveSingleEffect(state, effect, source, target) {
       return applyStatus(state, target, "weak", effect.value, 3);
     case "strength":
       return applyStatus(state, source, "strength", effect.value, 8);
-    case "draw":
-      return drawCards(state, effect.value);
+    case "draw": {
+      const playerIdx =
+        typeof source === "object" && source.type === "player"
+          ? source.index
+          : 0;
+      return drawCards(state, playerIdx, effect.value);
+    }
     case "lose_hp":
+      // lose_hp damages the caster (source), not the target — e.g. Offering, Bloodletting
       return directDamage(state, source, effect.value);
     case "exhaust":
       // handled by playCard — card goes to exhaustPile instead of discardPile

src/effects.test.js

@@ -148,3 +148,111 @@ describe("resolveEffects - draw", () => {
     expect(next.player.drawPile).toHaveLength(8);
   });
 });
+
+describe("resolveEffects - lose_hp", () => {
+  test("lose_hp damages the caster (source), not the target", () => {
+    const state = makeState();
+    const enemyHpBefore = state.enemy.hp;
+    const playerHpBefore = state.player.hp;
+    const effects = [{ type: "lose_hp", value: 3 }];
+    const next = resolveEffects(state, effects, "player", "enemy");
+    expect(next.player.hp).toBe(playerHpBefore - 3);
+    expect(next.enemy.hp).toBe(enemyHpBefore);
+  });
+});
+
+describe("resolveEffects - indexed descriptors", () => {
+  function makeMultiState(overrides = {}) {
+    const base = createCombatState(
+      ["ironclad", "ironclad"],
+      ["jaw_worm", "jaw_worm"],
+    );
+    return {
+      ...base,
+      players: base.players.map((p, i) =>
+        overrides.players?.[i] ? { ...p, ...overrides.players[i] } : p,
+      ),
+      enemies: base.enemies.map((e, i) =>
+        overrides.enemies?.[i] ? { ...e, ...overrides.enemies[i] } : e,
+      ),
+    };
+  }
+
+  test("hit from player 0 reduces enemy 0 hp, enemy 1 unchanged", () => {
+    const state = makeMultiState();
+    const effects = [{ type: "hit", value: 3 }];
+    const next = resolveEffects(
+      state,
+      effects,
+      { type: "player", index: 0 },
+      { type: "enemy", index: 0 },
+    );
+    expect(next.enemies[0].hp).toBeLessThan(state.enemies[0].hp);
+    expect(next.enemies[1].hp).toBe(state.enemies[1].hp);
+  });
+
+  test("hit from player 1 reduces enemy 1 hp, enemy 0 unchanged", () => {
+    const state = makeMultiState();
+    const effects = [{ type: "hit", value: 2 }];
+    const next = resolveEffects(
+      state,
+      effects,
+      { type: "player", index: 1 },
+      { type: "enemy", index: 1 },
+    );
+    expect(next.enemies[1].hp).toBeLessThan(state.enemies[1].hp);
+    expect(next.enemies[0].hp).toBe(state.enemies[0].hp);
+  });
+
+  test("block applies to player 1 only", () => {
+    const state = makeMultiState();
+    const effects = [{ type: "block", value: 4 }];
+    const next = resolveEffects(
+      state,
+      effects,
+      { type: "player", index: 1 },
+      { type: "enemy", index: 0 },
+    );
+    expect(next.players[1].block).toBe(4);
+    expect(next.players[0].block).toBe(0);
+  });
+
+  test("vulnerable applies to enemy 1 only", () => {
+    const state = makeMultiState();
+    const effects = [{ type: "vulnerable", value: 2 }];
+    const next = resolveEffects(
+      state,
+      effects,
+      { type: "player", index: 0 },
+      { type: "enemy", index: 1 },
+    );
+    expect(next.enemies[1].vulnerable).toBe(2);
+    expect(next.enemies[0].vulnerable).toBe(0);
+  });
+
+  test("enemy hits player 0, player 1 hp unchanged", () => {
+    const state = makeMultiState();
+    const effects = [{ type: "hit", value: 2 }];
+    const next = resolveEffects(
+      state,
+      effects,
+      { type: "enemy", index: 0 },
+      { type: "player", index: 0 },
+    );
+    expect(next.players[0].hp).toBeLessThan(state.players[0].hp);
+    expect(next.players[1].hp).toBe(state.players[1].hp);
+  });
+
+  test("draw effect draws for player 1, player 0 hand unchanged", () => {
+    const state = makeMultiState();
+    const effects = [{ type: "draw", value: 3 }];
+    const next = resolveEffects(
+      state,
+      effects,
+      { type: "player", index: 1 },
+      { type: "enemy", index: 0 },
+    );
+    expect(next.players[1].hand).toHaveLength(3);
+    expect(next.players[0].hand).toHaveLength(0);
+  });
+});