feat: module 02 action queue

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

course/02-action-queue/reference/ts/src/engine/card.ts

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+// Card definitions as the engine sees them. The definitions themselves live in `content`.
+
+import type { Action, Ctx } from "./queue";
+
+/**
+ * A card's behaviour: given where and for whom it runs, the actions to perform.
+ * Module 2 writes these as functions in `content`; Module 5 turns them into data.
+ */
+export type EffectFn = (ctx: Ctx) => Action[];
+
+/** What a triggered ability listens for. */
+export type TriggerOn =
+  | "selfDamaged" // this minion takes damage
+  | "friendlyMinionDamaged" // a minion with the same owner (this one included) takes damage
+  | "anyMinionDamaged" // any minion takes damage
+  | "heroDamaged"; // either hero takes damage
+
+/** The trigger's family name, as reported in `Triggered` events. */
+export function triggerLabel(on: TriggerOn): string {
+  switch (on) {
+    case "selfDamaged":
+    case "friendlyMinionDamaged":
+    case "anyMinionDamaged":
+    case "heroDamaged":
+      return "damaged";
+  }
+}
+
+export interface Trigger {
+  on: TriggerOn;
+  effect: EffectFn;
+}
+
+/** What the engine needs to know about a card. */
+export interface CardDef {
+  name: string;
+  attack: number;
+  health: number;
+  /** Triggered abilities, in printed order. */
+  triggers: Trigger[];
+  /** A spell's effect when cast; absent for minions. */
+  onCast?: EffectFn;
+}
+
+export function minion(name: string, attack: number, health: number, triggers: Trigger[] = []): CardDef {
+  return { name, attack, health, triggers };
+}
+
+export function spell(name: string, onCast: EffectFn): CardDef {
+  return { name, attack: 0, health: 0, triggers: [], onCast };
+}
+
+/** Every card the game can create, looked up by name. */
+export class CardLibrary {
+  private readonly cards = new Map<string, CardDef>();
+
+  constructor(defs: CardDef[]) {
+    for (const def of defs) this.cards.set(def.name, def);
+  }
+
+  get(name: string): CardDef {
+    const def = this.cards.get(name);
+    if (!def) throw new Error(`unknown card "${name}": define it in src/content`);
+    return def;
+  }
+}