Implement the 023-clear-encounter feature that adds a clear encounter button with confirmation dialog to remove all combatants and reset round/turn counters, with the cleared state persisting across page refreshes

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/domain/src/__tests__/clear-encounter.test.ts

@@ -0,0 +1,114 @@
+import { describe, expect, it } from "vitest";
+import { clearEncounter } from "../clear-encounter.js";
+import type { DomainError, Encounter } from "../types.js";
+import { combatantId, createEncounter, isDomainError } from "../types.js";
+
+function makeEncounter(
+	count: number,
+	overrides?: Partial<Encounter>,
+): Encounter {
+	const combatants = Array.from({ length: count }, (_, i) => ({
+		id: combatantId(`c-${i + 1}`),
+		name: `Combatant ${i + 1}`,
+	}));
+
+	const result = createEncounter(combatants);
+	if (isDomainError(result)) {
+		throw new Error("Failed to create encounter in test helper");
+	}
+
+	return { ...result, ...overrides };
+}
+
+describe("clearEncounter", () => {
+	it("clears encounter with multiple combatants at round 3 — returns empty encounter with roundNumber 1 and activeIndex 0", () => {
+		const encounter = makeEncounter(4, { roundNumber: 3, activeIndex: 2 });
+
+		const result = clearEncounter(encounter);
+
+		expect(isDomainError(result)).toBe(false);
+		const success = result as Exclude<typeof result, DomainError>;
+		expect(success.encounter.combatants).toEqual([]);
+		expect(success.encounter.roundNumber).toBe(1);
+		expect(success.encounter.activeIndex).toBe(0);
+	});
+
+	it("clears encounter with a single combatant", () => {
+		const encounter = makeEncounter(1);
+
+		const result = clearEncounter(encounter);
+
+		expect(isDomainError(result)).toBe(false);
+		const success = result as Exclude<typeof result, DomainError>;
+		expect(success.encounter.combatants).toEqual([]);
+		expect(success.encounter.activeIndex).toBe(0);
+		expect(success.encounter.roundNumber).toBe(1);
+	});
+
+	it("clears encounter with combatants that have HP/AC/conditions/concentration", () => {
+		const encounter: Encounter = {
+			combatants: [
+				{
+					id: combatantId("c-1"),
+					name: "Fighter",
+					maxHp: 50,
+					currentHp: 30,
+					ac: 18,
+					conditions: ["blinded", "poisoned"],
+					isConcentrating: true,
+				},
+				{
+					id: combatantId("c-2"),
+					name: "Wizard",
+					maxHp: 25,
+					currentHp: 0,
+					ac: 12,
+					conditions: ["unconscious"],
+				},
+			],
+			activeIndex: 0,
+			roundNumber: 5,
+		};
+
+		const result = clearEncounter(encounter);
+
+		expect(isDomainError(result)).toBe(false);
+		const success = result as Exclude<typeof result, DomainError>;
+		expect(success.encounter.combatants).toEqual([]);
+	});
+
+	it("returns DomainError with code 'encounter-already-empty' when encounter has no combatants", () => {
+		const encounter: Encounter = {
+			combatants: [],
+			activeIndex: 0,
+			roundNumber: 1,
+		};
+
+		const result = clearEncounter(encounter);
+
+		expect(isDomainError(result)).toBe(true);
+		const error = result as DomainError;
+		expect(error.code).toBe("encounter-already-empty");
+	});
+
+	it("emits EncounterCleared event with correct combatantCount", () => {
+		const encounter = makeEncounter(3);
+
+		const result = clearEncounter(encounter);
+
+		expect(isDomainError(result)).toBe(false);
+		const success = result as Exclude<typeof result, DomainError>;
+		expect(success.events).toEqual([
+			{ type: "EncounterCleared", combatantCount: 3 },
+		]);
+	});
+
+	it("is deterministic — same input always produces same output", () => {
+		const encounter = makeEncounter(2, { roundNumber: 4, activeIndex: 1 });
+
+		const result1 = clearEncounter(encounter);
+		const result2 = clearEncounter(encounter);
+
+		expect(result1).toEqual(result2);
+	});
+});