feat(Pairing): add createPairing id factory

src/entities/Pairing/domain/createPairing/createPairing.test.ts

@@ -0,0 +1,22 @@
+import {
+    describe,
+    expect,
+    it,
+} from 'vitest';
+import { createPairing } from './createPairing';
+
+describe('createPairing', () => {
+    it('builds a pairing from two font ids', () => {
+        const p = createPairing('Inter', 'Lora');
+        expect(p.headerFontId).toBe('Inter');
+        expect(p.bodyFontId).toBe('Lora');
+    });
+    it('generates a unique id each call (duplicates stay distinct)', () => {
+        const a = createPairing('Inter', 'Lora');
+        const b = createPairing('Inter', 'Lora');
+        expect(a.id).not.toBe(b.id);
+    });
+    it('accepts an explicit id for rehydration', () => {
+        expect(createPairing('Inter', 'Lora', 'fixed-id').id).toBe('fixed-id');
+    });
+});

src/entities/Pairing/domain/createPairing/createPairing.ts

@@ -0,0 +1,15 @@
+import type { Pairing } from '../types';
+
+/**
+ * Creates a Pairing with a fresh surrogate id (or a supplied one when
+ * rehydrating from storage). The id is identity, never content — two pairings
+ * with the same fonts are still distinct cards.
+ *
+ * @param headerFontId - Font entity id for the header role.
+ * @param bodyFontId - Font entity id for the body role.
+ * @param id - Explicit id for rehydration; defaults to a fresh UUID.
+ * @returns The new Pairing.
+ */
+export function createPairing(headerFontId: string, bodyFontId: string, id: string = crypto.randomUUID()): Pairing {
+    return { id, headerFontId, bodyFontId };
+}