feat(framework): core 座位↔视图转换

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

cocoscreator_projects/YouleNexus/assets/framework/core/seat.ts

@@ -0,0 +1,9 @@
+/** 绝对座位 → 以 mySeat 为视角的视图位（自己=0，其余环形顺延）。 */
+export function toView(mySeat: number, targetSeat: number, seatCount: number): number {
+  return ((targetSeat - mySeat) % seatCount + seatCount) % seatCount;
+}
+
+/** 视图位 → 绝对座位（toView 的逆运算）。 */
+export function fromView(mySeat: number, viewSeat: number, seatCount: number): number {
+  return ((viewSeat + mySeat) % seatCount + seatCount) % seatCount;
+}

cocoscreator_projects/framework-tests/core/seat.test.ts

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+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { toView, fromView } from '../../YouleNexus/assets/framework/core/seat.ts';
+
+test('toView：自己永远是视图 0 号位', () => {
+  assert.equal(toView(2, 2, 4), 0); // mySeat=2, target=2 → 0
+});
+
+test('toView：他人按环形相对自己排布', () => {
+  // 4 人桌，我在 2 号位：座位 3→视图1，座位 0→视图2，座位 1→视图3
+  assert.equal(toView(2, 3, 4), 1);
+  assert.equal(toView(2, 0, 4), 2);
+  assert.equal(toView(2, 1, 4), 3);
+});
+
+test('fromView 是 toView 的逆运算', () => {
+  const seatCount = 4, mySeat = 2;
+  for (let s = 0; s < seatCount; s++) {
+    assert.equal(fromView(mySeat, toView(mySeat, s, seatCount), seatCount), s);
+  }
+});