fix(ui): hide clock warning until first sync settles

读取到校准缓存时 status 会先变成 cached，start() 随即渲染出警告条，
几百毫秒后校准成功又隐藏，表现为每次刷新闪现一次。

新增 hasSettledSync 标记，首次校准有结果前不渲染任何警告。原先只有
local 分支有 syncPromise 守卫，cached 和 stale 分支漏了同样的处理。

src/ui/scripts/time.js

@@ -37,6 +37,7 @@ export function getTimeCode() {
         this.syncAttemptId = 0;
         this.activeSampleControllers = new Set();
         this.started = false;
+        this.hasSettledSync = false;
         this.loadCachedOffset();
       }
 
@@ -248,6 +249,7 @@ export function getTimeCode() {
         this.localWallAtSyncMs = Date.now();
         this.monotonicEpochAtSyncMs = this.monotonicEpochNow();
         this.status = 'synced';
+        this.hasSettledSync = true;
         this.generation += 1;
         this.persistOffset();
         this.renderStatus();
@@ -256,6 +258,7 @@ export function getTimeCode() {
       }
 
       markSyncFailure() {
+        this.hasSettledSync = true;
         this.status = Number.isFinite(this.offsetMs) ? 'cached' : 'local';
         this.renderStatus();
       }
@@ -352,7 +355,11 @@ export function getTimeCode() {
         const isStale = Number.isFinite(ageMs) && ageMs > CLOCK_SYNC_STALE_MS;
         let message = '';
 
-        if (this.status === 'local' && !this.syncPromise) {
+        // 首次校准落地前不提示：页面刚加载时缓存偏移已生效但校准仍在进行，
+        // 此时提示会在校准成功后立即消失，表现为刷新时的一次闪烁。
+        if (!this.hasSettledSync) {
+          message = '';
+        } else if (this.status === 'local') {
           message = '无法校准服务器时间，OTP 正在使用设备时间，可能不正确。';
         } else if (this.status === 'cached') {
           const ageText = this.formatAge(ageMs);

tests/scripts/otp-time-sync.test.js

@@ -548,6 +548,61 @@ describe('trusted browser clock', () => {
 		await expect(backgroundSync).resolves.toBe(true);
 	});
 
+	it('keeps the warning hidden on load while the first sync is still in flight', async () => {
+		const elements = createWarningElements();
+		const harness = createHarness({
+			elements,
+			storageValues: {
+				[STORAGE_KEY]: createCachedClock({
+					offsetMs: 12_000,
+					localWallAtSyncMs: SERVER_BASE_MS - 60 * 60 * 1000,
+				}),
+			},
+		});
+		expect(harness.api.trustedClock.status).toBe('cached');
+
+		harness.queueSamples([20, 40, 60].map((rttMs) => ({ rttMs, offsetMs: 15_000 })));
+		harness.api.trustedClock.start();
+		const initialSync = harness.api.trustedClock.syncPromise;
+
+		expect(elements.clockWarning.hidden).toBe(true);
+		expect(elements.clockWarningText.textContent).toBe('');
+		expect(elements.clockWarning.classList.toggle).not.toHaveBeenCalledWith('show', true);
+
+		await harness.completePendingRequests();
+		await expect(initialSync).resolves.toBe(true);
+
+		expect(harness.api.trustedClock.status).toBe('synced');
+		expect(elements.clockWarning.hidden).toBe(true);
+		expect(elements.clockWarning.classList.toggle).not.toHaveBeenCalledWith('show', true);
+	});
+
+	it('shows the cached warning once the first sync fails instead of before it settles', async () => {
+		const elements = createWarningElements();
+		const harness = createHarness({
+			elements,
+			storageValues: {
+				[STORAGE_KEY]: createCachedClock({
+					offsetMs: 12_000,
+					localWallAtSyncMs: SERVER_BASE_MS - 60 * 60 * 1000,
+				}),
+			},
+		});
+
+		harness.queueSamples([20, 40, 60].map((rttMs) => ({ reject: true, rttMs })));
+		harness.api.trustedClock.start();
+		const initialSync = harness.api.trustedClock.syncPromise;
+		expect(elements.clockWarning.hidden).toBe(true);
+
+		await harness.completePendingRequests();
+		await expect(initialSync).resolves.toBe(false);
+
+		expect(harness.api.trustedClock.status).toBe('cached');
+		expect(elements.clockWarning.hidden).toBe(false);
+		expect(elements.clockWarning.classList.toggle).toHaveBeenLastCalledWith('show', true);
+		expect(elements.clockWarningText.textContent).not.toBe('');
+	});
+
 	it('shows a stale warning after 24 hours during periodic and offline status refreshes', async () => {
 		const elements = createWarningElements();
 		const harness = createHarness({ elements });