Fix false stale Fleet reports caused by clock skew

src/lib/ui/stores/servers.ts

@@ -46,15 +46,36 @@ export const statusReceivedAt = writable(0);
 // startServerStream() call in the browser.
 const _uiNow = writable(Date.now());
 export const uiNow = readonly(_uiNow);
+let serverClock: { time: number; receivedAt: number } | null = null;
+
+// Report timestamps belong to the backend clock, which can differ from the
+// browser's wall clock. Advance that clock locally even if updates stop.
+export function serverTimeNow(): number {
+    return serverClock ? serverClock.time + performance.now() - serverClock.receivedAt : Date.now();
+}
+
+export function syncServerTime(serverNow?: number): void {
+    if (typeof serverNow === 'number' && Number.isFinite(serverNow)) {
+        // A delayed HTTP snapshot must not rewind time behind a newer stream
+        // update and make that update look like it came from the future.
+        const time = serverClock ? Math.max(serverNow, serverTimeNow()) : serverNow;
+        serverClock = { time, receivedAt: performance.now() };
+    }
+    // Refresh immediately: a suspended tab's interval may be well behind.
+    _uiNow.set(serverTimeNow());
+}
+
 let tickInterval: ReturnType<typeof setInterval> | null = null;
 
 let source: EventSource | null = null;
 
 export function startServerStream(): (() => void) | undefined {
     if (!browser || source) return;
+    syncServerTime();
     source = new EventSource('/api/events/servers');
     source.addEventListener('server-telemetry', (evt) => {
-        const data = JSON.parse((evt as MessageEvent).data) as { entries: GameTelemetry[]; snapshot?: boolean };
+        const data = JSON.parse((evt as MessageEvent).data) as { entries: GameTelemetry[]; snapshot?: boolean; serverNow?: number };
+        syncServerTime(data.serverNow);
         telemetryByServer.update((previous) => {
             const next = data.snapshot ? new Map<string, GameTelemetry>() : new Map(previous);
             for (const entry of data.entries) next.set(entry.server, entry);
@@ -62,7 +83,8 @@ export function startServerStream(): (() => void) | undefined {
         });
     });
     source.addEventListener('server-status', (evt) => {
-        const data = JSON.parse((evt as MessageEvent).data) as { entries: ServerStatus[] };
+        const data = JSON.parse((evt as MessageEvent).data) as { entries: ServerStatus[]; serverNow?: number };
+        syncServerTime(data.serverNow);
         statusByServer.update(() => {
             const m = new Map<string, ServerStatus>();
             for (const e of data.entries) m.set(e.server, e);
@@ -71,7 +93,7 @@ export function startServerStream(): (() => void) | undefined {
         statusReceivedAt.set(Date.now());
     });
     if (tickInterval === null) {
-        tickInterval = setInterval(() => _uiNow.set(Date.now()), 1000);
+        tickInterval = setInterval(() => _uiNow.set(serverTimeNow()), 1000);
     }
     return () => { source?.close(); source = null; if (tickInterval) clearInterval(tickInterval); tickInterval = null; };
 }