Unify UI workflows and streamline fleet management

src/lib/ui/poll.ts

@@ -0,0 +1,25 @@
+/** Poll visible page content without overlapping requests. Fleet watches use their own monitor. */
+export function pollVisible(task: () => void | Promise<unknown>, interval: number, immediate = true): () => void {
+    let stopped = false;
+    let running = false;
+    let timer: ReturnType<typeof setTimeout> | undefined;
+    const visible = () => document.visibilityState !== 'hidden';
+    const run = async () => {
+        if (stopped || running || !visible()) return;
+        clearTimeout(timer);
+        running = true;
+        try { await task(); }
+        catch (error) { console.error('Page refresh failed', error); }
+        finally {
+            running = false;
+            if (!stopped && visible()) timer = setTimeout(run, interval);
+        }
+    };
+    const visibility = () => {
+        clearTimeout(timer);
+        if (document.visibilityState !== 'hidden') void run();
+    };
+    document.addEventListener('visibilitychange', visibility);
+    if (immediate) void run(); else timer = setTimeout(run, interval);
+    return () => { stopped = true; clearTimeout(timer); document.removeEventListener('visibilitychange', visibility); };
+}