fix(apps): stop task.yaml rewrite races + blank-load watchdog + loop-lag monitor

Investigating 'apps blank while a bg task runs': measured serving latency
through a real scheduled bg-task run — 1-3ms on both loopbacks throughout,
so the server is not the bottleneck. Found and fixed the likely renderer-era
culprit plus made the failure observable:

- agent sync (apps:list, polled every 4s) rewrote each bundled agent's
  task.yaml unconditionally — racing the bg runner's own patches mid-run and
  spamming watcher events; now writes only when the definition changed
- AppFrame load watchdog: if the iframe hasn't loaded in 6s, show a visible
  'taking too long' state with Retry instead of a silent blank pane
- main event-loop lag monitor: stalls >300ms are logged so future blank
  reports can be tied to the offending work

apps/x/packages/core/src/apps/agents.ts

@@ -59,6 +59,9 @@ async function materializeAgent(folder: string, agentFile: string): Promise<stri
 
     if (await pathExists(taskYaml)) {
         // Update path (§8.4): overwrite definition fields, preserve the rest.
+        // Write ONLY when the definition actually changed — this sync runs on
+        // every apps:list poll, and an unconditional rewrite races the bg
+        // runner's own task.yaml patches mid-run (and spams watcher events).
         try {
             const current = parseYaml(await fs.readFile(taskYaml, 'utf-8')) as BackgroundTask;
             const next: BackgroundTask = {
@@ -69,7 +72,14 @@ async function materializeAgent(folder: string, agentFile: string): Promise<stri
                 sourceApp: folder,
             };
             if (!def.triggers) delete next.triggers;
-            await fs.writeFile(taskYaml, stringifyYaml(next), 'utf-8');
+            const unchanged =
+                current.name === next.name &&
+                current.instructions === next.instructions &&
+                current.sourceApp === next.sourceApp &&
+                JSON.stringify(current.triggers ?? null) === JSON.stringify(next.triggers ?? null);
+            if (!unchanged) {
+                await fs.writeFile(taskYaml, stringifyYaml(next), 'utf-8');
+            }
         } catch (e) {
             console.warn(`[Apps] failed to update agent task ${slug}:`, e);
         }

apps/x/packages/core/src/apps/server.ts

@@ -710,6 +710,27 @@ export function getServerStatus(): { running: boolean; error?: string } {
     return server ? { running: true } : { running: false, ...(serverError ? { error: serverError } : {}) };
 }
 
+let lagMonitor: NodeJS.Timeout | null = null;
+
+/**
+ * Event-loop lag monitor: the apps server shares the main process with agent
+ * runs, sync pipelines, etc. If the loop stalls, every open app hangs with it —
+ * log stalls >300ms so "app went blank" reports can be tied to a culprit.
+ */
+function startLagMonitor(): void {
+    if (lagMonitor) return;
+    let last = Date.now();
+    lagMonitor = setInterval(() => {
+        const now = Date.now();
+        const lag = now - last - 500;
+        if (lag > 300) {
+            console.warn(`[Apps] main event-loop stalled ~${lag}ms (apps server shares this loop — open apps hang during stalls)`);
+        }
+        last = now;
+    }, 500);
+    lagMonitor.unref?.();
+}
+
 export async function init(): Promise<void> {
     if (server) return;
     if (startPromise) return startPromise;
@@ -717,6 +738,7 @@ export async function init(): Promise<void> {
     startPromise = (async () => {
         try {
             await fsp.mkdir(APPS_DIR, { recursive: true });
+            startLagMonitor();
             await startWatcher();
             const expressApp = createApp();
             await new Promise<void>((resolve, reject) => {