feat(error-handling): wire window.onerror and unhandledrejection into telemetry sink

src/lib/globalHandlers.ts

@@ -0,0 +1,55 @@
+import { reportError } from './telemetry';
+
+let installed = false;
+let lastSignature = '';
+let lastTimestamp = 0;
+const DEDUP_WINDOW_MS = 5000;
+
+function isDuplicate(sig: string): boolean {
+  const now = Date.now();
+  if (sig === lastSignature && now - lastTimestamp < DEDUP_WINDOW_MS) {
+    return true;
+  }
+  lastSignature = sig;
+  lastTimestamp = now;
+  return false;
+}
+
+export function installGlobalErrorHandlers(): void {
+  if (installed || typeof window === 'undefined') {
+    return;
+  }
+  installed = true;
+
+  window.addEventListener('error', (event: ErrorEvent) => {
+    const errorObj = event.error || new Error(event.message || 'Script error');
+    const sig = ${event.message}::;
+    if (isDuplicate(sig)) return;
+
+    const isResourceLoad = !event.error && event.target instanceof HTMLElement;
+    reportError(errorObj, {
+      source: 'global',
+      operation: 'window.onerror',
+      metadata: {
+        filename: event.filename ? event.filename.split('?')[0] : undefined,
+        lineno: event.lineno,
+        resourceLoad: isResourceLoad
+      }
+    });
+  });
+
+  window.addEventListener('unhandledrejection', (event: PromiseRejectionEvent) => {
+    if (event.reason && (event.reason.name === 'AbortError' || event.reason.code === 20)) {
+      return; // Ignore intentional fetch abortions
+    }
+
+    const err = event.reason instanceof Error ? event.reason : new Error(String(event.reason));
+    const sig = ejection:;
+    if (isDuplicate(sig)) return;
+
+    reportError(err, {
+      source: 'global',
+      operation: 'unhandledrejection'
+    });
+  });
+}