fix: various bugs in observability / OTel (#1564)

frontend/src/routes/+layout.svelte

@@ -4,11 +4,16 @@
 	import Header from '$lib/components/header/header.svelte';
 	import { Toaster } from '$lib/components/ui/sonner';
 	import { m } from '$lib/paraglide/messages';
+	import { startPageTrace } from '$lib/utils/tracing-util';
+	import { beforeNavigate } from '$app/navigation';
 	import { ModeWatcher } from 'mode-watcher';
 	import { type Snippet } from 'svelte';
 	import '../app.css';
 	import type { LayoutData } from './$types';
 
+	// Start a new page-level trace on each navigation so a page view and the API calls it triggers are correlated as a single trace.
+	beforeNavigate((nav) => startPageTrace(nav.to?.url.pathname));
+
 	let {
 		data,
 		children

frontend/src/routes/+layout.ts

@@ -4,6 +4,7 @@ import appConfigStore from '$lib/stores/application-configuration-store';
 import userStore from '$lib/stores/user-store';
 import { setLocaleForLibraries } from '$lib/utils/locale.util';
 import { getAuthRedirectPath } from '$lib/utils/redirection-util';
+import { setTracingEnabled } from '$lib/utils/tracing-util';
 import { redirect } from '@sveltejs/kit';
 import type { LayoutLoad } from './$types';
 
@@ -37,6 +38,10 @@ export const load: LayoutLoad = async ({ url }) => {
 		appConfigStore.set(appConfig);
 	}
 
+	// Only export traces when the backend is configured to forward them; otherwise the SPA would POST spans to an unregistered endpoint.
+	// When enabled this dynamically imports the OpenTelemetry libraries, so awaiting it ensures the tracer provider is ready before any traced navigation or request.
+	await setTracingEnabled(appConfig?.tracingEnabled ?? false);
+
 	await setLocaleForLibraries();
 
 	return {