feat(documents): prefill sender and receiver from URL params on new document page

When navigating from the conversations page via the 'New document in this
correspondence' link, the senderId and receiverId query params are now read
in the server load, resolved to person names, and used to pre-populate the
sender typeahead and receiver multi-select on the form.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/routes/documents/new/+page.server.ts

@@ -5,10 +5,12 @@ import { parseBackendError, getErrorMessage } from '$lib/errors';
 
 export async function load({
 	fetch,
-	locals
+	locals,
+	url
 }: {
 	fetch: typeof globalThis.fetch;
 	locals: App.Locals;
+	url: URL;
 }) {
 	const canWrite =
 		locals.user?.groups?.some((g: { permissions: string[] }) =>
@@ -16,14 +18,41 @@ export async function load({
 		) ?? false;
 	if (!canWrite) throw error(403, 'Forbidden');
 
-	const api = createApiClient(fetch);
-	const personsResult = await api.GET('/api/persons');
+	const senderId = url.searchParams.get('senderId') || '';
+	const receiverId = url.searchParams.get('receiverId') || '';
 
-	if (!personsResult.response.ok) {
-		return { persons: [] };
+	const api = createApiClient(fetch);
+
+	let initialSenderName = '';
+	let initialReceivers: { id: string; firstName: string; lastName: string }[] = [];
+
+	const requests: Promise<void>[] = [];
+
+	if (senderId) {
+		requests.push(
+			api.GET('/api/persons/{id}', { params: { path: { id: senderId } } }).then(({ data }) => {
+				if (data) initialSenderName = `${data.firstName} ${data.lastName}`;
+			})
+		);
 	}
 
-	return { persons: personsResult.data };
+	if (receiverId) {
+		requests.push(
+			api.GET('/api/persons/{id}', { params: { path: { id: receiverId } } }).then(({ data }) => {
+				if (data)
+					initialReceivers = [{ id: data.id!, firstName: data.firstName, lastName: data.lastName }];
+			})
+		);
+	}
+
+	const [personsResult] = await Promise.all([api.GET('/api/persons'), ...requests]);
+
+	return {
+		persons: personsResult.response.ok ? personsResult.data : [],
+		initialSenderId: senderId,
+		initialSenderName,
+		initialReceivers
+	};
 }
 
 export const actions = {

frontend/src/routes/documents/new/+page.svelte

@@ -5,11 +5,13 @@ import PersonTypeahead from '$lib/components/PersonTypeahead.svelte';
 import PersonMultiSelect from '$lib/components/PersonMultiSelect.svelte';
 import { m } from '$lib/paraglide/messages.js';
 
-let { form } = $props();
+let { data, form } = $props();
 
 let tags: string[] = $state([]);
-let senderId = $state('');
-let selectedReceivers: { id: string; firstName: string; lastName: string }[] = $state([]);
+let senderId = $state(data.initialSenderId);
+let selectedReceivers: { id: string; firstName: string; lastName: string }[] = $state(
+	data.initialReceivers
+);
 
 let dateDisplay = $state('');
 let dateIso = $state('');
@@ -120,7 +122,12 @@ function handleDateInput(e: Event) {
 
 				<!-- Absender -->
 				<div>
-					<PersonTypeahead name="senderId" label={m.form_label_sender()} bind:value={senderId} />
+					<PersonTypeahead
+						name="senderId"
+						label={m.form_label_sender()}
+						bind:value={senderId}
+						initialName={data.initialSenderName}
+					/>
 				</div>
 
 				<!-- Empfänger -->