fix(typeahead): surface search failures instead of an empty dropdown

The document picker parsed the response without checking r.ok, so a 401/500
rendered identically to 'no matches' and the dropdown silently vanished —
which is how the broken relevance path shipped invisibly. The fetch now
throws on non-OK, the useTypeahead hook exposes an error flag, and the
picker renders a visible failure message (de/en/es).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/messages/de.json

@@ -301,6 +301,7 @@
 	"comp_multiselect_placeholder": "Namen tippen...",
 	"comp_multiselect_remove": "Entfernen",
 	"comp_multiselect_loading": "Suche...",
+	"comp_typeahead_error": "Suche fehlgeschlagen. Bitte versuchen Sie es erneut.",
 	"comp_taginput_placeholder_create": "Schlagworte hinzufügen...",
 	"comp_taginput_placeholder_filter": "Nach Schlagworten filtern...",
 	"comp_taginput_remove": "Schlagwort entfernen",

frontend/messages/en.json

@@ -301,6 +301,7 @@
 	"comp_multiselect_placeholder": "Type a name...",
 	"comp_multiselect_remove": "Remove",
 	"comp_multiselect_loading": "Searching...",
+	"comp_typeahead_error": "Search failed. Please try again.",
 	"comp_taginput_placeholder_create": "Add tags...",
 	"comp_taginput_placeholder_filter": "Filter by tags...",
 	"comp_taginput_remove": "Remove tag",

frontend/messages/es.json

@@ -301,6 +301,7 @@
 	"comp_multiselect_placeholder": "Escriba un nombre...",
 	"comp_multiselect_remove": "Eliminar",
 	"comp_multiselect_loading": "Buscando...",
+	"comp_typeahead_error": "La búsqueda falló. Inténtelo de nuevo.",
 	"comp_taginput_placeholder_create": "Añadir etiquetas...",
 	"comp_taginput_placeholder_filter": "Filtrar por etiquetas...",
 	"comp_taginput_remove": "Eliminar etiqueta",

frontend/src/lib/document/DocumentPickerDropdown.svelte

@@ -62,13 +62,15 @@ function handleSelect(doc: DocumentOption) {
 		class="block w-full rounded border border-line bg-surface px-3 py-2 text-sm text-ink placeholder:text-ink-3 focus:outline-none focus-visible:ring-2 focus-visible:ring-focus-ring"
 	/>
 
-	{#if picker.isOpen && (picker.results.length > 0 || picker.loading)}
+	{#if picker.isOpen && (picker.results.length > 0 || picker.loading || picker.error)}
 		<ul
 			id={listboxId}
 			class="ring-opacity-5 absolute z-50 mt-1 max-h-60 w-full overflow-auto rounded-md bg-surface py-1 text-sm shadow-lg ring-1 ring-black"
 		>
 			{#if picker.loading}
 				<li class="px-3 py-2 text-ink-2">{m.comp_multiselect_loading()}</li>
+			{:else if picker.error}
+				<li role="alert" class="px-3 py-2 text-danger">{m.comp_typeahead_error()}</li>
 			{:else}
 				{#each picker.results as doc (doc.id)}
 					{@const disabled = alreadyAddedIds.has(doc.id!)}

frontend/src/lib/document/DocumentPickerDropdown.svelte.spec.ts

@@ -2,6 +2,7 @@ import { afterEach, describe, expect, it, vi } from 'vitest';
 import { cleanup, render } from 'vitest-browser-svelte';
 import { page, userEvent } from 'vitest/browser';
 import DocumentPickerDropdown from './DocumentPickerDropdown.svelte';
+import { m } from '$lib/paraglide/messages.js';
 
 const waitForDebounce = () => new Promise((r) => setTimeout(r, 350));
 
@@ -93,3 +94,24 @@ describe('DocumentPickerDropdown — selection', () => {
 		expect(onSelect).not.toHaveBeenCalled();
 	});
 });
+
+describe('DocumentPickerDropdown — search failure', () => {
+	it('shows an error message when the search request fails instead of vanishing', async () => {
+		// 500 from /api/documents/search — must surface, not render as "no results"
+		vi.stubGlobal(
+			'fetch',
+			vi.fn().mockResolvedValue({
+				ok: false,
+				status: 500,
+				json: vi.fn().mockResolvedValue({ code: 'INTERNAL_ERROR' })
+			})
+		);
+
+		render(DocumentPickerDropdown, { onSelect: vi.fn() });
+
+		await userEvent.fill(page.getByRole('combobox'), 'Brief');
+		await waitForDebounce();
+
+		await expect.element(page.getByText(m.comp_typeahead_error())).toBeInTheDocument();
+	});
+});

frontend/src/lib/document/documentTypeahead.ts

@@ -14,7 +14,12 @@ export function createDocumentTypeahead() {
 	return createTypeahead<DocumentOption>({
 		fetchUrl: (q) =>
 			fetch(`/api/documents/search?q=${encodeURIComponent(q)}&size=10`)
-				.then((r) => r.json())
+				.then((r) => {
+					// Without this check a 401/500 parses as JSON without `items` and
+					// renders as "no results" — errors must reach the hook's error state.
+					if (!r.ok) throw new Error(`document search failed: ${r.status}`);
+					return r.json();
+				})
 				.then((b: { items: DocumentListItem[] }) =>
 					b.items.map((it) => ({
 						id: it.id,

frontend/src/lib/shared/hooks/useTypeahead.svelte.test.ts

@@ -78,6 +78,34 @@ describe('createTypeahead', () => {
 		errorSpy.mockRestore();
 	});
 
+	it('fetch error sets the error flag so callers can render a failure state', async () => {
+		const fetchUrl = vi.fn().mockRejectedValue(new Error('500'));
+		const errorSpy = vi.spyOn(console, 'error').mockImplementation(() => {});
+		const ta = createTypeahead({ fetchUrl, debounceMs: 0 });
+		expect(ta.error).toBe(false);
+		ta.setQuery('foo');
+		await vi.advanceTimersByTimeAsync(0);
+		expect(ta.error).toBe(true);
+		errorSpy.mockRestore();
+	});
+
+	it('error flag clears on the next successful fetch', async () => {
+		const fetchUrl = vi
+			.fn()
+			.mockRejectedValueOnce(new Error('500'))
+			.mockResolvedValueOnce([{ id: '1' }]);
+		const errorSpy = vi.spyOn(console, 'error').mockImplementation(() => {});
+		const ta = createTypeahead({ fetchUrl, debounceMs: 0 });
+		ta.setQuery('foo');
+		await vi.advanceTimersByTimeAsync(0);
+		expect(ta.error).toBe(true);
+		ta.setQuery('foob');
+		await vi.advanceTimersByTimeAsync(0);
+		expect(ta.error).toBe(false);
+		expect(ta.results).toEqual([{ id: '1' }]);
+		errorSpy.mockRestore();
+	});
+
 	it('setActiveIndex updates activeIndex', () => {
 		const ta = createTypeahead({ fetchUrl: vi.fn().mockResolvedValue([]) });
 		expect(ta.activeIndex).toBe(-1);

frontend/src/lib/shared/hooks/useTypeahead.svelte.ts

@@ -11,6 +11,7 @@ export function createTypeahead<T>(options: Options<T>) {
 	let results: T[] = $state([]);
 	let isOpen = $state(false);
 	let loading = $state(false);
+	let error = $state(false);
 	let activeIndex = $state(-1);
 
 	let debounceTimer: ReturnType<typeof setTimeout> | undefined;
@@ -21,11 +22,13 @@ export function createTypeahead<T>(options: Options<T>) {
 		clearTimeout(debounceTimer);
 		debounceTimer = setTimeout(async () => {
 			loading = true;
+			error = false;
 			try {
 				results = await fetchUrl(q);
 			} catch (e) {
 				console.error('typeahead fetch error', e);
 				results = [];
+				error = true;
 			} finally {
 				loading = false;
 			}
@@ -65,6 +68,9 @@ export function createTypeahead<T>(options: Options<T>) {
 		get loading() {
 			return loading;
 		},
+		get error() {
+			return error;
+		},
 		get activeIndex() {
 			return activeIndex;
 		},