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/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,