fix(search): prevent stale navigation from clobbering focused search input

The sync $effect on the home page unconditionally overwrote the local `q`
state with the URL value after every navigation. When users typed faster
than a navigation round-trip (debounce fires → goto() → data reloads),
the completed navigation wrote the stale URL value back into the input,
dropping the characters typed in the interim.

Guard the `q` assignment in the effect with a `qFocused` flag (set via
onfocus/onblur on the text input). Covers issue #34.

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

frontend/src/routes/+page.svelte

@@ -11,6 +11,7 @@ import { formatDate } from '$lib/utils/date';
 let { data } = $props();
 
 let q = $state(untrack(() => data.filters?.q || ''));
+let qFocused = $state(false);
 let from = $state(untrack(() => data.filters?.from || ''));
 let to = $state(untrack(() => data.filters?.to || ''));
 let senderId = $state(untrack(() => data.filters?.senderId || ''));
@@ -61,9 +62,10 @@ $effect(() => {
 	}
 });
 
-// Sync local state with server data after navigation
+// Sync local state with server data after navigation.
+// Guard q: skip overwrite while the user is actively typing in the search field.
 $effect(() => {
-	q = data.filters?.q || '';
+	if (!qFocused) q = data.filters?.q || '';
 	from = data.filters?.from || '';
 	to = data.filters?.to || '';
 	senderId = data.filters?.senderId || '';
@@ -85,6 +87,8 @@ $effect(() => {
 					type="text"
 					bind:value={q}
 					oninput={handleTextSearch}
+					onfocus={() => (qFocused = true)}
+					onblur={() => (qFocused = false)}
 					placeholder={m.docs_search_placeholder()}
 					class="block w-full border-gray-300 py-2.5 pr-10 pl-3 placeholder-gray-400 shadow-sm focus:border-brand-navy focus:ring-brand-navy"
 				/>

frontend/src/routes/page.svelte.spec.ts

@@ -164,6 +164,27 @@ describe('Home page – document list', () => {
 	});
 });
 
+// ─── Keystroke preservation (issue #34) ──────────────────────────────────────
+
+describe('Home page – search input keystroke preservation', () => {
+	it('does not overwrite the search input while the user is focused and stale data arrives', async () => {
+		const { rerender } = render(Page, { data: emptyData });
+
+		const input = page.getByPlaceholder('Suche in Titel, Inhalt, Ort...');
+
+		// User types "abc" — input is focused
+		await input.click();
+		await input.fill('abc');
+
+		// Simulate a navigation completing with stale data (q='a') while the user is still typing
+		await rerender({ data: { ...emptyData, filters: { ...emptyData.filters, q: 'a' } } });
+		await tick();
+
+		// Input must still show what the user typed, not the stale URL value
+		await expect.element(input).toHaveValue('abc');
+	});
+});
+
 // ─── Error state ──────────────────────────────────────────────────────────────
 
 describe('Home page – error state', () => {