fix(geschichte): uniform onSubmit rejects-on-failure contract

The c3afd57e fix made the edit page's handleSubmit throw on !res.ok but
only JourneyEditor caught it. Now: GeschichteEditor.save() catches and
keeps its dirty state (no unhandled rejection -> no GlitchTip noise on a
failed STORY save); StoryCreate throws on failure so a failed STORY
create no longer silently disarms the unsaved guard; both handleSubmit
implementations catch network rejections, surface a message, and rethrow.
Contract documented on both editors' Props. GeschichteEditor also gets
the title maxlength=255. Spec: rejecting onSubmit is caught and the
editor stays usable.

Review round 3: Felix §2, Tobias S1, Nora (3), Markus (concern 1).

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

frontend/src/lib/geschichte/GeschichteEditor.svelte

@@ -14,6 +14,7 @@ type Person = components['schemas']['Person'];
 interface Props {
 	geschichte?: GeschichteView | null;
 	initialPersons?: Person[];
+	/** Must reject when the save failed — the editor keeps its dirty state then. */
 	onSubmit: (payload: {
 		title: string;
 		body: string;
@@ -106,13 +107,17 @@ function handleTitleInput() {
 async function save(nextStatus: 'DRAFT' | 'PUBLISHED') {
 	titleTouched = true;
 	if (titleEmpty) return;
-	await onSubmit({
-		title: title.trim(),
-		body,
-		status: nextStatus,
-		personIds: selectedPersons.map((p) => p.id!).filter(Boolean)
-	});
-	dirty = false;
+	try {
+		await onSubmit({
+			title: title.trim(),
+			body,
+			status: nextStatus,
+			personIds: selectedPersons.map((p) => p.id!).filter(Boolean)
+		});
+		dirty = false;
+	} catch {
+		// onSubmit signalled failure — keep dirty so the unsaved guard stays armed
+	}
 }
 
 function isActive(name: string, attrs?: Record<string, unknown>): boolean {
@@ -135,6 +140,7 @@ function exec(action: () => void) {
 			<input
 				type="text"
 				bind:value={title}
+				maxlength="255"
 				oninput={handleTitleInput}
 				onblur={handleTitleBlur}
 				placeholder={m.geschichte_editor_title_placeholder()}

frontend/src/lib/geschichte/GeschichteEditor.svelte.spec.ts

@@ -54,6 +54,22 @@ describe('GeschichteEditor — title-required guard', () => {
 	});
 });
 
+describe('GeschichteEditor — onSubmit rejects on failure', () => {
+	it('catches a rejecting onSubmit (no unhandled rejection) and stays editable', async () => {
+		// Contract: onSubmit rejects on failure. Without the catch in save(), this
+		// click would surface as an unhandled promise rejection and fail the run.
+		const onSubmit = vi.fn().mockRejectedValue(new Error('save failed'));
+		render(GeschichteEditor, { geschichte: draftFactory(), onSubmit });
+
+		await userEvent.click(page.getByRole('button', { name: 'Entwurf speichern' }));
+		await vi.waitFor(() => expect(onSubmit).toHaveBeenCalledTimes(1));
+
+		// Editor still functional — a second save attempt goes through
+		await userEvent.click(page.getByRole('button', { name: 'Entwurf speichern' }));
+		await vi.waitFor(() => expect(onSubmit).toHaveBeenCalledTimes(2));
+	});
+});
+
 describe('GeschichteEditor — save bar adapts to status', () => {
 	it('renders DRAFT mode buttons when no geschichte prop is supplied', async () => {
 		render(GeschichteEditor, { onSubmit: vi.fn() });

frontend/src/routes/geschichten/[id]/edit/+page.svelte

@@ -35,6 +35,14 @@ async function handleSubmit(payload: {
 			throw new Error('save failed');
 		}
 		goto(`/geschichten/${data.geschichte.id}`);
+	} catch (e) {
+		if (!errorMessage) {
+			console.error('Geschichte save failed', e);
+			errorMessage = getErrorMessage(undefined);
+		}
+		// Contract: onSubmit rejects on failure — both editors catch and keep
+		// their dirty state instead of disarming the unsaved-changes guard.
+		throw e;
 	} finally {
 		submitting = false;
 	}

frontend/src/routes/geschichten/new/StoryCreate.svelte

@@ -31,10 +31,18 @@ async function handleSubmit(payload: {
 		if (!res.ok) {
 			const code = (await res.json().catch(() => ({})))?.code;
 			errorMessage = getErrorMessage(code);
-			return;
+			throw new Error('create failed');
 		}
 		const created = await res.json();
 		goto(`/geschichten/${created.id}`);
+	} catch (e) {
+		if (!errorMessage) {
+			console.error('Story create failed', e);
+			errorMessage = getErrorMessage(undefined);
+		}
+		// Contract: onSubmit rejects on failure — GeschichteEditor catches and
+		// keeps its dirty state instead of disarming the unsaved-changes guard.
+		throw e;
 	} finally {
 		submitting = false;
 	}