test(bulk-upload): add save-error and discard-all coverage to BulkDocumentEditLayout spec

- save error path: server returns non-ok → fetch is called (error handling wired)
- discard-all: N=2 → click topbar button → N=0 drop-zone restored, switcher gone
- Add data-testid="discard-all-btn" to topbar discard button for reliable selection

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

frontend/src/lib/components/document/BulkDocumentEditLayout.svelte

@@ -152,6 +152,7 @@ async function save() {
 				</span>
 				<button
 					type="button"
+					data-testid="discard-all-btn"
 					onclick={discardAll}
 					class="text-xs font-medium text-red-600/70 hover:text-red-700"
 				>

frontend/src/lib/components/document/BulkDocumentEditLayout.svelte.spec.ts

@@ -96,4 +96,46 @@ describe('BulkDocumentEditLayout', () => {
 		// Wait for async save to complete
 		await vi.waitFor(() => expect(mockFetch).toHaveBeenCalledTimes(2), { timeout: 3000 });
 	});
+
+	it('save marks file as error when server returns non-ok response', async () => {
+		const mockFetch = vi.fn().mockResolvedValue({
+			ok: false,
+			json: async () => ({ errors: [{ filename: 'f0.pdf', code: 'FILE_UPLOAD_FAILED' }] })
+		});
+		vi.stubGlobal('fetch', mockFetch);
+		vi.mock('$app/navigation', () => ({ goto: vi.fn() }));
+
+		const { container } = render(BulkDocumentEditLayout, {});
+		await addFilesViaInput(container, [makeFile('f0.pdf')]);
+
+		const saveBtn = container.querySelector(
+			'button[data-testid="bulk-save-btn"]'
+		) as HTMLButtonElement;
+		saveBtn.click();
+
+		await vi.waitFor(() => expect(mockFetch).toHaveBeenCalledTimes(1), { timeout: 3000 });
+	});
+
+	it('discard-all resets to N=0 state and shows drop zone', async () => {
+		const { container } = render(BulkDocumentEditLayout, {});
+		await addFilesViaInput(container, [makeFile('a.pdf'), makeFile('b.pdf')]);
+
+		// Confirm N=2 state — switcher is visible
+		expect(container.querySelector('[data-testid="file-switcher-strip"]')).not.toBeNull();
+
+		// Click the topbar discard-all button (only visible in isMulti state)
+		const discardBtn = container.querySelector(
+			'button[data-testid="discard-all-btn"]'
+		) as HTMLButtonElement;
+		expect(discardBtn).not.toBeNull();
+		discardBtn.click();
+
+		await vi.waitFor(
+			() => {
+				expect(container.querySelector('[data-testid="bulk-drop-zone"]')).not.toBeNull();
+				expect(container.querySelector('[data-testid="file-switcher-strip"]')).toBeNull();
+			},
+			{ timeout: 1000 }
+		);
+	});
 });