diff --git a/frontend/src/lib/hooks/__tests__/useBlockAutoSave.svelte.test.ts b/frontend/src/lib/hooks/__tests__/useBlockAutoSave.svelte.test.ts
index 8e2633e0..93806949 100644
--- a/frontend/src/lib/hooks/__tests__/useBlockAutoSave.svelte.test.ts
+++ b/frontend/src/lib/hooks/__tests__/useBlockAutoSave.svelte.test.ts
@@ -71,6 +71,22 @@ describe('createBlockAutoSave', () => {
 		expect(as.getSaveState('block-1')).toBe('saved');
 	});
 
+	it('preserves the in-flight text + mentionedPersons across a save failure (B12)', async () => {
+		mockSaveFn.mockRejectedValueOnce(new Error('boom'));
+		mockSaveFn.mockResolvedValueOnce(undefined);
+		const as = createBlockAutoSave({ saveFn: mockSaveFn, documentId: 'doc-1' });
+
+		const mentions: PersonMention[] = [{ personId: 'p-aug', displayName: 'Auguste Raddatz' }];
+		as.handleTextChange('block-1', '@Auguste Raddatz hi', mentions);
+		await vi.advanceTimersByTimeAsync(1500);
+		expect(as.getSaveState('block-1')).toBe('error');
+
+		// Retry without re-passing the data — the hook resends the preserved payload.
+		await as.handleRetry('block-1', 'should-not-be-used', []);
+		expect(mockSaveFn).toHaveBeenLastCalledWith('block-1', '@Auguste Raddatz hi', mentions);
+		expect(as.getSaveState('block-1')).toBe('saved');
+	});
+
 	it('clearBlock removes all state for a block', () => {
 		const as = createBlockAutoSave({ saveFn: mockSaveFn, documentId: 'doc-1' });
 		as.handleTextChange('block-1', 'text', NO_MENTIONS);