test(autosave): observe saving→saved transition in B12 retry path

Tester #5506 §5: the existing test only asserted the final 'saved'
state, which would also pass if the hook skipped the saving state
altogether. Hold the second mocked saveFn promise so we can assert the
intermediate transition.

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

frontend/src/lib/hooks/__tests__/useBlockAutoSave.svelte.test.ts

@@ -72,8 +72,11 @@ describe('createBlockAutoSave', () => {
 	});
 
 	it('preserves the in-flight text + mentionedPersons across a save failure (B12)', async () => {
+		// Hold the second saveFn so we can observe the saving→saved transition
+		// (Tester #5506 §5).
+		let resolveSecond!: () => void;
 		mockSaveFn.mockRejectedValueOnce(new Error('boom'));
-		mockSaveFn.mockResolvedValueOnce(undefined);
+		mockSaveFn.mockReturnValueOnce(new Promise<void>((r) => (resolveSecond = r)));
 		const as = createBlockAutoSave({ saveFn: mockSaveFn, documentId: 'doc-1' });
 
 		const mentions: PersonMention[] = [{ personId: 'p-aug', displayName: 'Auguste Raddatz' }];
@@ -82,8 +85,14 @@ describe('createBlockAutoSave', () => {
 		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', []);
+		const retryPromise = as.handleRetry('block-1', 'should-not-be-used', []);
+		// Yield once so executeSave runs synchronously up to the saveFn await.
+		await Promise.resolve();
+		expect(as.getSaveState('block-1')).toBe('saving');
 		expect(mockSaveFn).toHaveBeenLastCalledWith('block-1', '@Auguste Raddatz hi', mentions);
+
+		resolveSecond();
+		await retryPromise;
 		expect(as.getSaveState('block-1')).toBe('saved');
 	});