test(admin-tags): pin merge/delete previews to the direct count (#698)

Characterization tests for AC#8: the merge preview and the delete-impact
warning describe direct-document operations, so they must report the tag's
direct documentCount, never a subtree rollup. Both tests pass a stray
subtreeDocumentCount and assert it does not leak into the preview, so a future
change can't silently desync a destructive-action preview.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/routes/admin/tags/[id]/TagDeleteGuard.svelte.spec.ts

@@ -68,6 +68,21 @@ describe('TagDeleteGuard', () => {
 		renderWithConfirm();
 		await expect.element(page.getByText(/3 Dokument/)).toBeInTheDocument();
 	});
+
+	// Characterization (#698): the delete-impact warning describes a destructive single-tag delete,
+	// which removes only the tag's DIRECT document_tags rows — so it must show documentCount, never
+	// a subtree rollup. Pinned so a future change can't silently desync this warning.
+	it('shows the direct documentCount in the impact summary, not a subtree rollup', async () => {
+		const tagWithStraySubtree = {
+			id: 't1',
+			name: 'Familie',
+			documentCount: 3,
+			subtreeDocumentCount: 99
+		};
+		renderWithConfirm({ tag: tagWithStraySubtree, allTags });
+		await expect.element(page.getByText(/3 Dokument/)).toBeInTheDocument();
+		expect(document.body.textContent).not.toContain('99');
+	});
 });
 
 describe('TagDeleteGuard – confirmation dialog', () => {

frontend/src/routes/admin/tags/[id]/TagMergeZone.svelte.spec.ts

@@ -66,6 +66,32 @@ describe('TagMergeZone – step flow', () => {
 	});
 });
 
+describe('TagMergeZone – preview uses the direct document count (characterization, #698)', () => {
+	it('shows the tag direct documentCount in the merge preview, not a subtree rollup', async () => {
+		vi.stubGlobal(
+			'fetch',
+			vi.fn().mockResolvedValue({
+				ok: true,
+				json: vi.fn().mockResolvedValue([{ id: 't2', name: 'Reise' }])
+			})
+		);
+		// documentCount (direct) = 3; a stray subtree rollup of 99 must NOT leak into the preview —
+		// merge re-tags only direct documents, so the preview has to stay the direct count.
+		const mergeTag = { id: 't1', name: 'Familie', documentCount: 3, subtreeDocumentCount: 99 };
+		render(TagMergeZone, { tag: mergeTag, allTags, form: null });
+
+		const input = page.getByRole('combobox');
+		await input.fill('R');
+		await vi.advanceTimersByTimeAsync(300);
+		await page.getByRole('option', { name: 'Reise' }).click();
+		await vi.advanceTimersByTimeAsync(0);
+
+		await expect.element(page.getByTestId('merge-step2')).toBeInTheDocument();
+		expect(document.body.textContent).toContain('3 Dokumente');
+		expect(document.body.textContent).not.toContain('99');
+	});
+});
+
 describe('TagMergeZone – stale state reset', () => {
 	it('resets target selection when tag prop changes', async () => {
 		vi.stubGlobal(