feat(#248): add TagAncestry and TagChildrenPreview components

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

frontend/src/routes/admin/tags/[id]/TagAncestry.svelte

@@ -0,0 +1,43 @@
+<script lang="ts">
+import { m } from '$lib/paraglide/messages.js';
+
+type FlatTag = {
+	id: string;
+	name: string;
+	color?: string;
+	parentId?: string;
+	documentCount: number;
+};
+
+interface Props {
+	tag: { name: string; parentId?: string };
+	allTags: FlatTag[];
+}
+
+let { tag, allTags }: Props = $props();
+
+const ancestors = $derived.by(() => {
+	const chain: FlatTag[] = [];
+	let current: FlatTag | undefined = allTags.find((t) => t.id === tag.parentId);
+	while (current) {
+		chain.push(current);
+		const parentId = current.parentId;
+		current = parentId ? allTags.find((t) => t.id === parentId) : undefined;
+	}
+	return chain.reverse();
+});
+</script>
+
+{#if ancestors.length > 0}
+	<nav aria-label={m.admin_tag_ancestry_label()}>
+		<ol class="flex items-center gap-1 text-xs text-ink-3">
+			{#each ancestors as ancestor (ancestor.id)}
+				<li>
+					<a href="/admin/tags/{ancestor.id}" class="hover:text-ink">{ancestor.name}</a>
+				</li>
+				<li aria-hidden="true">›</li>
+			{/each}
+			<li class="text-ink">{tag.name}</li>
+		</ol>
+	</nav>
+{/if}

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

@@ -0,0 +1,60 @@
+import { afterEach, describe, expect, it } from 'vitest';
+import { cleanup, render } from 'vitest-browser-svelte';
+import { page } from 'vitest/browser';
+import TagAncestry from './TagAncestry.svelte';
+
+afterEach(cleanup);
+
+const allTags = [
+	{ id: 't1', name: 'Root', documentCount: 0 },
+	{ id: 't2', name: 'Child', parentId: 't1', documentCount: 0 },
+	{ id: 't3', name: 'Grandchild', parentId: 't2', documentCount: 0 }
+];
+
+describe('TagAncestry', () => {
+	it('renders nothing for a root tag', async () => {
+		const { container } = render(TagAncestry, {
+			tag: { id: 't1', name: 'Root', documentCount: 0 },
+			allTags
+		});
+		expect(container.querySelector('nav')).toBeFalsy();
+	});
+
+	it('renders a nav element for a child tag', async () => {
+		const { container } = render(TagAncestry, {
+			tag: { id: 't2', name: 'Child', parentId: 't1', documentCount: 0 },
+			allTags
+		});
+		expect(container.querySelector('nav')).toBeTruthy();
+	});
+
+	it('shows parent name as a link', async () => {
+		render(TagAncestry, {
+			tag: { id: 't2', name: 'Child', parentId: 't1', documentCount: 0 },
+			allTags
+		});
+		await expect.element(page.getByRole('link', { name: 'Root' })).toBeInTheDocument();
+		await expect
+			.element(page.getByRole('link', { name: 'Root' }))
+			.toHaveAttribute('href', '/admin/tags/t1');
+	});
+
+	it('shows full ancestor chain for deeply nested tag', async () => {
+		render(TagAncestry, {
+			tag: { id: 't3', name: 'Grandchild', parentId: 't2', documentCount: 0 },
+			allTags
+		});
+		await expect.element(page.getByRole('link', { name: 'Root' })).toBeInTheDocument();
+		await expect.element(page.getByRole('link', { name: 'Child' })).toBeInTheDocument();
+	});
+
+	it('does not render current tag as a link', async () => {
+		render(TagAncestry, {
+			tag: { id: 't2', name: 'Child', parentId: 't1', documentCount: 0 },
+			allTags
+		});
+		const links = document.querySelectorAll('nav a');
+		const linkTexts = Array.from(links).map((a) => a.textContent?.trim());
+		expect(linkTexts).not.toContain('Child');
+	});
+});

frontend/src/routes/admin/tags/[id]/TagChildrenPreview.svelte

@@ -0,0 +1,52 @@
+<script lang="ts">
+import { m } from '$lib/paraglide/messages.js';
+
+type FlatTag = {
+	id: string;
+	name: string;
+	color?: string;
+	parentId?: string;
+	documentCount: number;
+};
+
+interface Props {
+	tag: { id: string };
+	allTags: FlatTag[];
+}
+
+let { tag, allTags }: Props = $props();
+
+let showAll = $state(false);
+
+const children = $derived(allTags.filter((t) => t.parentId === tag.id));
+const visibleChildren = $derived(showAll ? children : children.slice(0, 5));
+</script>
+
+{#if children.length > 0}
+	<div
+		data-testid="children-preview"
+		class="mb-5 rounded-sm border border-line bg-surface p-5 shadow-sm"
+	>
+		<h3 class="mb-3 text-xs font-bold tracking-widest text-ink-3 uppercase">
+			{m.admin_tag_children_label()}
+		</h3>
+		<div class="flex flex-wrap gap-2">
+			{#each visibleChildren as child (child.id)}
+				<a
+					href="/admin/tags/{child.id}"
+					class="rounded-full border border-line bg-surface px-3 py-1 text-xs text-ink hover:bg-accent-bg"
+					>{child.name}</a
+				>
+			{/each}
+			{#if !showAll && children.length > 5}
+				<button
+					type="button"
+					data-testid="expand-children"
+					onclick={() => showAll = true}
+					class="rounded-full border border-line bg-surface px-3 py-1 text-xs text-ink-3 hover:text-ink"
+					>{m.admin_tag_children_more({ count: children.length - 5 })}</button
+				>
+			{/if}
+		</div>
+	</div>
+{/if}

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

@@ -0,0 +1,75 @@
+import { afterEach, describe, expect, it } from 'vitest';
+import { cleanup, render } from 'vitest-browser-svelte';
+import { page } from 'vitest/browser';
+import TagChildrenPreview from './TagChildrenPreview.svelte';
+
+afterEach(cleanup);
+
+const allTags = [
+	{ id: 't1', name: 'Root', documentCount: 0 },
+	{ id: 't2', name: 'Alpha', parentId: 't1', documentCount: 0 },
+	{ id: 't3', name: 'Beta', parentId: 't1', documentCount: 0 },
+	{ id: 't4', name: 'Gamma', parentId: 't1', documentCount: 0 },
+	{ id: 't5', name: 'Delta', parentId: 't1', documentCount: 0 },
+	{ id: 't6', name: 'Epsilon', parentId: 't1', documentCount: 0 },
+	{ id: 't7', name: 'Zeta', parentId: 't1', documentCount: 0 }
+];
+
+describe('TagChildrenPreview', () => {
+	it('renders nothing for a leaf tag', async () => {
+		const { container } = render(TagChildrenPreview, {
+			tag: { id: 't2', name: 'Alpha', parentId: 't1', documentCount: 0 },
+			allTags
+		});
+		expect(container.querySelector('[data-testid="children-preview"]')).toBeFalsy();
+	});
+
+	it('renders section heading for a tag with children', async () => {
+		render(TagChildrenPreview, {
+			tag: { id: 't1', name: 'Root', documentCount: 0 },
+			allTags
+		});
+		await expect.element(page.getByTestId('children-preview')).toBeInTheDocument();
+	});
+
+	it('shows up to 5 children as chips', async () => {
+		render(TagChildrenPreview, {
+			tag: { id: 't1', name: 'Root', documentCount: 0 },
+			allTags
+		});
+		// Alpha through Epsilon should be visible (5 chips)
+		await expect.element(page.getByText('Alpha')).toBeInTheDocument();
+		await expect.element(page.getByText('Epsilon')).toBeInTheDocument();
+	});
+
+	it('shows expand button when there are more than 5 children', async () => {
+		render(TagChildrenPreview, {
+			tag: { id: 't1', name: 'Root', documentCount: 0 },
+			allTags
+		});
+		// There are 6 children — should show "und 1 weitere" expand button
+		const expandBtn = document.querySelector<HTMLButtonElement>(
+			'button[data-testid="expand-children"]'
+		);
+		expect(expandBtn).toBeTruthy();
+	});
+
+	it('expand button reveals hidden children inline', async () => {
+		render(TagChildrenPreview, {
+			tag: { id: 't1', name: 'Root', documentCount: 0 },
+			allTags
+		});
+		// Zeta is hidden behind the expand button
+		await expect.element(page.getByText('Zeta')).not.toBeInTheDocument();
+		await page.getByTestId('expand-children').click();
+		await expect.element(page.getByText('Zeta')).toBeInTheDocument();
+	});
+
+	it('does not show expand button when children count <= 5', async () => {
+		render(TagChildrenPreview, {
+			tag: { id: 't1', name: 'Root', documentCount: 0 },
+			allTags: allTags.slice(0, 4) // Root + 3 children
+		});
+		expect(document.querySelector('[data-testid="expand-children"]')).toBeFalsy();
+	});
+});