Edit YAML frontmatter from the preview

package.json

@@ -8,6 +8,7 @@
 		"dev:installer": "tauri dev -- -- --install",
 		"build": "vite build",
 		"preview": "vite preview",
+		"test:frontmatter": "node --test --import tsx scripts/frontMatter.test.ts scripts/frontMatterDisclosure.test.ts",
 		"test:frontmatter": "node --test --import tsx scripts/frontMatter.test.ts",
 		"test:workflows": "node --test --import tsx scripts/exportHtml.test.ts scripts/exportOpenPrompt.test.ts scripts/reloadOpenToolbar.test.ts scripts/editorToolbar.test.ts scripts/titlebarToolbar.test.ts scripts/toolbarCustomizationWiring.test.ts",
 		"check": "svelte-kit sync && svelte-check --tsconfig ./tsconfig.json",

scripts/frontMatterDisclosure.test.ts

@@ -0,0 +1,34 @@
+import assert from 'node:assert/strict';
+import { readFileSync } from 'node:fs';
+import { test } from 'node:test';
+
+const viewerSource = readFileSync(new URL('../src/lib/MarkdownViewer.svelte', import.meta.url), 'utf8');
+
+test('front matter panel uses native details disclosure so collapsed summary remains expandable', () => {
+	const panelStart = viewerSource.indexOf('frontmatter-panel');
+	assert.notEqual(panelStart, -1);
+
+	const panelSource = viewerSource.slice(panelStart - 160, panelStart + 900);
+
+	assert.match(panelSource, /<details\b[^>]*class="frontmatter-panel"/);
+	assert.match(panelSource, /<summary\b[^>]*class="frontmatter-summary"/);
+	assert.doesNotMatch(panelSource, /<button\b[^>]*class="frontmatter-summary"/);
+});
+
+test('front matter panel is collapsed by default until the user opens it', () => {
+	assert.match(viewerSource, /frontMatterCollapsedByKey\[frontMatterPanelKey\]\s*\?\?\s*true/);
+	assert.match(viewerSource, /open=\{!isFrontMatterCollapsed\}/);
+});
+
+test('front matter list fields render as editable tags instead of one comma input', () => {
+	const listBranchStart = viewerSource.indexOf("field.kind === 'list'");
+	assert.notEqual(listBranchStart, -1);
+
+	const listBranch = viewerSource.slice(listBranchStart, listBranchStart + 4000);
+
+	assert.match(listBranch, /class="frontmatter-tags"/);
+	assert.match(listBranch, /class="frontmatter-tag-remove"/);
+	assert.match(listBranch, /class="frontmatter-tag-add-button"/);
+	assert.match(listBranch, /startFrontMatterTagEdit/);
+	assert.match(listBranch, /value=\{getFrontMatterTagDraft\(field\)\}/);
+});