fix: preserve hidden note title across editor modes

tests/title-visibility.test.mjs

@@ -0,0 +1,104 @@
+import assert from 'node:assert/strict';
+import { readFile } from 'node:fs/promises';
+import test from 'node:test';
+
+const { restoreTitleHeading, stripTitleHeading } = await import(
+  new URL('../src/lib/editor/titleVisibility.ts', import.meta.url)
+);
+const editorSource = await readFile(
+  new URL('../src/lib/components/Editor.svelte', import.meta.url),
+  'utf8'
+);
+
+test('rich to source transition strips the restored title before display', () => {
+  const start = editorSource.indexOf('if (isSource && !lastSourceMode) {');
+  const end = editorSource.indexOf('} else if (!isSource && lastSourceMode)', start);
+
+  assert.notEqual(start, -1, 'rich to source transition was not found');
+  assert.notEqual(end, -1, 'rich to source transition boundary was not found');
+  assert.match(
+    editorSource.slice(start, end),
+    /sourceContent\s*=\s*stripTitleH1\(\s*editor\s*\?\s*editorToMarkdown\(\)\s*:\s*\(\$activeNote\?\.content\s*\?\?\s*''\)\s*\)\s*;/
+  );
+});
+
+test('source to rich transition preserves the hidden title on desktop and mobile', () => {
+  const start = editorSource.indexOf('} else if (!isSource && lastSourceMode) {');
+  const end = editorSource.indexOf('// Tauri drag-drop listener', start);
+  const transition = editorSource.slice(start, end);
+
+  assert.notEqual(start, -1, 'source to rich transition was not found');
+  assert.notEqual(end, -1, 'source to rich transition boundary was not found');
+  assert.match(
+    transition,
+    /editor\.commands\.setContent\(\s*markdownToHtml\(\s*restoreTitleH1\(\s*content\s*\)\s*\)\s*\)\s*;/
+  );
+  assert.match(transition, /createEditor\(\s*restoreTitleH1\(\s*content\s*\)\s*\)\s*;/);
+});
+
+test('source to rich transition preserves an empty source body on desktop and mobile', () => {
+  const start = editorSource.indexOf('} else if (!isSource && lastSourceMode) {');
+  const end = editorSource.indexOf('// Tauri drag-drop listener', start);
+  const transition = editorSource.slice(start, end);
+  const contentAssignments = [...transition.matchAll(/const content = ([^;]+);/g)]
+    .map((match) => match[1].trim());
+
+  assert.deepEqual(contentAssignments, ['srcText', 'srcText']);
+  assert.doesNotMatch(transition, /srcText\s*\|\|/);
+});
+
+test('keeps a hidden title through source to rich to source and save', () => {
+  const persisted = '# Note title\n\n## Something else\n\nBody\n';
+  const body = '## Something else\n\nBody\n';
+
+  const initialSource = stripTitleHeading(persisted, 'Note title', true);
+  const rich = stripTitleHeading(
+    restoreTitleHeading(initialSource.markdown, initialSource.hiddenTitle),
+    'Note title',
+    true
+  );
+  const toggledSource = stripTitleHeading(
+    restoreTitleHeading(rich.markdown, rich.hiddenTitle),
+    'Note title',
+    true
+  );
+
+  assert.equal(rich.markdown, body);
+  assert.equal(toggledSource.markdown, body);
+  assert.equal(restoreTitleHeading(toggledSource.markdown, toggledSource.hiddenTitle), persisted);
+});
+
+test('keeps a title-only note visually empty and saves one title heading', () => {
+  const initialSource = stripTitleHeading('# Note title\n', 'Note title', true);
+  const rich = stripTitleHeading(
+    restoreTitleHeading(initialSource.markdown, initialSource.hiddenTitle),
+    'Note title',
+    true
+  );
+  const saved = restoreTitleHeading(rich.markdown, rich.hiddenTitle);
+
+  assert.equal(initialSource.markdown, '');
+  assert.equal(rich.markdown, '');
+  assert.equal((saved.match(/^# Note title$/gm) ?? []).length, 1);
+});
+
+test('replaces hidden title state when an unrelated note loads', () => {
+  const markdown = '## Something else\n\nOther body\n';
+  const start = editorSource.indexOf('function stripTitleH1(md: string): string {');
+  const end = editorSource.indexOf('function restoreTitleH1(md: string): string {', start);
+
+  assert.deepEqual(stripTitleHeading(markdown, 'Another note', true), {
+    markdown,
+    hiddenTitle: null
+  });
+  assert.match(editorSource.slice(start, end), /hiddenTitleHeading\s*=\s*result\.hiddenTitle\s*;/);
+});
+
+test('leaves the title visible when title hiding is disabled', () => {
+  const persisted = '# Note title\n\n## Something else\n';
+
+  assert.deepEqual(stripTitleHeading(persisted, 'Note title', false), {
+    markdown: persisted,
+    hiddenTitle: null
+  });
+});