Add per-notebook icons and sync

tests/notebook-icons.test.mjs

@@ -0,0 +1,27 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+
+const source = await import(new URL('../src/lib/utils/notebook-icons.ts', import.meta.url));
+
+const {
+  NOTEBOOK_ICON_OPTIONS,
+  decodeBuiltinNotebookIcon,
+  encodeBuiltinNotebookIcon
+} = source;
+
+test('built-in notebook icons have stable unique storage values', () => {
+  assert.equal(NOTEBOOK_ICON_OPTIONS.length, 16);
+  assert.equal(new Set(NOTEBOOK_ICON_OPTIONS.map(({ id }) => id)).size, NOTEBOOK_ICON_OPTIONS.length);
+
+  for (const { id } of NOTEBOOK_ICON_OPTIONS) {
+    const stored = encodeBuiltinNotebookIcon(id);
+    assert.equal(stored, `builtin:${id}`);
+    assert.equal(decodeBuiltinNotebookIcon(stored), id);
+  }
+});
+
+test('custom paths and unknown built-in values remain outside the icon codec', () => {
+  assert.equal(decodeBuiltinNotebookIcon('.helixnotes/attachments/notebook-icon.png'), null);
+  assert.equal(decodeBuiltinNotebookIcon('builtin:unknown'), null);
+  assert.equal(decodeBuiltinNotebookIcon(null), null);
+});