feat(terminal): add persistent browser font size controls

test/terminal-preferences.test.js

@@ -0,0 +1,29 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { FONT_SIZE_KEY, readFontSize, saveFontSize } from '../public/terminal-preferences.js';
+
+test('terminal font size persists and falls back to 10 for missing or corrupt preferences', () => {
+  const values = new Map();
+  const storage = {
+    getItem: (key) => values.get(key) ?? null,
+    setItem: (key, value) => values.set(key, value)
+  };
+  assert.equal(readFontSize(storage), 10);
+  assert.equal(saveFontSize(18, storage), true);
+  assert.equal(readFontSize(storage), 18);
+  for (const value of ['garbage', '7', '33', '12.5', 'Infinity']) {
+    values.set(FONT_SIZE_KEY, value);
+    assert.equal(readFontSize(storage), 10);
+  }
+  assert.equal(saveFontSize(32, storage), true);
+  assert.equal(readFontSize(storage), 32);
+});
+
+test('blocked browser storage preserves the default and reports that saving failed', () => {
+  const storage = {
+    getItem: () => { throw new Error('Storage blocked'); },
+    setItem: () => { throw new Error('Storage blocked'); }
+  };
+  assert.equal(readFontSize(storage), 10);
+  assert.equal(saveFontSize(16, storage), false);
+});