feat: add federation state globals and test-only helpers to app.js

Add new module-level globals:
- let _gridViewMode = 'flat'
- let _activeFilterDevice = 'all'

Add test-only helper functions:
- _setSources(sources): sets internal _sources array
- _setServerSettings(settings): sets internal _serverSettings
- _getGridViewMode(): returns current _gridViewMode value
- _getSources(): returns current _sources array

All 4 helpers exported in module.exports.

Tests added (all passing, 143/143):
- '_setSources sets internal _sources array'
- '_setServerSettings sets internal _serverSettings'
- '_getGridViewMode returns current _gridViewMode value'
- '_getSources returns current _sources array'

Task: task-3 (federation state helpers)

muxplex/frontend/app.js

@@ -134,6 +134,8 @@ var _previewSessionName = null;  // track by NAME, not DOM element
 let _sources = [];
 let _settingsOpen = false;
 let _serverSettings = null;
+let _gridViewMode = 'flat';
+let _activeFilterDevice = 'all';
 const DISPLAY_SETTINGS_KEY = 'muxplex.display';
 const DISPLAY_DEFAULTS = {
   fontSize: 14,
@@ -1671,6 +1673,18 @@ function _setViewMode(mode) {
   _viewMode = mode;
 }
 
+/** Test-only: set _sources directly. */
+function _setSources(sources) { _sources = sources; }
+
+/** Test-only: set _serverSettings directly. */
+function _setServerSettings(settings) { _serverSettings = settings; }
+
+/** Test-only: get _gridViewMode. */
+function _getGridViewMode() { return _gridViewMode; }
+
+/** Test-only: get _sources. */
+function _getSources() { return _sources; }
+
 document.addEventListener('DOMContentLoaded', () => {
   initDeviceId();
   applyDisplaySettings(loadDisplaySettings());
@@ -1759,5 +1773,9 @@ if (typeof module !== 'undefined' && module.exports) {
     // Test-only helpers
     _setCurrentSessions,
     _setViewMode,
+    _setSources,
+    _setServerSettings,
+    _getGridViewMode,
+    _getSources,
   };
 }

muxplex/frontend/tests/test_app.mjs

@@ -2004,6 +2004,28 @@ test('createNewSession polls for session before auto-opening (not immediate setT
   );
 });
 
+// --- federation state helpers (task-3) ---
+
+test('_setSources sets internal _sources array', () => {
+  assert.doesNotThrow(() => app._setSources([{ url: '', name: 'test' }]));
+});
+
+test('_setServerSettings sets internal _serverSettings', () => {
+  assert.doesNotThrow(() => app._setServerSettings({ sort_order: 'recent' }));
+});
+
+test('_getGridViewMode returns current _gridViewMode value', () => {
+  assert.strictEqual(typeof app._getGridViewMode(), 'string', '_getGridViewMode should return a string');
+  assert.strictEqual(app._getGridViewMode(), 'flat', '_gridViewMode should default to flat');
+});
+
+test('_getSources returns current _sources array', () => {
+  app._setSources([{ url: 'http://test', name: 'Test' }]);
+  const sources = app._getSources();
+  assert.ok(Array.isArray(sources), '_getSources should return an array');
+  assert.strictEqual(sources[0].url, 'http://test', '_getSources should return value set by _setSources');
+});
+
 // --- buildSources ---
 
 test('buildSources returns only local source when no remote_instances', () => {