fix(tray-icons): standardize missing icon fallback

src/desktop/trayIcons/backgroundAppsSource.ts

@@ -5,7 +5,7 @@ import Gio from '@girs/gio-2.0';
 import GLib from '@girs/glib-2.0';
 import Shell from '@girs/shell-18';
 
-import type { TrayItem, TrayItemStatus } from './trayState.ts';
+import { TRAY_ICON_FALLBACK_NAME, type TrayItem, type TrayItemStatus } from './trayState.ts';
 import { logger } from '~/core/logger.ts';
 
 const DBUS_NAME = 'org.freedesktop.background.Monitor';
@@ -126,7 +126,7 @@ export class BackgroundAppsSource {
     return {
       id: `bg:${appId}`,
       get icon() {
-        return app.get_icon() || 'application-x-executable-symbolic';
+        return app.get_icon() || TRAY_ICON_FALLBACK_NAME;
       },
       get tooltip() {
         return message || '';

src/desktop/trayIcons/sniHost.ts

@@ -5,7 +5,7 @@ import GLib from '@girs/glib-2.0';
 import GdkPixbuf from '@girs/gdkpixbuf-2.0';
 import St from '@girs/st-18';
 
-import type { TrayItem, TrayItemStatus } from './trayState.ts';
+import { TRAY_ICON_FALLBACK_NAME, type TrayItem, type TrayItemStatus } from './trayState.ts';
 import type { SniWatcher } from './sniWatcher.ts';
 import { sniIdentityMatchesAppId } from './appIdentity.ts';
 import { isSymbolicSniArgb } from './sniIconState.ts';
@@ -231,7 +231,7 @@ export class SniHost {
     }
 
     logger.debug(`SNI icon ${itemId} reason=${reason} source=fallback`, { prefix: LOG_PREFIX });
-    return 'image-missing-symbolic';
+    return TRAY_ICON_FALLBACK_NAME;
   }
 
   refreshIcons(reason = 'theme-change'): void {

src/desktop/trayIcons/trayIconItem.ts

@@ -9,7 +9,7 @@ import * as PopupMenu from '@girs/gnome-shell/ui/popupMenu';
 import { PopupAnimation } from '@girs/gnome-shell/ui/boxpointer';
 import { logger } from '~/core/logger.ts';
 
-import type { TrayItem } from './trayState.ts';
+import { TRAY_ICON_FALLBACK_NAME, type TrayItem } from './trayState.ts';
 import { DBusMenuClient } from './dbusMenu.ts';
 
 const BADGE_SIZE = 6;
@@ -108,7 +108,7 @@ export const TrayIconItem = GObject.registerClass(
 
       this._iconWidget = new St.Icon({
         icon_size: iconSize,
-        fallback_icon_name: 'image-missing-symbolic',
+        fallback_icon_name: TRAY_ICON_FALLBACK_NAME,
         reactive: false,
       });
       box.add_child(this._iconWidget);

src/desktop/trayIcons/trayState.ts

@@ -1,6 +1,8 @@
 import type Gio from '@girs/gio-2.0';
 import type GdkPixbuf from '@girs/gdkpixbuf-2.0';
 
+export const TRAY_ICON_FALLBACK_NAME = 'application-x-executable-symbolic';
+
 export type TrayItemStatus = 'Passive' | 'Active' | 'NeedsAttention';
 
 export type TrayMenuItem = { label: string; action: () => void };

tests/unit/desktop/trayIcons/trayState.test.ts

@@ -6,9 +6,14 @@ import {
   applyScroll,
   addAttention,
   clearAttention,
+  TRAY_ICON_FALLBACK_NAME,
 } from '~/desktop/trayIcons/trayState.ts';
 import type { TrayItem } from '~/desktop/trayIcons/trayState.ts';
 
+test('Tray Icons use the generic executable icon as their shared fallback', () => {
+  assert.strictEqual(TRAY_ICON_FALLBACK_NAME, 'application-x-executable-symbolic');
+});
+
 test('createTrayState returns collapsed=true, offset=0, empty attention set', () => {
   const state = createTrayState();
   assert.strictEqual(state.collapsed, true);